Patent Publication Number: US-2021189349-A1

Title: Esophageal tissue and/or organoid compositions and methods of making same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and benefit of U.S. Provisional Application 62/570,182, to James Wells, filed Oct. 10, 2017, the contents of which incorporated in its entirety for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH 
     This invention was made with U.S. government support NIH grant number P01HD093363. The U.S. government has certain rights in this invention. 
    
    
     BACKGROUND 
     The esophagus actively facilitates the passing of food from the oral cavity and pharynx to the stomach. It consists of a stratified squamous epithelium, muscle layers, and an enteric nervous system to sense stretch and control peristalsis. Congenital diseases such as esophageal atresia are caused by gene mutations that result in luminal narrowing or discontinuity. Other diseases affect the esophagus later in life, such as esophageal carcinoma, eosinophilic esophagitis, achalasia and other motility disorders. Tracheal and esophageal disorders are prevalent in humans and are difficult to accurately model in mice. Despite the prevalence of the aforementioned disease states, and because there are substantial differences in tissue architecture between mouse and human esophagus, there is a need in the art for human esophageal tissue models for research. The instant disclosure addresses one or more of the aforementioned needs in the art. 
     BRIEF SUMMARY 
     The instant disclosure relates to methods for converting mammalian definitive endoderm (DE) cells into specific tissue(s) or organ(s) through directed differentiation. In particular, the disclosure relates to formation of esophageal tissue and/or organoids formed from differentiated definitive endoderm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Those of skill in the art will understand that the drawings, described below, are for illustrative purposes only. The drawings are not intended to limit the scope of the present teachings in any way. 
         FIGS. 1A-1K . Specifying anterior foregut fate by modulating Wnt and retinoic acid signaling during foregut spheroid development. ( 1 A) The experimental protocol to pattern foregut spheroids along anterior-posterior axis by manipulating the duration of Wnt activation (chiron-chr). ( 1 B- 1 C) qPCR analysis of varying chiron treatment duration on patterning of foregut spheroids as measured by ( 1 B) the foregut marker SOX2 and mid/hindgut marker CDX2, and ( 1 C) the anterior foregut (“AFG”) marker HNF1B, and the posterior foregut markers PROX1 and HNF6. (D-E) Whole-mount immunofluorescence (“IF”) analysis with HNF1B, SOX2 and CTNNB1 of nascent spheroids (day 6) treated with 1 day ( 1 D) and 3 days ( 1 E) of chiron. ( 1 F) The experimental protocol to pattern foregut spheroids along anterior-posterior axis using retinoic acid (RA). ( 1 G) Effects of varying the duration of RA treatment on 3-day-old foregut spheroids as measured by SOX2, TP63 (AN isoform), GATA4, and PDX1. ( 1 J- 1 K) IF analysis on early esophageal markers SOX2 and p63 in untreated spheroids (H), and spheroids treated with RA for 1 day ( 1 J) or 4 days ( 1 K).  1   l - 1 ,  1 J- 1 , and  1 K- 1  show p63 staining alone ( 1 H) Quantification of the percent of SOX2+ and p63+ epithelial cells per spheroid. Scale bar=25 μm. See quantification and statistical analysis section for details. See also  FIG. 8  and  FIG. 9A-R . 
         FIGS. 2A-2I . Anterior foregut spheroids have esophageal-respiratory competence. ( 2 A) Schematic depicting experimental protocol to pattern AFG spheroids along the dorsal-ventral axis. ( 2 B) Current simplified model of the cues guiding dorsal-ventral patterning of the AFG of mouse and frog embryos. ( 2 C- 2 G) qPCR analysis of 3-day-old spheroids (day 9) treated for 3 days with Noggin, untreated (−ctrl), or chiron and BMP4 (10 ng/mL) using dorsal markers SOX2 and MNX1 ( 2 C+ 2 E), the respiratory marker NKX2-1 ( 2 D), ΔN splice variant of TP63 ( 2 F), and the stratified squamous epithelium marker KRT4 ( 2 G). ( 2 H- 2 I) IF staining for SOX2, NKX2-1, CDH1, and nuclei (DAPI) in Noggin ( 2 H) versus chiron+BMP4 ( 2 I) treated spheroids. Scale bar=25 μm. See quantification and statistical analysis section for details. See also  FIG. 10A-10J . 
         FIGS. 3A-3Y . Dorsal anterior foregut spheroids form organoids comprised of a stratified squamous epithelium that expresses esophageal markers. ( 3 A) Schematic depicting differentiation of DE into human esophageal organoids (HEOs). ( 3 B- 3 F) Brightfield images depicting growth of nascent spheroids into HEOs. (G-R) Comparison of E17.5 esophagi (G,J,M,K) to 1- and 2-month-old HEOs ( 3 H- 3 I,  3 K- 3 L,  3 N- 3 O,  3 Q- 3 R), by IF analysis of the transcription factors Sox2 and p63 ( 3 G- 3 I), epithelial markers Krt8 versus Krt14 ( 3 J- 3 O), and the suprabasal marker Krt13 ( 3 P- 3 R). ( 3 S- 3 V) qPCR analysis of the identity and maturation of esophageal organoids at 1- and 2-months of age compared to human gastric and intestinal organoids (HGO and HIO) and pediatric esophageal biopsies by the stratified squamous epithelial markers p63, KRT5, KRT13, IVL, CRNN. ( 3 W) Unsupervised hierarchical clustering of 2-month HEOs compared to various biopsies of the GI tract. ( 3 X) Principal component analysis of 1-month old HIOs, HGOs, and HEOs. ( 3 Y) Heat map of log 2-transformed normalized TPM values of selected genes (esophageal, gastric, intestinal) averaged across replicates. SSE=stratified squamous epithelium; b=basal; sb=suprabasal. Scale bar=500 μm ( 3 B- 3 F), 50 μm ( 3 G- 3 L), 100 μm ( 3 O- 3 R), and 25 μm ( 3 O- 1 - 3 R- 1 ). See quantification and statistical analysis section for details. See also  FIG. 11A-11CC . 
         FIGS. 4A-4BB . HEOs contain progenitors that give rise to differentiated stratified squamous epithelium. ( 4 A- 4 B) H&amp;E staining comparing 7-week HEOs to organotypic rafts generated using HEO-derived from keratinocytes. ( 4 C- 4 N) Comparison of 7-week HEOs to organotypic rafts by IF analysis of transcription factors SOX2 and p63 ( 4 C- 4 D), basal marker KRT14 ( 4 E- 4 F), suprabasal keratins KRT4 ( 4 G- 4 H) and KRT13 ( 4 I- 4 J), and differentiated markers IVL, CRNN, and FLG ( 4 K- 4 N). ( 4 O- 4 U) qPCR analysis of esophageal biopsies, 7-week HEOs, HEO-derived keratinocytes, and organotypic rafts for SOX2 and TP63 ( 4 O), KRT5 ( 4 P), KRT14 ( 4 Q), KRT4 and KRT13 ( 4 R), IVL ( 4 S), CRNN ( 4 T), and esophageal specific markers TMPRSS11A/D ( 4 U). ( 4 V) Protocol for EdU pulse-chase labeling experiment in HEOs. ( 4 W- 4 Z) IF images of HEOs at various time-points post-labeling. ( 4 AA- 4 BB) Analysis of IF images using a 2D histogram of P63 intensity versus EdU intensity. ( 4 AA) and a 1D histogram of percent of total EdU labeled cells versus distance from the epithelial base ( 4 BB). b=basal; sb=suprabasal. Scale bar=50 μm (C-N), 100 μm ( 4 A- 4 B,  4 S- 4 V). See quantification and statistical analysis section for details. See also  FIG. 12A-12R . 
         FIGS. 5A-5L . Early endodermal deletion of Sox2 results in esophageal agenesis in mouse. ( 5 A- 5 D) IF analysis for Sox2 and Nkx2-1 in control embryos (Sox2 fl/fl ) and Sox2 conditional endodermal knockout embryos (Sox2-DE-LOF, FoxA2 CreER ; Sox2 fl/fl ) from pregnant dams gavaged with tamoxifen at 6.5 dpc. Embryo sections at E9.5 ( 5 A- 5 B) and whole-mount IF at E11.5 ( 5 C- 5 D) in which the image is masked highlight the endoderm. ( 5 E- 5 F) IF images of sections with the relative section indicated in the whole-mount images ( 5 C- 5 D) for Nkx2-1 ( 5 E) and p63 ( 5 F). Insets show only the Sox2 channel (left) and the green/right (Nkx2-1 or p63) channel ( 5 G- 5 H) Analysis of cell death by cleaved Caspase 3 staining in E10.5 Sox2 cKO (Sox2 CreER/fl ) embryos from pregnant dams gavaged at 8.5 dpc. The boxed region is magnified and shown in ( 5 G- 1 - 5 H- 1 ), with the endoderm is outlined in white and displays only the cleaved Caspase 3. ( 5 I- 5 L) IF analysis of E11.5 mouse control and Sox2 cKO embryos (Sox2 CreER/fl ) from pregnant dams gavaged at 9.5 dpc. ( 5 I and  5 J) Whole-mount IF for Nkx2-1 and Foxa2 of the foregut from a side and frontal projection. ( 5 K and  5 L) Sections of the E11.5 foregut corresponding to their relative position in the whole-mount IF projections ( 5 I- 5 J), stained for Nkx2-1 ( 5 K) and p63 ( 5 J), with the yellow arrowhead pointing at the mutant esophagus. Scale bar=50 μm in all IF sections, and 100 μm in all IF whole-mount projections. See quantification and statistical analysis section for details. fg=foregut, dfg=dorsal foregut, vfg=ventral foregut, eso=esophagus, tr=trachea, br=bronchi, st=stomach. See also  FIG. 13A-13F . 
         FIGS. 6A-6T . Sox2 represses the respiratory fate and promotes the dorsal (esophageal) lineage. ( 6 A- 6 F) In situ hybridization for nkx2-1 of control ( 6 A,  6 C,  6 E) or Sox2 MO-injected ( 6 B,  6 D,  6 F)  Xenopus  endoderm explants analyzed at stage NF35 treated with Bio (GSK3(3 inhibitor) and Bio+BMP4. ( 6 G) Schematic depicting experimental protocol to generate human dorsal (Noggin) and ventral (BMP) AFG cultures. +SOX2 indicates tet-inducible SOX2, while −SOX2 indicates SOX2 CRISPRi. ( 6 H- 6 N) Analysis of day 9 AFG cultures patterned along the dorsal-ventral axis, with or without SOX2 knockdown in the dorsal cultures using Dox-inducible CRISPRi on day 3-9; ( 6 H- 6 K) IF staining of cultures for SOX2 and NKX2-1 and quantification in ( 6 L). ( 6 M- 6 N) qPCR analysis for SOX2 and NKX2-1 in response to these patterning conditions. ( 6 O- 6 T) Doxycycline-induced expression of exogenous SOX2 in ventral cultures on day 8 and analysis on day 9. ( 60 - 6 R) IF staining of cultures for NKX2-1 and HA-SOX2; and ( 6 S- 6 T) qPCR analysis for SOX2 and NKX2-1 in response to patterning conditions. Scale bar=50 μm for IF images, and 200 μm for  Xenopus  explant images. See quantification and statistical analysis section for details. 
         FIGS. 7A-7L . Sox2 regulates expression of secreted Wnt antagonists and Wnt signaling activity in the dorsal foregut endoderm. ( 7 A) Clustered heatmap of differentially expressed genes from RNA sequencing of day 9 dorsal (+Noggin) or ventral (+BMP4) AFG cultures with (+dox) and without SOX2 CRISPR interference (CRISPRi). ( 7 B) Venn diagram analysis of genes upregulated in dorsal and ventral cultures compared to genes that are elevated or decreased following SOX2 knockdown by CRISPRi. ( 7 C) Gene ontology (GO) term analysis on biological processes for genes positively regulated by SOX2. ( 7 D) Number of genes enriched in dorsal and ventral cultures and whether their expression was SOX2-dependent. ( 7 E) Gene set enrichment analysis of the gene ontology term “Regulation of Wnt signaling pathway”, red indicating higher expression while blue indicates low expression. ( 7 F- 7 G) In situ hybridization for the Wnt-responsive gene Axin2 on E9.5 mouse anterior foreguts in ( 7 F) control (Sox2 fl/fl ) and ( 7 G) Sox2-DE-LOF (FoxA2 CreER ; Sox2 fl/fl ) embryos. ( 7 H- 7 I) In situ hybridization for Axin2 in E10.5 mouse embryonic foregut of ( 7 H) control (Sox2 fl/+ ) and ( 7 I) Sox2 cKO (Sox2 CreER/fl ) embryos taken from dams gavaged at 8.5 dpc. Numbers of embryos analyzed is shown in the upper left. Boxed regions ( 7 F- 7 I) highlight the dorsal foregut region. ( 7 J) qPCR analysis for AXIN2 in day 9 dorsal and ventral foregut cultures with or without SOX2 exogenously expressed. ( 7 K) Plotted TPM values for Wnt antagonists SFRP1, SFRP2, and DKK1 from RNA-seq of AFG cultures. ( 7 L) Proposed model on role of Sox2 in dorsal-ventral patterning of the anterior foregut. Scale bar=100 μm. See materials and methods &amp; quantification and statistical analysis section for details. See also  FIG. 14A-14D . 
         FIGS. 8A-8V . Modulating the duration of Wnt and retinoic acid signaling to coordinate foregut patterning across the anterior-posterior axis. ( 8 A) Schematic depicting the experimental protocol to pattern foregut spheroids along the anterior-posterior axis using CHIR99021 (chiron, or chr) and retinoic acid (RA). ( 8 B- 8 G) qPCR analysis of day 6 spheroids resulting from varying the duration of chiron treatment with or without retinoic acid treatment for (B) the anterior and posterior foregut marker HNF1B, ( 8 C- 8 D) the posterior foregut markers PROX1 and HNF6, ( 8 E) the hindgut marker CDX2, ( 8 F- 8 G) and the pharyngeal markers PAX9 and OTX2. ( 8 H- 8 N) A comparison of chiron versus Wnt3a treatment on endoderm by qPCR analysis of ( 8 H) the foregut marker SOX2, ( 8 I) HNF1B, PROX1, HNF6, and CDX2, ( 8 J) Wnt target genes AXIN2, LEF1, and TCF1, and ( 8 K) epithelial and neural marker CDH1 and NESTIN, respectively. Spheroids generated with one day of chiron treatment have same gene expression profile as those generated with 2 days of Wnt3a. ( 8 L- 8 N) Brightfield imaging of nascent spheroids resulting from chiron versus Wnt3a treatments show that the efficiency of generating spheroids is unaffected in the different conditions. ( 8 O- 8 R) Analysis of day 9 spheroids resulting from altering the duration of retinoic acid treatment starting on day 5. qPCR analysis of (80) retinoic acid targets HOXA1, HOXB1, CYP26C1. ( 8 S) Schematic depicting experimental protocol for modulating retinoic acid signaling using the synthesis inhibitor DEAB. ( 8 T- 8 U) qPCR analysis of ( 8 T) foregut markers at day 6, ( 8 U) dorsal anterior foregut markers SOX2 and TP63 (ΔN isoform) at day 9, and ( 8 V) RA targets HOXA1 and HOXB1 at day 9. Scale bar=500 μm in ( 8 L- 8 N) and 50 μm in ( 8 P- 8 R). Error bars indicate SD. *p&lt;0.05, **p&lt;0.01, and ***p&lt;0.001 for two-tailed t-test. 
         FIGS. 9A-9R . Early modulation of Wnt and retinoic acid signaling affects later differentiation into human esophageal organoids. ( 9 A) Schematic depicting the experimental protocol to generate organoids starting with foregut spheroids treated with chiron for 1 or 3 days. ( 9 B- 9 C) qPCR analysis of day 35 (1-month-old) organoids for ( 9 B) stratified squamous epithelial markers KRT5, KRT13, and KRT13, and ( 9 C) posterior foregut markers GATA4 and PDX1. ( 9 D- 9 C) Analysis of day 35 (1-month-old) organoids resulting from altering the duration of retinoic acid treatment starting on day 5. qPCR analysis of ( 9 D) anterior foregut basal transcription factors SOX2 and AN isoform of TP63, ( 9 E) antral stomach and pancreas marker PDX1, and ( 9 F) stratified squamous epithelial markers KRT5, KRT13, and IVL. Immunofluorescence analysis of one-month old organoids with ( 9 G- 9 I) SOX2 and p63, ( 9 J- 9 L) KRT13, and ( 9 M- 9 O) PDX1. ( 9 P) Schematic depicting experimental protocol for modulating retinoic acid signaling using the synthesis inhibitor DEAB. ( 9 Q- 9 R) qPCR analysis of day 35 organoids of ( 9 Q) esophageal basal markers SOX2 and TP63, ( 9 R) stratified squamous epithelial markers KRT5, KRT13, and IVL. These data is representative of 2 separate experiments with n=3 wells in each experiment. Scale bar=100 μm. Error bars indicate SD. *p&lt;0.05 and **p&lt;0.01 for two-tailed t-test. 
         FIGS. 10A-10J . TGFβ inhibition is not required to pattern foregut into anterior foregut spheroids in these culture conditions. ( 10 A) Schematic depicting the experimental protocol to test the requirement of TGFβ signaling in anterior-posterior patterning of the foregut. ( 10 B- 10 F) qPCR analysis on day 6 anterior foregut spheroids treated with and without Wnt3a and TGFβ inhibitor (SB431542, 10 μM) treatment for ( 10 B- 10 C) foregut marker SOX2 and hindgut marker CDX2, ( 10 D) foregut marker HNF1B, and ( 10 E- 10 F) posterior foregut markers PROX1 and HNF6. ( 10 G) Schematic depicting the experimental protocol to test the competency of anterior foregut spheroids treated with and without Wnt3a or the TGFβ inhibitor SB431542 to respond to respiratory induction. (H-J) Analysis of day 9 spheroids for NKX2-1 by ( 10 H- 10 I) immunofluorescence and ( 10 J) qPCR. Scale bar=50 μm. Error bars indicate SD. *p&lt;0.05 and **p&lt;0.01 for two-tailed t-test. 
         FIGS. 11A-11CC . Robust outgrowth of human esophageal organoids and a comparison to mouse embryonic esophageal development. ( 11 A- 11 E) Improved spheroid outgrowth efficiency of organoids treated with FGF10 from day 6-13 as analyzed by (A-D) brightfield imaging and ( 11 E) quantification of the images. ( 11 F- 11 Q) Comparative analysis by immunofluorescence staining of mouse embryonic esophagi at E12.5 ( 11 F,  11 J,  11 N) and E14.5 ( 11 G,  11 K,  11 O) and human esophageal organoids (HEOs) at 2 weeks ( 11 H,  11 L,  11 P) and 3 weeks ( 11 I,  11 M,  11 Q). (R11) Gene expression of stratified squamous epithelial markers in mouse esophagi across time; public data acquired from GEO dataset GSE34728 (Chen et al. 2012). ( 11 S) qPCR analysis of various time points during differentiation of definitive endoderm to human esophageal organoids for stratified squamous epithelial markers. ( 11 T) Quantification of day 62 HEOs for % area of epithelia positive for KRT5 and KRT13. Each point is an individual organoid, and subpanels “a” and “b” are representative images of different organoids depicted in this graph. ( 11 U) Quantification of day 62 HEOs for % epithelial nuclei positive for SOX2 and p63. Each point is an individual organoid. ( 11 V- 11 CC) Immunofluorescence analysis of 1-month old HEOs across different cell lines tested, examining esophageal enriched markers SOX2 and p63 ( 11 V- 11 Y), and KRT13 ( 11 Z- 11 CC). Scale bar=500 μm in ( 11 A- 11 D), 50 μm in ( 11 F- 11 Q,  11 V- 11 CC), and 100 μm in ( 11 T- 11 U). Error bars indicate SD. *p&lt;0.05, **p&lt;0.01, and ***p&lt;0.001 for two-tailed t-test. 
         FIGS. 12A-12R . Alternate methods of human esophageal organoid maturation and expansion. ( 12 A- 12 F) Analysis of HEOs grown for 2 months after transplantation into immunodeficient mice&#39;s kidney capsules by ( 12 A- 12 E) Immunofluorescence images for early (KRT8) and differentiated (KRT13, KRT14, and IVL) esophageal specific markers, and ( 12 F) H&amp;E. ( 12 G- 12 R) Analysis of HEOs mechanically passaged (dissociated and re-cultured) twice. ( 12 G- 12 N) IF images of passaged organoids for ( 12 G- 12 H) transcription factors SOX2 and p63, ( 12 I- 12 J) immature (KRT8) and basal marker (KRT14), ( 12 K- 12 L) basal (KRT5) and suprabasal (KRT13) markers, and ( 12 M- 12 N) suprabasal differentiated markers KRT4, CRNN, and IVL. ( 12 O- 12 R) qPCR analysis comparing passaged HEOs to normal HEOs and gastric organoids (hAGO) for ( 12 O) transcription markers SOX2 and TP63, ( 12 P) stratified squamous markers KRT5, KRT13, IVL, and ( 12 Q- 12 R) patterning markers for lung (NKX2-1), stomach (GATA4), and intestine (GATA4 and CDX2). *p&lt;0.05, **p&lt;0.01, and ***p&lt;0.001 for two-tailed t-test. 
         FIGS. 13A-13V . Post-gastrulation endodermal or broad Sox2 knockout results in a similar phenotype of esophageal agenesis. ( 13 A- 13 B) Wholemount immunofluorescence (IF) analysis for dorsal marker Sox2 (red), respiratory marker Nkx2-1 (green) in E9.5 control (Sox2 fl/fl ) and Sox2-DE-LOF (FoxA2 CreER ; Sox2 fl/fl ) embryos. ( 13 C- 13 D) Wholemount IF analysis for Sox2, Nkx2-1 in E10.5 control (Sox2 fl/fl ) and Sox2-DE-LOF (FoxA2 CreER ; Sox2 fl/fl ) embryos. White arrowheads highlight normal versus ectopic Nkx2-1 expression. ( 13 E- 13 F) IF analysis of foregut sections of E11.5 embryos for the apical marker aPKC (green). (G-H) Wholemount IF analysis for Nkx2-1 of E11.5 control (Sox2 fl/+ ) and Sox2-cKO (Sox2 CreER/fl ) embryos taken from dams gavaged at 8.5 dpc. ( 13 I- 13 L) Immunofluorescence analysis of E11.5 embryos (similar as in  13 E- 13 F) for ( 13 I- 13 J) Sox2 and Nkx2-1, and ( 13 K- 13 L) Sox2 and p63. ( 13 M- 13 T) IF analysis of E10.5 control (Sox2 fl/+ ) and Sox2-cKO (Sox2 CreER/fl ) embryos taken from dams gavaged at 8.5 dpc for epithelial morphology across the anterior ( 13 M,  13 N) to posterior ( 13 S,  13 T) axis. ( 13 S,  13 T) Quantification of ( 13 U) cleaved Caspase 3 and ( 13 V) Ki67 IF staining in E10.5 mouse embryonic foregut for cell death at the point of segregation of the dorsal and ventral foreguts in control (Cre-, Sox2 fl/+ ) and Sox2 cKO (Cre+, Sox2 CreER/fl ) embryos taken from dams gavaged at 8.5 dpc. Scale bar=100 μm for ( 13 A- 13 D,  13 G- 13 H), 50 μm for ( 13 I- 13 T), and 25 μm for ( 13 E- 13 F). For Sox2-DE-LOF embryos, n=3 embryos of each genotype at E9.5, and n=2 embryos for each analysis for each genotype at E11.5 (a minimum of 2 litters were harvested for each analysis and time point). For Sox2-driven Sox2 cKO embryos, n=3 embryos for each genotype. Error bars indicate SD. *p≤0.05 for two-tailed t-test. fg=foregut, dfg=dorsal foregut, vfg=ventral foregut, ph=pharyngeal endoderm, eso=esophagus, r=respiratory progenitor, thy=thyroid, tr=trachea, br=bronchi, st=stomach. 
         FIGS. 14A-14D . Analysis of loss or gain of function on Sox2 in human cultures. ( 14 A) Principal component analysis of the transcriptome resulting from day 9 anterior foregut cultures patterned along the dorsal-ventral axis with and without SOX2 (without or with Dox treatment to activate the CRISPR interference construct). Dorsal vs. ventral anterior foregut (dAFG vs. vAFG) is indicated as chr+Nog and chr+BMP4, respectively. Knockdown is indicated by the +Dox. ( 14 B) TPM values for SOX2 and NKX2-1. ( 14 C) qPCR analysis for SFRP2 on day 9 anterior foregut cultures patterned along the dorsal (dAFG) and ventral (vAFG) axis, including inducing exogenous HA-tagged SOX2 in ventral cultures by Dox treatment on day 8. ( 14 D) Genome browser view of Sox2 peaks at the SFRP2 locus in hPSC-derived endoderm (GSM1505764) and mesendoderm (GSM1505767) from GEO dataset GSE61475 (Tsankov et al., 2015). Scale bar=500 μm. Error bars indicate SD. *p≤0.05 for two-tailed t-test. 
         FIGS. 15A-15E . The role of Sox2 in the development of the esophagus after anterior foregut separation. ( 15 A) Schematic of mouse breeding and tamoxifen administration scheme. ( 15 B) Confocal immunofluorescence (IF) images of E14.5 (left), E17.5 (middle), and P7 (right) esophageal sections with pregnant dams gavaged at 11.5 dpc (left), 14.5 dpc (middle), and pups gavaged at P1 (right), respectively. Sections were stained for E-cadherin to visualize the epithelium, Sox2, and Nkx2-1 for respiratory identity. ( 15 C) IF images of E17.5 esophagus from pregnant dams gavaged at 11.5 dpc for various markers: p63 and Sox2 to confirm esophageal identity, the basal marker Krt14, the suprabasal marker Krt13, the immature or columnar marker Krt8, the proliferation marker Ki67. The green arrowhead in the bottom middle right panel highlights suprabasal Ki67 staining ( 15 D) High magnification IF image of E17.5 esophagus from pregnant dams gavaged at 11.5 dpc for E-cadherin. ( 15 E) IF images of E17.5 esophagus from pregnant dams gavaged at 11.5 dpc for patterning markers: the intestinal marker Cdx2, the gastric/intestinal markers Gata4 and Pdx1, the respiratory marker Nkx2-1, and smooth muscle marker Desmin. The yellow arrowhead highlights the rare Nkx2-1 positive cells in the mutant esophagus. Scale bar=100 μm in ( 15 B,  15 C,  15 E), and 25 μm in ( 15 D). 
         FIGS. 16A-16G . Modeling the effects of Fanconi anemia (FANCA loss) in HEOs. ( 16 A) Schematic depicting the experimental protocol to generate HEOs with (+dox) or without FANCA. **Note: Hydroxyurea (HU) is used for Western blot analysis in ( 16 E). ( 16 B) IF images of day 6 AFG monolayer stained for the foregut marker SOX2 (green) and hindgut marker CDX2 (red). ( 16 C) Brightfield images of HEOs grown with or without doxycycline treatment at week 0 (day 6), week 2 (day 20), and week 4 (day 35) of organoid growth. ( 16 D) IF images of HEOs for SOX2 and the proliferation marker KI67. ( 16 E) Western blot analysis for FANCA and FANCD2 to confirm expression and function of dox-induced FANCA protein. ( 16 F) Size quantification of 2-week-old HEOs from brightfield images. ( 16 G) Quantification of proliferative (KI67+) epithelial cells in 1 month (day 36) old HEOs. Scale bar=100 μm for ( 16 B,  16 D), and 250 μm in ( 16 C). *p≤0.05 and **p≤0.01 for Mann-Whitney non-parametric test. DE=definitive endoderm; AFG=anterior foregut; HEO=human esophageal organoid. 
         FIGS. 17A-17L . Induction of CDX2 in human foregut and HEO cultures. ( 17 A) Schematic depicting the experimental protocol to induce CDX2 in foregut and HEO cultures. ( 17 B) Schematic of the transduced lentiviral vector to induce CDX2 upon administration of doxycycline. ( 17 C) IF analysis of day 6 anterior foregut monolayers treated with various levels of doxycycline (20, 100, and 500 ng/mL) for the foregut marker SOX2 and hindgut marker CDX2. ( 17 D+ 17 E) Quantification of IF images (as in  17 C) by ( 17 D) scatter plot for SOX2 versus CDX2 intensity. Vertical line within scatter plot is the “gate” to define CDX2+ versus CDX2− cells. ( 17 E) Bar graph of percent CDX2+ cells. ( 17 F) IF analysis of 1-month HEOs treated with or without doxycycline for the stratified squamous markers SOX2 and p63, and hindgut (induced) marker CDX2. ( 17 G- 17 L) qPCR analysis of hindgut markers ( 17 G) CDX1, ( 17 H) CDX2, ( 17 I) CDH17, ( 17 J) MUC2, and foregut/stratified squamous markers ( 17 K) SOX2 and ( 17 L) p63. Scale bar=100 μm. **p≤0.01, ***p≤0.001, and ****p≤0.0001 for Student&#39;s t-test with 2-tailed distribution not assuming equal variance. DE=definitive endoderm; FG=foregut; AFG=anterior foregut; HEO=human esophageal organoid. 
         FIGS. 18A-18I .  18 A) Late induction of CDX2 in HEOs result in repression of esophageal transcription factors SOX2 and p63.  18 A. Schematic depicting experimental protocol to induce CDX2 in more mature HEOs (6-7 weeks old).  18 B IF images of day 58 HEOs with (+CDX2) or without doxycycline treatment for stratified squamous markers SOX2 and p63 and hindgut marker CDX2. ( 18 C- 18 E) qPCR analysis of day 58 HEOs for ( 18 C) CDX2, ( 18 D) SOX2, and ( 18 E) p63. ( 18 F) Analysis of IF images (such as  18 B) by scatter plot of HEO basal epithelial cells for CDX2 versus p63 intensity. Vertical line divides the p63-negative (left) and p63 positive (right) cells. Horizontal lines divide the CDX2-negative (bottom), CDX2-low (middle), and CDX2-high (top) cells ( 18 G- 18 I) Quantification of IF analysis (see  18 B and  18 F) for ( 18 G) all CDX2-high and CDX2-low basal cells ( 18 H) CDX2-high and CDX2-low basal cells that are SOX2+, ( 18 I) CDX2-high and CDX2-low basal cells that are p63+. Scale bar=100 um. ***p≤0.0001 for Student&#39;s t-test with 2-tailed distribution not assuming equal variance. DE=definitive endoderm; AFG=anterior foregut; dAFG=dorsal anterior foregut; HEO=human esophageal organoid. 
         FIGS. 19A-19H . Loss of esophageal differentiation in CDX2-induced HEOs. ( 19 A) Schematic of the experimental protocol to induce CDX2 with or without Notch inhibition in HEOs. ( 19 B- 19 G) qPCR analysis of d58 HEOs for the stratified squamous markers ( 19 B) KRT5, ( 19 C) KRT13, and ( 19 D) IVL, ( 19 E) the intestinal epithelial marker CDH17, ( 19 F) the Notch target HESS, and ( 19 G) the BMP target ID1. ( 19 H) IF images of HEOs treated with doxycycline and γ-secretase (Notch) inhibitor DAPT for CDH17, KRT5, and KRT13 (top row); and the differentiated stratified squamous markers CRNN and IVL (bottom row). Scale bar=100 μm. *p≤0.05, **p≤0.01, and ***p≤0.001 for Student&#39;s t-test with 2-tailed distribution not assuming equal variance. DE=definitive endoderm; AFG=anterior foregut; dAFG=dorsal anterior foregut; HEO=human esophageal organoid. 
         FIGS. 20A-20H . IL-13 treated HEOs upregulate IL-13 target genes and increase proliferation. ( 20 A) Schematic depicting the experimental protocol to treat IL-13 in late stage HEOs. ( 20 B- 20 E) qPCR analysis of day 62 HEOs treated with IL-13 for 2 days prior to harvest for known IL-13 target genes ( 20 B) CCL26, ( 20 C) CDS26, ( 20 D) CAPN14, and ( 20 E) SERPINB4. ( 20 F) Western blot analysis of day 50 HEOs treated with IL-13 (100 ng/mL) for 1 week prior to harvest for SERPINB13, CDH26, and a housekeeping protein GAPDS. ( 20 G) IF images of day 62 HEOs treated with IL-13 (100 ng/mL) for 2 weeks and EdU (10 uM) for 2 days prior to harvest. ( 20 H) quantification (of  20 G) for the percent EdU labeled of all basal-most p63 cells. For qPCR data, *p≤0.05 and **p≤0.01 for Student&#39;s t-test with 2-tailed distribution not assuming equal variance. For organoid EdU incorporation quantification, *p&lt;0.05 for Mann-Whitney non-parametric test. Scale bar=100 μm. DE=definitive endoderm; AFG=anterior foregut; HEO=human esophageal organoid. 
         FIGS. 21A-L . Impaired differentiation and altered morphology of HEOs treated with IL-13. ( 21 A) IF analysis of day 62 HEOs treated with IL-13 (100 ng/mL) for 2 weeks prior to harvest. ( 21 B) Western blot analysis of day 56 HEOs treated with IL-13 (100 ng/mL) for 1 week prior to harvest for structural and differentiated proteins. ( 21 C- 21 F) qPCR analysis of day 62 HEOs treated with IL-13 (100 ng/mL) for 2 weeks prior to harvest for ( 21 C) IVL, ( 21 D) CRNN, and the BMP antagonists ( 21 E) NOG and ( 21 F) FST. ( 21 G) Structural analysis of day 62 HEOs treated with IL-13 (100 ng/mL) for 2 weeks prior to fixation by H&amp;E staining (left column) and electron micrographs (right column) ( 21 H- 21 L) qPCR analysis of day 62 HEOs treated with IL-13 (100 ng/mL) and BMP4 (100 ng/mL) for ( 21 H) SOX2, ( 21 I) CCL26, ( 21 J) CDH26, ( 21 K) the hedgehog target PTCH1, and ( 21 L) the BMP target ID3. Scale bar=100 μm for IF and H&amp;E images, and 6 μm for electron micrographs. *p≤0.05, **p≤0.01, ***p≤0.001, and ****p≤0.0001 for Student&#39;s t-test with 2-tailed distribution not assuming equal variance. 
         FIGS. 22A-22H . SOX2-induction in human intestinal organoids (HIOs) upregulate stratified squamous markers. ( 22 A) Schematic depicting experimental protocol to induce SOX2 in HIOs. ( 22 B) Schematic of the transduced lentiviral vector to induce HA-tagged SOX2 upon administration of doxycycline ( 22 C) IF images of day 36 HIOs treated with or without doxycycline for (top) the foregut marker SOX2 and hindgut marker CDX2 (middle) anterior foregut marker p63, gastric/intestinal marker PDX1, and the HA-tag; (bottom) the intestinal marker CDH17 and gastric marker CLDN18 ( 22 D- 22 H) qPCR analysis for various regional markers ( 22 D) SOX2, ( 22 E) p63, ( 22 F) PDX1, and ( 22 G) CDX2, and ( 22 H) the suprabasal stratified squamous marker KRT13. Scale bar=100 um. *p≤0.05, **p≤0.01, and ****p≤0.0001 for Student&#39;s t-test with 2-tailed distribution not assuming equal variance. DE=definitive endoderm; HG=hindgut; HIO=human intestinal organoid. 
         FIGS. 23A-23J . BMP activation in HEOs result in loss of proliferation and differentiation. ( 23 A) Schematic depicting the experimental protocol to activate BMP signaling in late stage HEOs. ( 23 B) IF images of day 62 HEOs treated with or without BMP4 (100 ng/mL) for: (left) pSMAD1/5/9 and SOX2, (middle) p63 and EdU, (right) IVL and CRNN. ( 23 C) Quantification for the percent EdU labeled of all basal-most epithelial cells in HEOs with or without BMP4. ( 23 D- 23 J) qPCR analysis of day 62 HEOs for various markers: (D) SOX2, ( 23 E) p63, ( 23 F) ID3, ( 23 G) KRT5, ( 23 H) KRT13, ( 23 I) IVL, and ( 23 J) CRNN. Scale bar=100 μm. For qPCR data, *p≤0.05 and ****p≤0.0001 for Student&#39;s t-test with 2-tailed distribution not assuming equal variance. For organoid EdU incorporation quantification ( 23 C), **p≤0.01 for Mann-Whitney non-parametric test. DE=definitive endoderm; AFG=anterior foregut; dAFG=dorsal anterior foregut; HEO=human esophageal organoid. 
     
    
    
     DETAILED DESCRIPTION 
     Definitions 
     Unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein may be used in practice or testing of the present invention. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting. 
     As used herein and in the appended claims, the singular forms “a,” “and,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a method” includes a plurality of such methods and reference to “a dose” includes reference to one or more doses and equivalents thereof known to those skilled in the art, and so forth. 
     The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, e.g., the limitations of the measurement system. For example, “about” may mean within 1 or more than 1 standard deviation, per the practice in the art. Alternatively, “about” may mean a range of up to 20%, or up to 10%, or up to 5%, or up to 1% of a given value. Alternatively, particularly with respect to biological systems or processes, the term may mean within an order of magnitude, preferably within 5-fold, and more preferably within 2-fold, of a value. Where particular values are described in the application and claims, unless otherwise stated the term “about” meaning within an acceptable error range for the particular value should be assumed. 
     The terms “individual,” “host,” “subject,” and “patient” are used interchangeably to refer to an animal that is the object of treatment, observation and/or experiment. Generally, the term refers to a human patient, but the methods and compositions may be equally applicable to non-human subjects such as other mammals. In some embodiments, the terms refer to humans. In further embodiments, the terms may refer to children. 
     As used herein, the term “definitive endoderm (DE) cell” means one of the three primary germ layers produced by the process of gastrulation. 
     As used herein the term “wnt signalling pathway” means the wnt/beta-catenin pathway and is a signal transduction pathway that is mediated by Wnt ligands and frizzled cell surface receptors that acts through the beta-catenin protein. 
     As used herein the term “activator” with respect to a pathway, such as a “wnt pathway” means a substance that activates the Wnt/beta-catenin pathway such that Wnt/beta-catenin targets are increased. 
     As used herein, the term “FGF signaling pathway activator” means a substance that activates the FGF pathway such that FGF targets are increased. 
     As used herein, the term “BMP signaling pathway inhibitor” a substance that interferes with the BMP pathway and causes BMP targets to be decreased. 
     As used herein, the term “growth factor” means a substance capable of stimulating cellular processes including but not limited to growth, proliferation, morphogenesis or differentiation. 
     As used herein, the term “stable expression” of a marker means expression that does not change upon modification of the growth environment. 
     As used herein, the term “totipotent stem cells” (also known as omnipotent stem cells) are stem cells that can differentiate into embryonic and extra-embryonic cell types. Such cells can construct a complete, viable, organism. These cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg are also totipotent. 
     As used herein, the term “pluripotent stem cells (PSCs),” also commonly known as PS cells, encompasses any cells that can differentiate into nearly all cells, i.e., cells derived from any of the three germ layers (germinal epithelium), including endoderm (interior stomach lining, gastrointestinal tract, the lungs), mesoderm (muscle, bone, blood, urogenital), and ectoderm (epidermal tissues and nervous system). PSCs can be the descendants of totipotent cells, derived from embryos (including embryonic germ cells) or obtained through induction of a non-pluripotent cell, such as an adult somatic cell, by forcing the expression of certain genes. 
     As used herein, the term “induced pluripotent stem cells (iPSCs),” also commonly abbreviated as iPS cells, refers to a type of pluripotent stem cells artificially derived from a normally non-pluripotent cell, such as an adult somatic cell, by inducing a “forced” expression of certain genes. 
     As used herein, the term “precursor cell” encompasses any cells that can be used in methods described herein, through which one or more precursor cells acquire the ability to renew itself or differentiate into one or more specialized cell types. In some embodiments, a precursor cell is pluripotent or has the capacity to becoming pluripotent. In some embodiments, the precursor cells are subjected to the treatment of external factors (e.g., growth factors) to acquire pluripotency. In some embodiments, a precursor cell can be a totipotent stem cell; a pluripotent stem cell (induced or non-induced); a multipotent stem cell; and a unipotent stem cell. In some embodiments, a precursor cell can be from an embryo, an infant, a child, or an adult. In some embodiments, a precursor cell can be a somatic cell subject to treatment such that pluripotency is conferred via genetic manipulation or protein/peptide treatment. 
     In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. As used herein, the term “directed differentiation” describes a process through which a less specialized cell becomes a particular specialized target cell type. The particularity of the specialized target cell type can be determined by any applicable methods that can be used to define or alter the destiny of the initial cell. Exemplary methods include but are not limited to genetic manipulation, chemical treatment, protein treatment, and nucleic acid treatment. 
     As used herein, the term “cellular constituents” are individual genes, proteins, mRNA expressing genes, and/or any other variable cellular component or protein activities such as the degree of protein modification (e.g., phosphorylation), for example, that is typically measured in biological experiments (e.g., by microarray or immunohistochemistry) by those skilled in the art. Significant discoveries relating to the complex networks of biochemical processes underlying living systems, common human diseases, and gene discovery and structure determination can now be attributed to the application of cellular constituent abundance data as part of the research process. Cellular constituent abundance data can help to identify biomarkers, discriminate disease subtypes and identify mechanisms of toxicity. 
     Pluripotent Stem Cells Derived from Embryonic Cells 
     In some embodiments, an important step is to obtain stem cells that are pluripotent or can be induced to become pluripotent. In some embodiments, pluripotent stem cells are derived from embryonic stem cells, which are in turn derived from totipotent cells of the early mammalian embryo and are capable of unlimited, undifferentiated proliferation in vitro. Embryonic stem cells are pluripotent stem cells derived from the inner cell mass of the blastocyst, an early-stage embryo. Methods for deriving embryonic stem cells from blastocytes are well known in the art. Human embryonic stem cells H9 (H9-hESCs) are used in the exemplary embodiments described in the present application, but it would be understood by one of skill in the art that the methods and systems described herein are applicable to any stem cells. 
     Additional stem cells that can be used in embodiments in accordance with the present invention include but are not limited to those provided by or described in the database hosted by the National Stem Cell Bank (NSCB), Human Embryonic Stem Cell Research Center at the University of California, San Francisco (UCSF); WISC cell Bank at the Wi Cell Research Institute; the University of Wisconsin Stem Cell and Regenerative Medicine Center (UW-SCRMC); Novocell, Inc. (San Diego, Calif.); Cellartis AB (Goteborg, Sweden); ES Cell International Pte Ltd (Singapore); Technion at the Israel Institute of Technology (Haifa, Israel); and the Stem Cell Database hosted by Princeton University and the University of Pennsylvania. Exemplary embryonic stem cells that can be used in embodiments in accordance with the present invention include but are not limited to SA01 (SA001); SA02 (SA002); ES01 (HES-1); ES02 (HES-2); ES03 (HES-3); ES04 (HES-4); ES05 (HES-5); ES06 (HES-6); BG01 (BGN-01); BG02 (BGN-02); BG03 (BGN-03); TE03 (13); TE04 (14); TE06 (16); UCO1 (HSF1); UCO6 (HSF6); WA01 (H1); WA07 (H7); WA09 (H9); WA13 (H13); WA14 (H14). 
     More details on embryonic stem cells can be found in, for example, Thomson et al., 1998, “Embryonic Stem Cell Lines Derived from Human Blastocysts,” Science 282 (5391):1145-1147; Andrews et al., 2005, “Embryonic stem (ES) cells and embryonal carcinoma (EC) cells: opposite sides of the same coin,” Biochem Soc Trans 33:1526-1530; Martin 1980, “Teratocarcinomas and mammalian embryogenesis,”. Science 209 (4458):768-776; Evans and Kaufman, 1981, “Establishment in culture of pluripotent cells from mouse embryos,” Nature 292(5819): 154-156; Klimanskaya et al., 2005, “Human embryonic stem cells derived without feeder cells,” Lancet 365 (9471): 1636-1641; each of which is hereby incorporated herein in its entirety. 
     Induced Pluripotent Stem Cells (iPSCs) 
     In some embodiments, iPSCs are derived by transfection of certain stem cell-associated genes into non-pluripotent cells, such as adult fibroblasts. Transfection is typically achieved through viral vectors, such as retroviruses. Transfected genes include the master transcriptional regulators Oct-3/4 (Pouf51) and Sox2, although it is suggested that other genes enhance the efficiency of induction. After 3-4 weeks, small numbers of transfected cells begin to become morphologically and biochemically similar to pluripotent stem cells, and are typically isolated through morphological selection, doubling time, or through a reporter gene and antibiotic selection. As used herein, iPSCs include but are not limited to first generation iPSCs, second generation iPSCs in mice, and human induced pluripotent stem cells. In some embodiments, a retroviral system is used to transform human fibroblasts into pluripotent stem cells using four pivotal genes: Oct3/4, Sox2, Klf4, and c-Myc. In alternative embodiments, a lentiviral system is used to transform somatic cells with OCT4, SOX2, NANOG, and LIN28. Genes whose expression are induced in iPSCs include but are not limited to Oct-3/4 (e.g., Pou5fl); certain members of the Sox gene family (e.g., Sox1, Sox2, Sox3, and Sox15); certain members of the Klf family (e.g., Klf1, Klf2, Klf4, and Klf5), certain members of the Myc family (e.g., C-myc, L-myc, and N-myc), Nanog, and LIN28. 
     In some embodiments, non-viral based technologies are employed to generate iPSCs. In some embodiments, an adenovirus can be used to transport the requisite four genes into the DNA of skin and liver cells of mice, resulting in cells identical to embryonic stem cells. Since the adenovirus does not combine any of its own genes with the targeted host, the danger of creating tumors is eliminated. In some embodiments, reprogramming can be accomplished via plasmid without any virus transfection system at all, although at very low efficiencies. In other embodiments, direct delivery of proteins is used to generate iPSCs, thus eliminating the need for viruses or genetic modification. In some embodiment, generation of mouse iPSCs is possible using a similar methodology: a repeated treatment of the cells with certain proteins channeled into the cells via poly-arginine anchors was sufficient to induce pluripotency. In some embodiments, the expression of pluripotency induction genes can also be increased by treating somatic cells with FGF2 under low oxygen conditions. 
     More details on embryonic stem cells can be found in, for example, Kaji et al., 2009, “Virus free induction of pluripotency and subsequent excision of reprogramming factors,” Nature 458:771-775; Woltjen et al., 2009, “piggyBac transposition reprograms fibroblasts to induced pluripotent stem cells,” Nature 458:766-770; Okita et al., 2008, “Generation of Mouse Induced Pluripotent Stem Cells Without Viral Vectors,” Science 322(5903):949-953; Stadtfeld et al., 2008, “Induced Pluripotent Stem Cells Generated without Viral Integration,” Science 322(5903):945-949; and Zhou et al., 2009, “Generation of Induced Pluripotent Stem Cells Using Recombinant Proteins,” Cell Stem Cell 4(5):381-384; each of which is hereby incorporated herein in its entirety. 
     In some embodiments, exemplary iPS cell lines include but not limited to iPS-DF19-9; iPS-DF19-9; iPS-DF4-3; iPS-DF6-9; iPS(Foreskin); iPS(IMR90); and iPS(IMR90). 
     More details on the functions of signaling pathways relating to DE development can be found in, for example, Zorn and Wells, 2009, “Vertebrate endoderm development and organ formation,” Annu Rev Cell Dev Biol 25:221-251; Dessimoz et al., 2006, “FGF signaling is necessary for establishing gut tube domains along the anterior-posterior axis in vivo,” Mech Dev 123:42-55; McLin et al., 2007, “Repression of Wnt/β-catenin signaling in the anterior endoderm is essential for liver and pancreas development. Development,” 134:2207-2217; Wells and Melton, 2000, Development 127:1563-1572; de Santa Barbara et al., 2003, “Development and differentiation of the intestinal epithelium,” Cell Mol Life Sci 60(7): 1322-1332; each of which is hereby incorporated herein in its entirety. 
     Any methods for producing definitive endoderm from pluripotent cells (e.g., iPSCs or ESCs) are applicable to the methods described herein. In some embodiments, pluripotent cells are derived from a morula. In some embodiments, pluripotent stem cells are stem cells. Stem cells used in these methods can include, but are not limited to, embryonic stem cells. Embryonic stem cells can be derived from the embryonic inner cell mass or from the embryonic gonadal ridges. Embryonic stem cells or germ cells can originate from a variety of animal species including, but not limited to, various mammalian species including humans. In some embodiments, human embryonic stem cells are used to produce definitive endoderm. In some embodiments, human embryonic germ cells are used to produce definitive endoderm. In some embodiments, iPSCs are used to produce definitive endoderm. 
     Tracheal and esophageal disorders are prevalent in humans and are difficult to accurately model in mice. Applicant therefore established a three-dimensional organoid model of esophageal development through directed differentiation of human pluripotent stem cells. Sequential manipulation of BMP, WNT, and RA signaling pathways allowed pattern definitive endoderm into foregut, anterior foregut (AFG), and dorsal AFG spheroids. Dorsal AFG spheroids grown in a 3D matrix formed human esophageal organoids (HEOs), and HEO cells could be transitioned into two-dimensional cultures and grown as esophageal organotypic rafts. In both configurations, esophageal tissues had proliferative basal progenitors and a differentiated stratified squamous epithelium. Using HEO cultures to model human esophageal birth defects, Applicant identified that Sox2 promotes esophageal specification in part through repressing Wnt signaling in dorsal AFG and promoting survival. Consistently, Sox2 ablation in mice causes esophageal agenesis. Thus, HEOs present a powerful platform for modeling human pathologies and tissue engineering. 
     Human tissue organoids, differentiated from pluripotent stem cells (PSCs) or obtained directly from organs, have proven to be excellent models of tissue physiology and pathology (McCauley and Wells, 2017). In general, the process of converting PSCs into organ cell types relies on step-wise differentiation that recapitulates organogenesis, including formation of definitive endoderm (DE), anterior-posterior patterning into foregut, midgut, and hindgut, organ specification, and differentiation into organ specific lineages. This approach has been used to generate human anterior and posterior endoderm organoids including respiratory, gastric, small intestine and colon (Chen et al., 2017; Dye et al., 2015, 2016, McCracken et al., 2014, 2017; Múnera et al., 2017; Spence et al., 2011). However, human PSC-derived esophageal tissues have not been reported. Dual BMP and TGFβ inhibition after DE induction generates anterior foregut (AFG); however, this yielded a mix of tissues including pharyngeal, esophageal and respiratory endoderm (Green et al., 2011; Kearns et al., 2013; Longmire et al., 2012). This suggests that a more refined patterning approach based on pathways that control esophageal development is required to direct differentiation of PSCs specifically into esophagus. 
     Several signaling pathways guide differentiation and morphogenesis of the developing esophagus. The esophageal epithelium derives from definitive endoderm (DE), a 2-dimensional sheet of cells that forms during gastrulation (Zorn and Wells, 2007). The DE then is patterned along the anterior-posterior axis by Wnt, BMP and FGF signaling and forms a primitive gut tube, divided broadly into the foregut, midgut, and hindgut (Dessimoz et al., 2006; McLin et al., 2007; Stevens et al., 2017; Zorn and Wells, 2009). The foregut is further patterned into posterior foregut by retinoic acid (RA) (Bayha et al., 2009; Niederreither et al., 1999; Wang et al., 2006). The anterior foregut (AFG) gives rise to the esophagus and respiratory tract. Respiratory specification in response to Wnt and BMP activation results in expression of the transcription factor Nkx2-1 whereas inhibition of BMP in the dorsal foregut promotes development of Sox2-expressing esophageal epithelium (Domyan et al., 2011; Goss et al., 2009; Harris-Johnson et al., 2009; Que et al., 2006; Rankin et al., 2016). The esophagus starts as a simple cuboidal epithelium but develops into a stratified squamous epithelium that expresses multiple keratin proteins and a basal layer that expresses Sox2 and p63 (Rosekrans et al., 2015; Zhang et al., 2016). 
     Disclosed herein is the temporal manipulation of the above signaling pathways to differentiate human PSCs into esophageal organoids. Following DE formation, Applicant identified that precise temporal manipulation of BMP, WNT, and RA pathways direct formation of AFG spheroids. Consistent with in vivo data, AFG spheroids acquired a respiratory fate through activation of WNT and BMP pathways whereas BMP inhibition promoted formation of dorsal foregut spheroids that upon continued growth for 1-2 months formed human esophageal organoids (HEOs). HEOs contained stratified squamous epithelium, with distinct basal and luminal cell layers, and harbored proliferative esophageal progenitors that could be expanded and differentiated into esophageal epithelium in organotypic raft cultures. HEOs, used in parallel with mouse embryos, can be used to identify molecular pathways that are affected by SOX2 loss-of-function, one cause of esophageal atresia in humans and mice (Domyan et al., 2011; Que et al., 2007). While reduced Sox2 function leads to esophageal atresia in mice, complete loss of Sox2 in mouse foregut endoderm results in esophageal agenesis. Loss of SOX2 function and transcriptional profiling of human and mouse foregut identified that SOX2 regulates the dorsal expression of Wnt antagonists such as SFRP2, suggesting that SOX2 represses the ability of Wnt to induce a respiratory fate in the dorsal foregut. Net, Applicant has found that the disclosed HEOs provide a complementary platform to study human esophageal organogenesis, birth defects, and disease. 
     In one aspect, a method of making an esophageal organoid (EO) is disclosed. The method may comprise the steps of contacting a definitive endoderm with a BMP inhibitor, a Wnt activator, an FGF activator, and retinoic acid (RA). This contacting step may be for a first period of time sufficient to form an anterior foregut culture. In one aspect, the anterior foregut culture expresses SOX2 and HNF1B after such first period of time, and does not substantially express PROX1 and HNF6. The method may further comprise the step of contacting the anterior foregut culture with a BMP inhibitor (Noggin), and an EGF activator for a second period of time sufficient to form a dorsal anterior foregut (“dAFG”) spheroid, wherein the dAFG may express SOX2 and TP63 but not PDX1, PAX9, or NKX2.1. The method may further comprise the step of culturing the dAFG for a third period of time sufficient to allow formation of an esophageal organoid (EO), wherein said culturing is carried out in the presence of EGF, further optionally including an FGF signaling pathway activator, preferably FGF10. In one aspect, the EO is a human esophageal organoid (HEO). 
     Exemplary gene (or mRNA when gene is not available) accession numbers are provided as follows: SOX2 (NG_009080.1); HNF1B (NG_013019.2), PROX1 (NC_000001.11); HNF6 (NM_214659.1); TP63 (NG_007550.1); PDX1 (NG_008183.1), PAX9 (NG_013357.1); and NKX2.1 (NG_013365.1). It is to be noted that the Gene Name as listed above (i.e., “SOX2, HNF1B, etc.) is sufficient for one of ordinary skill in the art to identify the recited gene. The named genes are intended to encompass variations of the gene and are not intended to be limited by the naming of exemplary accession numbers provided. That is, the provided accession numbers are not intended to limit the scope of the gene and/or claims, is but one of many identifiers for these genes/mRNA/protein, and is solely exemplary in nature. That is, the identifiers may only refer to specific isoform/variant which may be one of many. This distinction will be readily appreciated by one of ordinary skill in the art, and one of ordinary skill in the art will appreciate that the recited genes encompass variants and genes having sequences different from that associated with the accession numbers above. 
     In one aspect, the definitive endoderm may be derived from a precursor cell selected from an embryonic stem cell, an embryonic germ cell, an induced pluripotent stem cell, a mesoderm cell, a definitive endoderm cell, a posterior endoderm cell, a posterior endoderm cell, and a hindgut cell. In one aspect, the definitive endoderm may be derived from a pluripotent stem cell. In one aspect, the definitive endoderm may be derived from a pluripotent stem cell selected from an embryonic stem cell, an adult stem cell, or an induced pluripotent stem cell. In one aspect, the DE may be a DE monolayer, wherein greater than 90% of the cells in the DE monolayer co-express FOXA2 and SOX17. 
     In one aspect, the definitive endoderm may be derived from contacting a pluripotent stem cell with one or more molecules selected from Activin, the BMP subgroups of the TGF-beta superfamily of growth factors; Nodal, Activin A, Activin B, BMP4, Wnt3a, and combinations thereof. 
     In one aspect, the BMP signaling pathway inhibitor may be selected from Noggin, Dorsomorphin, LDN189, DMH-1, and combinations thereof. In one aspect, the BMP signaling pathway inhibitor is Noggin. The BMP inhibitor may be present at a concentration of between from about 50 to about 1500 ng/ml. 
     In one aspect, the WNT activator may be selected from one or more molecules selected from the group consisting of Wnt1, Wnt2, Wnt2b, Wnt3, Wnt3a, Wnt4, Wnt5a, Wnt5b, Wnt6, Wnt7a, Wnt7b, Wnt8a, Wnt8b, Wnt9a, Wnt9b, Wnt10a, Wnt10b, Wnt11, Wnt16, a GSKβ inhibitor (e.g., CHIR99021, i.e. “CHIRON”), BIO, LY2090314, SB-216763, lithium, porcupine inhibitors IWP, LGK974, C59, SFRP inhibitor WAY-316606, beta-catenin activator DCA. The concentration of the Wnt pathway activator may be, for example, used at a concentration between about 50 to about 1500 ng/ml. There are many ways to activate the Wnt/beta-catenin pathway (see http://web.stanford.edu/group/nusselab/cgi-bin/wnt/). Suitable Some existing wnt signalling pathway activators include but are not limited to protein-based activators, which may include Wnt ligands including but not limited to Wnt1, Wnt2, Wnt2b, Wnt3, Wnt3a, Wnt8, et al; modifiers of Wnt ligand activity including but not limited to activated Wnt frizzled receptors, (LRP) co-receptors, R-spondin proteins, Dkk proteins, regulators of Wnt ligand secretion and trafficking (Wnt1ess, Porcupine), inhibiting beta-catenin degredation APC and GSK3beta inhibition, activated beta-catenin, constitutively active TCF/Lef proteins and chemical activators, which may include over 28 known chemicals that either activate or inhibit Wnt/beta-catenin signaling. Some activators include but are not limited to GSK3-beta inhibitors CHIR99021 (CHIRON), BIO, LY2090314, SB-216763, lithium, porcupine inhibitors IWP, LGK974, C59, SFRP inhibitor WAY-316606, beta-catenin activator DCA. 
     In one aspect, the FGF activator may be one or more molecules selected from the group consisting of FGF1, FGF2, FGF3, FGF4, FGF10, FGF11, FGF12, FGF13, FGF14, FGF15, FGF16, FGF17, FGF18, FGF19, FGF20, FGF21, FGF22, FGF23, and combinations thereof, preferably FGF4 or FGF10, or a combination thereof. In one aspect, the concentration of the FGF pathway activator may be used at a concentration between about 50 to about 1500 ng/ml. Proteins and chemicals that stimulate the FGF receptor and signaling components downstream of the receptors including MAPK, MEK, ERK proteins and chemicals that modulate their activity. FGF signaling can be activated by inhibiting inhibitors of FGF signaling pathways including but not limited to Sprouty protein family members. 
     In one aspect, the retinoic acid of step a may be contacted with the DE for a period of time of from about 12 hours to about 48 hours, or about 20 hours to about 40 hours, or about 24 hours, or until treatment results in PDX expression and loss of p63 expression. 
     In one aspect, said step c may be carried out for a period of time sufficient for formation of a stratified epithelium lacking KRT8. In one aspect, step c may be carried out for a period of time sufficient for formation a stratified squamous epithelium expressing regional keratins. In one aspect, step c may be carried out for a period of time sufficient for said HEO to express INV. 
     In one aspect, the first period may be a period of about three days ±24 hours. In one aspect, the second period may be a period of about three days ±24 hours. In one aspect, the third period may be a period of about 28 days ±48 hours, or about 21 days to about 90 days, or about 30 days to about 60 days. In one aspect, steps a through c may be conducted in vitro. 
     In one aspect, the method may further comprise the step of contacting the anterior foregut culture of step a) or the spheroid of step b) with a matrix selected from collagen, basement membrane matrix (Matrigel), or a combination thereof. 
     In one aspect, the esophageal compositions described herein may be characterized by being free of innervation and/or blood vessels. In one aspect, the composition is a human esophageal organoid (HEO) composition, wherein the HEO composition is substantially free of one or more of submucosal glands, transition zones, vasculature, immune cells, or submucosal layers. 
     In one aspect, an esophogeal progenitor cell capable of organizing into an organotypic culture is disclosed. The esophageal progenitor cell may be derived from the method disclosed herein. 
     In one aspect, a method of making a stratified squamous epithelium is disclosed. The method may comprise the steps of enzymatically dissociating an HEO as described herein to release progenitor cells, wherein the HEO is at an age of about 3 weeks to about 10 weeks, or about 4 weeks to about 8 weeks, or about 5 weeks of age; expanding said progenitor cells in a monolayer; and re-differentiating the dissociated HEOs into a stratified squamous epithelium on a collagen coated membrane for a period of time sufficient to give rise to a non-keratinized stratified squamous epithelium, wherein the non-keratinized stratified squamous epithelium expresses keratins and one or more markers selected from IVL, CRNN, and FLG. In one aspect, stratified squamous epithelium may comprise esophageal cells organized substantially in the form of a sheet. 
     In one aspect, a method of treating a disease of the esophagus in an individual in need thereof is disclosed. The disease may be selected from a congenital disease (atresia), a functional disease (achalasia and other motility disorders) an immunological disease (eosinophilic esophagitis), pathological disease (Barrett&#39;s esophagus and esophageal carcinoma), and combination thereof, comprising the step of contacting an esophageal composition (such as an HEO or esophageal sheet) as disclosed herein, with said individual. 
     In one aspect, the disease may comprise an ulcer or ulcerated tissue of the esophagus, and the disclosed esophageal compositions may be used to contact and repair the ulcerated tissue. For example, in one aspect, the esophageal composition may comprise esophageal cells organized substantially in the form of a sheet, which may be contacted with the patient. 
     In one aspect, a method of identifying a treatment for eosinophilic esophagitis is disclosed. In this aspect, the method may comprise the step of contacting a potential therapeutic agent of interest with an organoid or esophageal tissue as described herein, detecting a measure of eosinophilic esophagitis activity, and determining whether the potential therapeutic agent of interest improves a measure of eosinophilic esophagitis activity. 
     In one aspect, a method of making a Fanconi&#39;s anemia disease model is disclosed. In this aspect, the disclosed methods of making and HEO or an esophageal sheet are carried out as described herein, wherein the DE is obtained from a precursor cell deficient in FANCA. 
     In one aspect, a method of making a Barrett&#39;s metaplasia disease model is disclosed. In this aspect, the method may comprise the step of inducing CDX2 and activating BMP in an HEO or esophageal sheet made according to the methods disclosed herein. 
     In one aspect, A method of making an eosinophilic esophagitis disease model is disclosed. In this aspect, the method may comprise the step of contacting an HEO or esophageal sheet made according to the methods disclosed herein with IL-13 for a period of time sufficient to increase expression of CCL26 and CAPN14 and decrease expression of CRNN and IVL 
     In one aspect, A method of identifying an active agent capable of treating an esophageal disease state is disclosed. comprising the step of contacting a test agent with an HEO or esophageal sheet made according to the methods disclosed herein for a period of time sufficient to elicit a physiological change in said disease model; and detecting a decrease in expression of CCL26 and CAPN14 and an increase in expression of CRNN and IVL for EoE; or detecting an increase in esophageal gene expression such as SOX2, p63, KRT13, CRNN, IVL and a loss of intestinal genes for Barrett&#39;s. 
     EXAMPLES 
     The following non-limiting examples are provided to further illustrate embodiments of the invention disclosed herein. It should be appreciated by those of skill in the art that the techniques disclosed in the examples that follow represent approaches that have been found to function well in the practice of the invention, and thus may be considered to constitute examples of modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes may be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. 
     Wnt and Retinoic Acid Signaling Control Anterior Versus Posterior Foregut Fate 
     To generate foregut derivatives, hPSCs were first induced into DE and then three-dimensional (3D) SOX2-expressing foregut spheroids as previously described ( FIG. 1 ) (D&#39;Amour et al., 2005; Dye et al., 2016; McCracken et al., 2014, 2017). In attempting to generate esophageal organoids, the primary challenge was to generate foregut tissue of the correct regional identity. Endoderm patterning is regulated by differential BMP, WNT and RA signaling, where the highest levels of activation of these pathways promoting a mid- and hindgut fate and lower levels promoting a foregut fate (Bayha et al., 2009; Davenport et al., 2016; Matt et al., 2003; McLin et al., 2007; Tiso et al., 2002; Wang et al., 2006). Based on our previous studies indicating that the duration of signaling is important for differentiation, Applicant tested the effects of duration of Wnt activation during foregut spheroid formation on anterior-posterior identity (Spence et al., 2011). Applicant found that shorter duration of chiron, a canonical Wnt pathway activator (through GSK3β inhibition), or Wnt3a treatment following DE formation resulted in formation of anterior foregut (AFG) spheroids expressing HNF1β and SOX2, with low levels of posterior foregut markers PROX1 and HNF6 ( FIG. 1A-1E, 8A-8G ). HN1β is not expressed in pharyngeal endoderm indicating that AFG spheroids were not pharyngeal ( FIG. 1C-1E, 8B ). CDX2, a mid/hindgut marker, is not expressed ( FIG. 1B, 1D, 1E ). From this, Applicant concluded that the regional identity of these foregut spheroids (HNF1B+/SOX2+, PROX1−/HNF6−) are distal to the pharynx and proximal to the posterior foregut. 
     Four days of RA treatment is also known to posteriorize foregut spheroids (McCracken et al., 2014), and loss of RA signaling results in abnormal development of posterior foregut organs (Bayha et al., 2009; Wang et al., 2006). Applicant therefore investigated whether shortening the duration of RA signaling in foregut cultures would promote a more anterior fate. Foregut cultures treated with RA for 4 days express posterior foregut markers, GATA4 and PDX1, whereas 1 day of RA treatment resulted in spheroids that express TP63, a marker expressed in the developing esophagus ( FIG. 1F-K ,  8 O- 8 R). Cultures lacking RA, or containing DEAB, an aldehyde dehydrogenase inhibitor (blocking RA synthesis) yielded spheroids with minimal TP63 expression and increased levels of the pharyngeal markers PAX9 and OTX2 ( FIG. 1G-1K, 8F-8G ;  8 S- 8 V). Together, the data suggests that brief activation of RA promotes foregut regional identity consistent with the presumptive esophageal domain. 
     Anterior Foregut Spheroids are Competent to Form Esophagus or Respiratory Lineages. 
     The presumptive esophageal/respiratory region of the foregut is patterned along the dorsal-ventral (D-V) axis, resulting in specification of the esophageal and respiratory fates respectively. Applicant predicted that AFG spheroids would respond to D-V patterning cues to acquire either an esophageal or respiratory fate. Studies in vertebrate embryos demonstrate that BMP and Wnt signaling promote a respiratory fate (NKX2-1+SOX2−), while Noggin-mediated inhibition of BMP signaling in the dorsal foregut tube is required for esophageal development (Domyan et al., 2011; Fausett et al., 2014; Goss et al., 2009; Harris-Johnson et al., 2009; Que et al., 2006). Thus, Applicant treated day 6 AFG spheroids with either 3 days of chiron and BMP4 or alternatively with Noggin (to inhibit BMP signaling) ( FIG. 2A-2B ). Treatment with chiron+BMP4 resulted in induction of NKX2-1 and repression of SOX2, whereas treatment with Noggin dorsalized spheroids, as marked by elevated levels of SOX2, MNX1, KRT4, and TP63 ( FIG. 2C-I ) (Daniely et al., 2004; Sherwood et al., 2009). Taken together, inhibition of BMP signaling in cultures of AFG spheroids promoted a dorsal anterior foregut identity. 
     Formation of Esophageal Organoids with a Stratified Squamous Epithelium 
     To determine if dorsally-patterned AFG spheroids were competent to grow into esophageal organoids, Applicant cultured them suspended in matrigel with EGF alone or in the context of manipulation of other pathways predicted to promote esophageal development including Wnt activation (chiron), extended BMP inhibition (Noggin), activation of hedgehog (SAG, a smoothened agonist), and FGF10. While most of these manipulations had no effect on growth (data not shown), Applicant found that addition of FGF10 to cultures from day 6 to day 13 resulted in improved efficiency of spheroid to organoid outgrowth ( FIG. 11A-11E ) and did not affect the patterning and differentiation into esophageal organoids (data not shown). 
     Next, Applicant compared the morphologic and molecular development of putative human esophageal organoids (HEOs) to normal development of the embryonic mouse esophagus. During embryonic growth and development, the esophagus transitions from simple cuboidal epithelium at E12.5 to a multilayered/stratified epithelium between E14.5 and E17.5 ( FIG. 3G, 3J, 3M, 3P, 11F-11O, 11R ) (Chen et al., 2012). Similarly, over the course of one month, HEOs expanded in size from approximately 50 μm to 200-400 μm in diameter ( FIG. 3B-3F ). Moreover, the organoid epithelium transitioned from a simple epithelium that was largely SOX2, p63 double-positive to a multilayered epithelium expressing markers of esophageal stratified squamous epithelium ( FIG. 11H-11Q, 11S ). At one month, HEOs expressed basal markers p63 and KRT14 as well as the suprabasal marker KRT13 ( FIG. 3H, 3K, 3N, 3Q ). This expression pattern is similar to an E17.5 esophagus composed of multilayered epithelium ( FIG. 3G, 3J, 3M, 3P ). 
     One-month HEOs were still relatively immature as evidenced by broad SOX2 epithelial expression and expression of KRT8, a marker of immature esophagus ( FIG. 3J, 11L-11M ). Applicant therefore extended the culture period out to 2 months, which resulted in additional growth and formation of a stratified epithelium that lacked KRT8. Applicant observed robust expression of KRT14 throughout the basal layer and KRT13 and IVL throughout the differentiated suprabasal layers, demonstrating the presence of a stratified squamous epithelium ( FIG. 3I, 3L, 3O, 3R ). Histologically, 2-month HEOs had a more defined basal layer as well as squamous cells suprabasally, with no evidence of cornification ( FIG. 4A ). The epithelial morphology of HEOs was easily distinguished from other organoids including gastric (HGO), intestinal (HIO) or colonic organoids, with each organoid having an epithelial morphology that is unique to that organ type (McCracken et al., 2014, 2017; Múnera et al., 2017; Spence et al., 2011). 
     To show that HEOs were human esophageal epithelium, Applicant compared 1 and 2-month HEOs to human esophageal biopsies as well as 1-month HGOs and HIOs by qPCR. Key stratified squamous epithelial markers p63, KRT5, KRT13, IVL, and CRNN were expressed highest in human esophageal biopsies and 2-month HEOs, whereas HGOs and HIOs negligibly expressed these transcripts ( FIG. 3S-3V ). Additionally, Applicant compared the entire transcriptome of HEOs with that of other human epithelial tissues isolated from esophagus, lung, skin, stomach, small intestine, colon, HGOs, and HIOs. Clustering analyses of RNA sequencing data revealed that HEOs are most closely related to human esophagus and EPC2, an esophageal keratinocyte cell line, as opposed to the stomach, small intestine, and colon ( FIG. 3W ). Applicant used principal component analyses to compare HEOs with HIOs and HGOs and found that even one-month HEOs were entirely distinct from the other gastrointestinal organoids ( FIG. 3X ). A comparison of markers of esophagus, skin, stomach, and colon revealed that HEOs were highly similar to human esophagus, reaffirming the qPCR analysis. While there was significant overlap between skin and esophagus, there were also distinct differences including KRT1 in the skin and KRT4 and 13 in the esophagus. Of note, HEOs did not express gastric or intestinal markers TFF2, CLDN18, GATA4, PDX1, CDX2, and CDH17 ( FIG. 3Y ). 
     Given that growth of PSC-derived organoids in vivo has been shown to promote further maturation and function, Applicant utilized three different transplantation-based approaches to study HEOs in vivo. Applicant first engrafted 1-month old HEOs into the kidney capsule of immunodeficient (NSG) mice and allowed them to grow for 8 weeks, which resulted in maturation in a subset of the organoids transplanted (2/5) ( FIG. 12A-12F ). Applicant used two other transplantation approaches that were unsuccessful: seeding HEOs onto biodegradable PEG scaffolds and transplanting them into the fat pad of mice; or engrafting HEOs into the forestomach of NSG mice (data not shown) (Dye et al., 2016). Overall, the generation of spheroids and organoid outgrowth is robust across various ES and iPS lines, with each generation resulting in a large majority of organoids expressing stratified squamous markers (FIG T- 11 CC). Together, the data demonstrates that PSC-derived dorsal foregut spheroids form esophageal organoids with a well-differentiated, non-keratinized stratified squamous epithelium. 
     HEOs Contain Progenitors Capable of Reconstituting a Stratified Squamous Epithelium 
     The esophagus contains basal progenitors that can give rise to all of the differentiated stratified layers (DeWard et al., 2014; Doupe et al., 2012; Kalabis et al., 2008). This property allows esophageal cells to be isolated, expanded in culture, and then re-differentiated into a stratified squamous epithelium. Applicant first tested if HEOs contain esophageal progenitors by enzymatically dissociating 5-week HEOs into single cells, expanding them in monolayer cultures, and then testing their ability to re-differentiate into a stratified squamous epithelium using an organotypic raft culture method (Hoskins et al., 2009). After 14 days of organotypic culture, the HEO-derived keratinocytes gave rise to a non-keratinized stratified squamous epithelium, expressing the appropriate keratins and differentiated markers IVL, CRNN, FLG. ( FIG. 4A-4N ). HEOs, HEO-derived keratinocytes and organotypic raft cultures all expressed high levels of the basal markers p63, KRT5, and KRT14 ( FIG. 40 -Q), whereas organotypic rafts were the most differentiated, expressing CRNN, IVL, KRT13, TMPRSS11A and D at levels comparable to human esophageal biopsies ( FIG. 4R-4U ). However, efforts to expand these progenitors long-term in 3D organoid cultures were unsuccessful. Dissociated organoids re-plated in 3D-matrigel grew over several weeks, maintained patterning (SOX2+p63+), and were passaged (re-dissociated) several times ( FIG. 12G-12H, 12O, 12Q-12R ). However, passaging efficiency diminished over time, and Applicant was unable to induce differentiation or stratification in these passaged organoids ( FIG. 12I-N ,  12 P). This result is similar to esophageal progenitors derived from human esophagus, demonstrating a general inability to culture these cells long-term (Kasagi et al., 2018). 
     Another method to study basal progenitor differentiation is through pulse-chase labeling of proliferating basal progenitors and following labeled cells as they differentiate into stratified layers over time. Applicant labeled proliferating cells in day 40 HEOs by one day treatment of EdU and analyzed them immediately (day 0) or following a chase period for 2, 6, and 13 days post-label ( FIG. 4V-4BB ). EdU labeled cells initially appeared in p63-expressing basal cells, but over time, these cells moved into the suprabasal compartment, lost p63 expression, and were eventually shed into the lumen by 13 days post-label ( FIG. 4W-4BB ). Thus, it is believed that HEOs contain basal progenitors that differentiate and migrate into the stratified layers, similar to esophageal epithelium. 
     Using HEOs and Mouse Genetics to Identify Mechanisms of Esophageal Development 
     While establishing a PSC-derived HEO model system is an important advance, there is a need to demonstrate that HEOs could be used to study human development and disease. Applicant chose to use HEOs, in parallel with two well-established vertebrate model systems, mouse and  Xenopus , to model esophageal birth defects by studying loss-of-function of SOX2. First, Applicant determined the consequences of complete loss of Sox2, since partial loss of SOX2 function in humans and mice leads to partial loss of the esophagus (atresia) (OMIM 206900, Fantes et al., 2003; Que et al., 2007; Williamson et al., 2006). Applicant generated two mouse models to inducibly delete Sox2 in the foregut endoderm prior to initiation of esophageal development (FoxA2 CreER ; Sox2 fl/fl  and Sox2 CreER/fl ) (Arnold et al., 2011; Park et al., 2008; Shaham et al., 2009). In both models, early deletion of Sox2 in the foregut resulted in complete esophageal agenesis, with the foregut region between the pharynx and stomach remaining as one tube lacking p63 and broadly expressing the respiratory marker Nkx2-1 ( FIG. 5C-5F, 13A-13D ). The lung buds were largely similar to control embryos, and cell polarity was unaffected ( FIG. 13E-F ). Deletion of Sox2 after initiation of esophageal development resulted in partial loss of esophageal tissue, with regions of the esophagus being severely hypoplastic at E11.5. In some regions, the esophagus is only 2-3 cells wide, remains a simple cuboidal epithelium, lacks p63 expression, and expresses Nkx2-1 in some cells ( FIG. 5I-5L ). These data suggest that Sox2 function is required for initiating esophageal development whereas loss of Sox2 one day later results in reduced esophageal tissue and identity. 
     To investigate if esophageal agenesis was caused by changes in cell death and proliferation, or merely absence of septation from the common foregut, Applicant analyzed E10.5 embryos at the start of septation. Sox2 CreER/fl  embryos had increased cleaved Caspase 3 staining in the dorsal foregut at the level where separation would normally be occurring, suggesting that cells of the presumptive esophagus were undergoing cell death ( FIG. 5G-5H, 13U ). Proliferation, as marked by Ki67+ cells, was unchanged ( FIG. 13V ). In both control and Sox2 knockout foreguts, there appears to be a point where the epithelium narrows midway along the dorsal-ventral axis, suggesting that the epithelium is attempting to separate into the two tubes regardless of the presence of Sox2 protein ( FIG S6M -T). The results in mouse demonstrate Sox2 is required in the foregut for esophageal development, survival and for restricting Nkx2-1 to the ventral/respiratory domain. 
     BMP-Independent Roles for Sox2 in Repressing Nkx2-1 Expression 
     Applicant next wanted to exploit the in vitro advantages of human and  Xenopus  foregut cultures to mechanistically explore how Sox2 initiates esophageal development. From previous studies, Sox2 is believed to repress respiratory (ventral) development and promote esophageal (dorsal) development. In order to promote ventral identity, BMP signaling is believed to repress Sox2 in the ventral foregut, thus allowing for Wnt-mediated induction of Nkx2-1 expression (Domyan et al., 2011). Applicant tested if the sole function of BMP is to inhibit Sox2 by inhibiting Sox2 and then activating Wnt, which is predicted to be sufficient to activate Nkx2-1 in the absence of BMP. Knocking down sox2 using morpholino injections in  Xenopus  endoderm explants and activating canonical Wnt signaling with Bio did not activate nkx2-1 expression in the absence of BMP4 ( FIG. 6A-B ,  6 E- 6 F). However, treatment with Bio and BMP4 expanded the nkx2-1 domain upon sox2 knock down as it was in the mouse Sox2 knockout ( FIG. 6C-6D ). These data suggest two things: one, BMP signaling is required for Nkx2-1 expression independent of Sox2 inhibition; and two, Sox2 is required for repressing ectopic Nkx2-1 expression outside of the respiratory domain. 
     To determine if human SOX2 is required to prevent ectopic expression of NKX2-1, Applicant used an iPSC line to inducibly express a repressor form of CRISPR protein that represses transcription at the SOX2 locus (CRISPRi-SOX2) (Mandegar et al., 2016). SOX2 knockdown in human dorsal anterior foregut cultures (dAFG) resulted in ectopic expression of NKX2-1 mRNA and protein ( FIG. 6G-6J,6L-6M ). Optimal NKX2-1 induction in ventral anterior foregut (vAFG) was still dependent on the presence of BMP ( FIG. 6K-6N ). To determine if SOX2 expression was sufficient to repress NKX2-1, Applicant generated a stable tet-inducible hPSC line to express HA-tagged SOX2 in the ventral foregut during respiratory induction. Expression of SOX2 in the ventral foregut resulted in significant downregulation of NKX2-1 mRNA and protein ( FIG. 6Q-6T ). Together, these data suggest that BMP has additional functions for respiratory induction and confirm that in all contexts Wnt signaling is required for NKX2-1 expression. In addition, SOX2 expression is sufficient to repress NKX2-1 expression through unknown mechanisms. 
     Sox2 Regulates Expression of Wnt Antagonists During Dorsal-Ventral Patterning 
     The ease of manipulation and scalability of foregut cultures are ideally suited for “omic” approaches. Applicant therefore took an RNA sequencing-based approach to identify genes that are regulated by SOX2 and/or BMP signaling during dorsal-ventral (esophageal-respiratory) patterning. Principal component analysis (PCA) identified that the largest groups of regulated genes were for dorsal-ventral patterning (±BMP4 or Noggin) and for SOX2-regulated genes (±dox-SOX2 CRISPRi) ( FIG. 14A ). Moreover, SOX2 regulates a distinct set of genes in dorsal (Noggin) cultures as compared to ventral (BMP4) cultures, as indicated in the cluster heatmap and in the PCA along principal component axis 1 ( FIG. 7A, 14A ). The use of either BMP4 or Noggin resulted in the expected changes in dorsal-ventral patterning markers, such as upregulation of NKX2-1 and repression of SOX2, MNX1, KRT4, PAX9 in the ventral (BMP-high) cultures. The loss of SOX2, however, resulted in many transcriptional changes in the dorsal foregut and relatively few in the ventral foregut, including increased expression of NKX2-1 and reduced expression of FOXE1, NTN1, and GDNF ( FIG. 7A-7B, 7D, 14B ). 
     Of the dorsal and ventral genes, there were transcripts that changed in response to the CRISPRi-SOX2 (either elevated or reduced) and genes that were not (SOX2-independent). For example, of the 542 genes enriched in the dorsal foregut, 75.6% (410 genes) are SOX2-independent. 17.2% (93 genes) in the dorsal foregut were downregulated upon SOX2 knockdown, referred to by Applicant as “positively regulated by SOX2”. There were 39 transcripts that were elevated in response to SOX2 knockdown, suggesting that these are “negatively regulated by SOX2”. In the ventral cultures, 374 genes are upregulated by BMP treatment, and of these, 38 were decreased and 5 were increased in response to loss of SOX2 ( FIG. 7D ). Not surprisingly, more genes were regulated by SOX2 in the dorsal foregut as ventral SOX2 expression is already significantly downregulated in response to BMP. Applicant used intersectional analysis to identify genes that BMP likely regulates through repression of SOX2 and found 46 genes (12.3%) that are both upregulated by both BMP treatment and SOX2 knockdown (“Genes negatively regulated by SOX2”). Applicant also found 81 genes (14.9%) that are both downregulated by both BMP treatment and SOX2 knockdown (“Genes positively regulated by SOX2”) ( FIG. 7B ). In addition, &gt;80% of BMP-regulated transcripts were unchanged in response to SOX2 knockdown, consistent with the conclusion that BMP has a role in ventral foregut specification independent of SOX2 repression. 
     Performing gene ontology analysis of all 404 unique genes whose expression was reduced in dAFG in response to SOX2 knockdown yielded in many significant gene ontology terms, including two terms involving the Wnt signaling pathway ( FIG. 7C ). Gene set enrichment analysis also found several Wnt signaling components to be significantly altered in response to SOX2 knockdown ( FIG. 7E ). The secreted canonical Wnt signaling inhibitors SFRP1, SFRP2, DKK1, were all downregulated upon SOX2 loss ( FIG. 7E, 7K ). Moreover, over-expression of SOX2 in ventral cultures upregulated SFRP2, which is consistent with published ChIP-seq data in hPSC-derived mesendoderm and endoderm showing a SOX2 binding peak at the SFRP2 locus ( FIG. 14C-14D ) (Tsankov et al., 2015). 
     Since SOX2 positively regulates expression of Wnt antagonists, Applicant hypothesized that SOX2 may inhibit canonical Wnt signaling in the dorsal foregut. To investigate this, Applicant deleted Sox2 from the mouse foregut using two genetic models, Foxa2 CreER ; Sox2 fl/fl  and Sox2 CreER/fl  and measured canonical Wnt/β-catenin activity by analyzing expression of the Wnt target gene Axin2 (Jho et al., 2002; Lustig et al., 2002). In situ hybridization revealed high levels of Axin2 mRNA in the ventral foregut endoderm and low levels in the dorsal foregut endoderm of control embryos. In contrast, the dorsal foregut had increased Axin2 staining when Sox2 was deleted ( FIG. 7F-7I ). Similarly, AXIN2 transcript levels were reduced in human ventral foregut cultures with SOX2 exogenously expressed ( FIG. 6G, 7J ). In addition to increased expression of canonical Wnt genes, the Nkx2-1 expression domain was expanded into the dorsal foregut ( FIG. 5E, 13C-13D ). Together with the data from human foregut cultures, Applicant proposes a model in which Sox2 positively regulates expression of secreted Wnt antagonists in the dorsal foregut, which represses canonical Wnt signaling in the dorsal foregut and restricts expression of Nkx2-1 to the ventral foregut. 
     DISCUSSION 
     Generation of HEOs and organotypic raft cultures has been described from primary esophageal cells and cell lines (Andl et al., 2003; Kalabis et al., 2012; Kasagi et al., 2018). In addition, human PSC-derived anterior foregut (AFG) endoderm cultures give rise to a heterogeneous mix of multiple AFG derivatives (Green et al., 2011; Kearns et al., 2013; Longmire et al., 2012). To enrich for esophageal endoderm with this sort of approach, one must rely on cell sorting and subsequent culture, as achieved by Zhang et al. Alternatively, directed differentiation into specific foregut derivatives, like the esophagus, has benefited from a more granular recapitulation of early organ development. Here, Applicant has differentiated human PSCs specifically into HEOs using a step-wise manner approximating DE formation, foregut patterning and morphogenesis, AFG patterning into the presumptive esophageal-respiratory domain, and finally dorsal foregut patterning. This approach gradually restricts endodermal differentiation potential such that one is left with dorsal AFG endoderm that grows out into esophageal organoids. 
     One challenge was to find conditions that generate the respiratory-esophageal anterior region of the foregut but not the anterior-most pharyngeal region. BMP inhibition is essential for foregut specification, and Applicant found that transient Wnt and RA activation patterns foregut into esophageal-respiratory rather than pharyngeal endoderm. Moreover, Applicant found that 1 day of RA promotes expression of TP63 and KRT4 and not posterior foregut markers GATA4 and PDX1. Without intending to be limited by theory, this effect of RA could be direct as RA promotes expression of KRT4 and TP63 in keratinocytes (Bamberger et al., 2002). Due to the lack of specific esophageal markers, Applicant relied on the presence or absence of regionally expressed markers to determine early anterior foregut endoderm identity and exclude pharyngeal, respiratory, hepatic, pancreatic, and gastric endoderm. 
     Applicant also used a functional assay to show that the esophageal-respiratory region of the foregut had been generated. This anterior-posterior level of the foregut should be competent to give rise to the esophagus and respiratory lineage. Applicant showed that AFG spheroids could respond to respiratory-inducing signals (BMP4 and Wnt activation by chiron) by upregulating NKX2-1. Conversely, repression of BMP signaling dorsalizes spheroids based on expression of SOX2, TP63, and MNX1. Interestingly, in Applicant&#39;s culture conditions, addition of a TGFβ inhibitor during foregut induction causes an increase in posterior foregut markers and reduces upregulation of NKX2-1, in contrast to other protocols ( FIG. 10A-J ), exemplifying how timing and combinatorial signaling pathways manipulation can result in different outcomes. 
     The final proof of esophageal lineage commitment from dorsal foregut spheroids was their growth into three-dimensional HEOs with a stratified squamous epithelium expressing regional keratins. Upon extended culture or in vivo transplantation, HEOs significantly increase in maturity, both morphologically and by analysis of later-stage esophageal markers (IVL, CRNN, FLG). Additionally, HEOs could be dissociated, expanded as keratinocytes, and differentiated into stratified squamous epithelium in organotypic raft cultures, demonstrating that HEOs have basal progenitor cells similar to human esophagus (Doupe et al., 2012; Kalabis et al., 2008). In fact, the expression level of differentiation markers in organotypic raft cultures approached that of human esophagus. Generation of fully differentiated and mature cell types from human PSCs has been a challenge across organ systems, and our data suggest that PSC-derived esophageal epithelium is among the most highly differentiated tissues derived to date. 
     HEOs will undoubtedly facilitate studies of human esophageal disease. As one example, Applicant showed how HEOs model human esophageal birth defects. Since SOX2 mutations can cause esophageal atresia in mice and humans, Applicant used HEOs to identify how SOX2 may control human esophageal development since the mechanism underlying its action was unclear (Fantes et al., 2003; Que et al., 2007; Williamson et al., 2006). Applicant first identified transcriptional changes that occur upon loss of SOX2. The current model suggests that the primary role of BMP signaling is to repress Sox2, which represses Nkx2-1; however, Applicant has identified that BMP signaling modulates many transcriptional changes independently of SOX2, suggesting that the current model is oversimplified (Domyan et al., 2011; Rankin et al., 2012) ( FIG. 2B ). Moreover, the data suggests that SOX2 represses canonical Wnt signaling and promotes dorsal endoderm survival. In other contexts, Sox2 can both repress and promote Wnt signaling by a variety of mechanisms including direct binding to TCF/LEF as well as regulating secreted Wnt antagonists (Chen et al., 2008; Kormish et al., 2010; Li et al., 2016; Sinner et al., 2007; Zhou et al., 2016). A role for secreted Wnt antagonists, Sfrp1 and Sfrp2, in tracheoesophageal septation has been shown using Barx1 knockout mice (Woo et al., 2011). In human foregut cultures, SOX2 also regulates transcript levels of SFRP2, and loss of SOX2 causes increased Wnt activity in the dorsal foregut. From this, Applicant concludes that SOX2 restricts the respiratory lineage from the dorsal foregut endoderm, possibly by repressing canonical Wnt signaling. 
     In summary, Applicant has developed a method to generate human PSC-derived HEOs based on temporal manipulation of signals that pattern the early endoderm and foregut. HEO development is strikingly similar to mouse esophageal development and results in a patterned stratified squamous epithelium. Applicant used human foregut cultures and genetic approaches in mice and frogs to identify molecular pathways that are regulated by Sox2 during dorsal-ventral patterning and esophageal specification. Applicant identified that in both humans and mice, SOX2 represses Wnt activity and that failure to do so results in inappropriate dorsal activation of the respiratory program. Thus, HEOs provide a powerful model to study esophageal development and disease. 
     EXPERIMENTAL MODEL AND SUBJECT DETAILS 
     Animals 
     All mice and frogs were housed in the animal facility at Cincinnati Children&#39;s Hospital Medical Center (CCHMC) in accordance with NIH Guidelines for the Care and Use of Laboratory animals Animals were maintained on a 12-hour light-dark cycle with access to water and standard chow ad libitum. Wild-type and mutant mice and  Xenopus laevis  were used for studies on foregut and esophageal embryonic development. The sexes of the embryos were not determined. Male immune deficient NSG (NOD.Cg-Prkdc −scid Il2rg tmlWjI /SzJ) mice, aged 8-16 weeks old, were used for transplantation experiments. Healthy animals were used for all experiments. All experiments were performed under the approval of the Institutional Animal Care and Use Committee of CCHMC (protocols IACUC2016-0004 and IACUC2016-0059). 
     Human ESC/IPSC 
     Human embryonic stem cell (ESC) line H1 (WA01) were purchased from WiCell. Unmodified iPSC lines 65.8, 72.3, and 263.10 were generated and obtained from either the CCHMC Pluripotent Stem Cell Facilities and approved by the institutional review board at CCHMC. CRISPR interference iPSC lines (WTC11 genetic background) were generated and obtained from the Conklin lab at University of California, San Francisco (Mandegar et al., 2016). The H1 line is male, iPSC65.8 line is female, iPSC72.3 line is male, the iPSC263.10 line is male, and the SOX2 CRISPR interference line (CRISPRi-SOX2) is male. All the iPSC lines were checked for and determined to have a normal karyotype, and iPSC65.8 and iPSC72.3 have been tested with an in vivo teratoma assay. 
     Human Biopsy Tissue 
     Human esophageal tissue was collected at time of endoscopy in pediatric patients (all male, ages 3 to 13 years old) that consented to provide esophageal biopsy specimens for research purposes, which is approved by the Institutional Review Board of Cincinnati Children&#39;s Hospital Medical Center (protocol 2008-0090). Samples were used as positive controls for esophageal tissue identity by RNA quantification. 
     Method Details: 
     Experimental Design 
     Pluripotent Stem Cell Lines and Maintenance 
     Both human embryonic and induced pluripotent stem cells (hESCs and hiPSCs) were maintained on feeder-free cultures. Cells are plated on hESC-qualified Matrigel (BD Biosciences, San Jose, Calif.) and maintained at 37° C. with 5% CO 2  with daily replacement of mTeSR1 media (STEMCELL Technologies, Vancouver, Canada); cells were passaged routinely every 4 days using Dispase (STEMCELL Technologies). The H1 HA-tagged SOX2 dox-inducible line was generated by cloning the human SOX2 ORF into pINDUCER20 (Addgene #44012, Meerbrey et al., 2011), generating lentivirus with help of the Viral Vector Core Facility at CCHMC, and transducing hESCs with 2 μL of virus; this line was maintained on selection with mTeSR1 and G418 (500 μg mL-1, ThermoFisher Scientific). 
     Differentiation of Anterior Foregut Cultures and Spheroids 
     Confluent hPSC cultures were treated with Acutase (STEMCELL Technologies) to resuspend as single cells in mTeSR1 and Y-27632 (10 μM, Tocris) and plated on Matrigel. On the following day, differentiation into definitive endoderm was carried out as previously described (McCracken et al., 2014). Briefly, cells were treated with Activin A (100 ng mL-1, R&amp;D systems, Minneapolis, Minn.) and BMP4 (50 ng mL-1, R&amp;D systems) on the first day in RPMI 1640 media (Life Technologies). Cells in the following two days were treated with only Activin A (100 ng mL-1) in RPMI 1640 with increasing concentrations 0.2% and 2% of HyClone defined fetal bovine serum (dFBS, GE Healthcare Life Sciences). 
     For anterior foregut monolayer cultures, cells were treated for 3 days in Noggin (200 ng mL-1) in RPMI 1640 with 2% dFBS, with all-trans retinoic acid (2 μM, Sigma, St. Louis, Mo.) the 3rd day. 
     Alternately, for the generation of anterior foregut spheroids, from definitive endoderm, cells were treated with FGF4 (500 ng mL-1, R&amp;D systems), Noggin (200 ng mL-1) for 3 days in RPMI 1640 with 2% dFBS. Additional factors were tested during this time (described in results), such as CHIR99021 (“chiron” or “chr”, 2 μM, Tocris), Wnt3a (500 ng mL-1, R&amp;D systems), SB431542 (10 μM, Tocris), DEAB (10 μM, Sigma), and retinoic acid (2 μM). 
     Three-Dimensional Culture and Differentiation of Anterior Foregut Spheroids into Human Esophageal Organoids 
     Anterior foregut spheroids were transferred into 50 μL droplets of Matrigel, and are cultured for 3-58 days in the base (“Gut”) media of Advanced DMEM/F12 (ThermoFisher Scientific) supplemented with B27 supplement (1×, ThermoFisher Scientific), N2 supplement (1×, ThermoFisher Scientific), HEPES (13 mM, ThermoFisher Scientific), L-Glutamine (2 mM ThermoFisher Scientific), penicillin/streptomycin (1×, ThermoFisher Scientific), and EGF (100 ng mL −1 , R&amp;D systems). In addition to this base media, the first three days were supplemented with Noggin (200 ng mL −1 ), FGF10 (50 ng mL −1 ), and CultureOne supplement (1×, ThermoFisher Scientific). FGF10 and CultureOne supplementation is continued until the end of the first week in three-dimensional culture. Media was replaced every 3-4 days. For EdU labeling, media was supplemented with EdU (10 μM Invitrogen) for a defined period of time, and was removed by washing with sterile PBS twice before replacing with media without EdU. 
     Keratinocyte and Organotypic Raft Culture 
     Day 41 HEOs were dissociated using TrypLE Select (Gibco) at  37 C for 30-40 minutes, during which they triturated with a 22½ &amp; 27½ gauge needle. After dissociation, cells were reconstituted in complete keratinocyte serum free media (K-SFM, Gibco) supplemented with Y-27632 (10 μM), EGF (10 ng mL −1 ), and penicillin/streptomycin (1×) and subsequently plated onto collagen IV (Sigma) coated plates (1.5 μg cm −2 ) at approximately 1.5×10 4  cells cm −2 . After reaching 90% confluency, HEO-derived keratinocytes were dissociated to single-cells with TrypLE Select and transferred into organotypic rafts cultures. Organotypic rafts were generated as previously described with minor modifications (Hoskins et al., 2009). Briefly, 1.2×10 6  HEO-derived keratinocytes were plated on a 24 mm collagen matrix (rat tail, EMD Millipore) harboring embedded mouse fibroblasts (J2-3T3 cells). Rafts were initially cultured for 4 days with the addition of Y-27632 (10 μM) prior to exposure to the liquid-air interface to generate a stratified epithelium. After 14 days, rafts were fixed in 4% PFA and embedded into paraffin. Sections were stained with H&amp;E and examined for histopathology by routine microscopy. 
     Mouse Models 
     All animal experiments performed were approved by the Institutional Animal Care and Use Committee (IACUC) of Cincinnati Children&#39;s Hospital Medical Center (CCHMC). FoxA2 CreER  mice were obtained from Anne Moon&#39;s lab (Park et al., 2008), Sox2 fl/fl  mice were obtained from Richard Lang&#39;s lab (Shaham et al., 2009), and Sox2 CreER  (stock #017593, Arnold et al., 2011) were obtained from The Jackson Laboratory. Mice were housed at the CCHMC animal facility, and timed matings were used to obtain embryos at the relevant stages. Pregnant dams were gavaged at various stages with tamoxifen at 0.12 mg/g mouse to activate the CreER at appropriate stages. Specifically, pregnant dams in FoxA2 CreER  experiments were gavaged at 6.5 dpc to achieve efficient recombination. In Sox2 CreER  experiments, pregnant dams were gavaged at 8.5 dpc to knockout Sox2 prior to tracheoesophageal separation, and 9.5 dpc to knockout Sox2 during/after tracheoesophageal separation. 
       Xenopus  Experiments 
       Xenopus laevis  adults were purchased from the Nasco (Fort Atkinson, Wis.), and housed according to CCHMC IACUC protocols. Ovulation, in vitro fertilization, and de-jellying of embryos were performed as described (Sive et al., 2000). A mixture of previously validated Sox2 morpholinos (MOs; Van Raay et al., 2005) targeting the 5′UTR (Sox2-UTR MO) and the ATG start codon (Sox2-ATG MO) were injected at the 8-cell stage into each vegetal blastomere (2 ng total MO per blastomere, 8 ng total per embryo) to target endoderm. MOs were synthesized and purchased from GeneTools. Equal amount of control MO was used in control injections. 
     For  Xenopus  explant studies, stage NF20 foregut endoderm tissue was micro-dissected in 1×MBS (Modified Barth&#39;s Saline; Sive et al., 2000)+50 ug/mL gentamycin sulfate (MP Biochemicals), +4% Ficoll-400 (Sigma) and explants were then cultured in 0.5×MBS+0.1% Fatty Acid Free BSA (Fisher)+50 ug/mL gentamycin sulfate with or without the following concentrations of small molecules or recombinant proteins from stages NF25-NF38 (approximately 48 hours): 3.5 μM Bio (Tocris), 50 ng/mL recombinant human BMP4 (R&amp;D systems). 
     In Situ Hybridization 
     In situ hybridization on mouse sections was performed by generating DIG-labeled probes from linearized mouse cDNA plasmids. Probes were allowed to hybridize overnight at 65° C., and on the next day, probes were thoroughly washed before blocking and incubating with anti-DIG alkaline phosphatase antibody (Sigma) in a 1:5,000 dilution in MAB buffer (maleic acid buffer, 100 mM Maleic acid, 150 mM NaCl, pH7.5)+10% heat-inactivated lamb serum (Gibco)+2% blocking reagent (Sigma) overnight at 4° C. Several washes were done before developing the slides using BM purple. In situ hybridization of  Xenopus  explants was performed mostly as described in (Sive et al., 2000). Briefly, embryos and explants were fixed overnight at 40 C in MEMFA (0.1M MOPS, 2 mM EGTA, 1 mM MgSO 4 , 3.7% formaldehyde), dehydrated directly into 100% ethanol, and stored at −20° C. The following minor modifications to the in-situ protocol were used: proteinase K (ThermoFisher) on day 1 was used at 2 ug/mL for 10 minutes on explants; the RNAse A step was omitted on day 2; and finally the anti-DIG-alkaline phosphatase antibody was used at a 1:5,000 dilution in MAB buffer+10% heat-inactivated lamb serum+2% blocking reagent on day 2/3. 
     In situ hybridization on whole-mount  Xenopus  embryos was performed by generating anti-sense DIG labeled nkx2-1 in-situ probe was generated using linearized plasmid full-length nkx2-1 cDNA template (Small et al 2000; Xbal for linearization, T7 to synthesize antisense RNA) with the 10×DIG RNA labeling mix (Sigma) according to manufacturer&#39;s instructions. 
     Immunofluorescence Analysis 
     Tissue cultures were fixed with 4% paraformaldehyde at either room temperature for 15 minutes, 4° C. for 2 hours for cryosectioning, or 4° C. overnight for paraffin embedding/sectioning and mouse embryos. For paraffin embedding and sectioning, following fixation, tissues were dehydrated and embedded into paraffin blocks. Afterwards, paraffin-sectioned slides were deparaffinized and subjected to antigen retrieval in 10 mM sodium citrate for 30 minutes prior to staining. For cryosectioning, tissues were thoroughly washed in PBS, left in 30% sucrose overnight, embedded in OCT compound (VWR), and sectioned at a thickness of 8 μm. Commonly, slides were then permeabilized with 0.5% TritonX-100 in PBS for 10 minutes, blocked in 5% normal donkey serum (Jackson ImmunoResearch) for 1 hour, and incubated in primary antibody overnight at 4° C. On the next day, slides were thoroughly washed in PBS, incubated in secondary antibody (at 1:500) for 1 hour, and then thoroughly washed again. For EdU visualization, Applicant used the Click-iT EdU Alexa Fluor 488 Imaging Kit (Invitrogen) prior to blocking. For wholemount immunofluorescence staining, embryos were placed in 100% methanol immediately after fixation. Embryos were then permeabilized with Dent&#39;s Bleach (4:1:1 MeOH:DMSO:30% H 2 O 2 ) for 2 hours at room temperature, rehydrated with methanol washes, and blocked for several hours at room temperature to overnight at 4° C. Primary antibodies were applied and embryos incubated overnight at 4° C. Then, embryos were thoroughly washed in 0.1% TritonX-100 in PBS before incubating in secondary antibodies overnight at 4° C. Finally, embryos were washed again, dehydrated with methanol washes, and cleared with Murray&#39;s Clear (2:1 benzyl benzoate:benzyl alcohol, Sigma) at least 15 minutes prior to imaging. For a list of antibodies and dilutions used, please see Table 2. 
     RNA Isolation and qPCR 
     Spheroid and organoids were harvested in total, including the embedding matrigel. Collagen plugs from the organotypic raft cultures were first removed from the transwell on day 14, and subsequently harvested in total. Total RNA was isolated using the NucleoSpin RNA kit (Macherey-Nagel) and reverse transcribed to cDNA using the SuperScript VILO cDNA synthesis kit (ThermoFisher Scientific). For qRT-PCR, Applicant used Quantitect SYBR-Green master mix (Qiagen) and ran the reaction on a QuantStudio 6 machine (ThermoFisher Scientific). For a list of primers used, please see Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 List of primers used for qPCR analysis. 
               
               
                 Related to FIG 1-7. 
               
            
           
           
               
               
               
               
            
               
                 Gene 
                 Specie 
                 Strand 
                 Sequence 
               
               
                   
               
               
                 DSG3 
                 human 
                 forward 
                 CGT GGT TGT CTC CGC TAG AA 
               
               
                   
                 human 
                 reverse 
                 CCG AGG TAG CAT TGA GGG TT 
               
               
                   
               
               
                 KRT5 
                 human 
                 forward 
                 CTG GTC CAA CTC CTT CTC CA 
               
               
                   
                 human 
                 reverse 
                 GGA GCT CAT GAA CAC CAA GC 
               
               
                   
               
               
                 FOXE1 
                 human 
                 forward 
                 CGA CAA CCC CAA AAA GTG GC 
               
               
                   
                 human 
                 reverse 
                 GCC CAG TAG TTG CCC TTA CC 
               
               
                   
               
               
                 TBX1 
                 human 
                 forward 
                 GTC TAT GTG GAC CCA CGC AA 
               
               
                   
                 human 
                 reverse 
                 CTG CGT GAT CCG ATG GTT CT 
               
               
                   
               
               
                 SFRP2 
                 human 
                 forward 
                 CCA CCG AGG AAG CTC CAA A 
               
               
                   
                 human 
                 reverse 
                 TTC AGG TCC CTT TCG GAC AC 
               
               
                   
               
               
                 SOX2 
                 human 
                 forward 
                 GCT TAG CCT CGT CGA TGA AC 
               
               
                   
                 human 
                 reverse 
                 AAC CCC AAG ATG CAC AAC TC 
               
               
                   
               
               
                 PAX9 
                 human 
                 forward 
                 GGT AGG GTA AGG AGC CAT GC 
               
               
                   
                 human 
                 reverse 
                 CTG GAG CAG GAA GCC AAG TA 
               
               
                   
               
               
                 GATA4 
                 human 
                 forward 
                 TAG CCC CAC AGT TGA CAC AC 
               
               
                   
                 human 
                 reverse 
                 GTC CTG CAC AGC CTG CC 
               
               
                   
               
               
                 KRT13 
                 human 
                 forward 
                 AGG TGA AGA TCC GTG ACT GG 
               
               
                   
                 human 
                 reverse 
                 GTT GTT TTC AAT GGT GGC G 
               
               
                   
               
               
                 KRT14 
                 human 
                 forward 
                 GGC CTG CTG AGA TCA AAG AC 
               
               
                   
                 human 
                 reverse 
                 TCT GCA GAA GGA CAT TGG C 
               
               
                   
               
               
                 IVL 
                 human 
                 forward 
                 CTG CCT CAG CCT TAC TGT GA 
               
               
                   
                 human 
                 reverse 
                 GGA GGA GGA ACA GTC TTG AGG 
               
               
                   
               
               
                 LEF1 
                 human 
                 forward 
                 CAC TGT AAG TGA TGA GGG GG 
               
               
                   
                 human 
                 reverse 
                 TGG ATC TCT TTC TCC ACC CA 
               
               
                   
               
               
                 TCF1 
                 human 
                 forward 
                 GAC TTG ACC ATC TTC GCC AC 
               
               
                   
                 human 
                 reverse 
                 CCT CAA AGA GCT GGA GAA CCT 
               
               
                   
               
               
                 HNF1B 
                 human 
                 forward 
                 TCA CAG ATA CCA GCA GCA TCA GT 
               
               
                   
                 human 
                 reverse 
                 GGG CAT CAC CAG GCT TGT A 
               
               
                   
               
               
                 PROX1 
                 human 
                 forward 
                 GGC ATT GAA AAA CTC CCG TA 
               
               
                   
                 human 
                 reverse 
                 ACA GGG CTC TGA ACA TGC AC 
               
               
                   
               
               
                 HNF6 
                 human 
                 forward 
                 TGT TGC CTC TAT CCT TCC CA 
               
               
                   
                 human 
                 reverse 
                 GGA GGA TGT GGA AGT GGC T 
               
               
                   
               
               
                 PDX1 
                 human 
                 forward 
                 CGT CCG CTT GTT CTC CTC 
               
               
                   
                 human 
                 reverse 
                 CCT TTC CCA TGG ATG AAG TC 
               
               
                   
               
               
                 (ΔN 
                 human 
                 forward 
                 AGC CAG AAG AAA GGA CAG CA 
               
               
                 isoform) 
                 human 
                 reverse 
                 TCG TGT ACT GTG GCT CAC TAA 
               
               
                 TP63 
                   
                   
                   
               
               
                   
               
               
                 RFX6 
                 human 
                 forward 
                 CCA GTT TTT GAG CTA AGC GAA 
               
               
                   
                 human 
                 reverse 
                 TGG CAT CAA AGA GAG CAG TG 
               
               
                   
               
               
                 MNX1 
                 human 
                 forward 
                 CTG CCT AAG ATG CCC GAC T 
               
               
                   
                 human 
                 reverse 
                 AGC TGC TGG CTG GTG AAG 
               
               
                   
               
               
                 NKX2-1 
                 human 
                 forward 
                 CTC ATG TTC ATG CCG CTC 
               
               
                 (TTF1) 
                 human 
                 reverse 
                 GAC ACC ATG AGG AAC AGC G 
               
               
                   
               
               
                 CDH1 
                 human 
                 forward 
                 GAC CGG TGC AAT CTT CAA A 
               
               
                 (E-CAD) 
                 human 
                 reverse 
                 TTG ACG CCG AGA GCT ACA C 
               
               
                   
               
               
                 AXIN2 
                 human 
                 forward 
                 CTG GTG CAA AGA CAT AGC CA 
               
               
                   
                 human 
                 reverse 
                 AGT GTG AGG TCC ACG GAA AC 
               
               
                   
               
               
                 KRT4 
                 human 
                 forward 
                 CCT GAG ATC CAG AAA GTC CG 
               
               
                   
                 human 
                 reverse 
                 TTC CAT TTG GTC TCC AGG AC 
               
               
                   
               
               
                 CDX2 
                 human 
                 forward 
                 CTG GAG CTG GAG AAG GAG TTT C 
               
               
                   
                 human 
                 reverse 
                 ATT TTA ACC TGC CTC TCA GAG AGC 
               
               
                   
               
               
                 NESTIN 
                 human 
                 forward 
                 GAG GGA AGT CTT GGA GCC AC 
               
               
                   
                 human 
                 reverse 
                 AAG ATG TCC CTC AGC CTG G 
               
               
                   
               
               
                 HOXA1 
                 human 
                 forward 
                 GTA CGG CTA CCT GGG TCA AC 
               
               
                   
                 human 
                 reverse 
                 ACT TGG GTC TCG TTG AGC TG 
               
               
                   
               
               
                 HOXB1 
                 human 
                 forward 
                 AAC CCA CCC AAG ACA GCG AA 
               
               
                   
                 human 
                 reverse 
                 CGC GCT TCT TCT GCT TCA TTC 
               
               
                   
               
               
                 CYP26C1 
                 human 
                 forward 
                 GTT CCC TTC AGT GGC CTA CG 
               
               
                   
                 human 
                 reverse 
                 ACA GCC GAC TCC TTC AGC TC 
               
               
                   
               
               
                 OTX2 
                 human 
                 forward 
                 GGA AGC ACT GTT TGC CAA GAC C 
               
               
                   
                 human 
                 reverse 
                 CTG TTG TTG GCG GCA CTT AGC T 
               
               
                   
               
               
                 CRNN 
                 human 
                 forward 
                 TGT GAT TGT GAA ACC CCA CGA 
               
               
                   
                 human 
                 reverse 
                 GCA CTC TCG CTC AGT GTC TT 
               
               
                   
               
               
                 TMPRSS11A 
                 human 
                 forward 
                 GTC TCC TGG TTC ACT TCC TAG T 
               
               
                   
                 human 
                 reverse 
                 GTG TTG CTT TGT CCG AAA TTG T 
               
               
                   
               
               
                 TMPRSS11D 
                 human 
                 forward 
                 GCA GTC ACC ATA GCT CTA CTT G 
               
               
                   
                 human 
                 reverse 
                 CCA CTC AAA GTC CTG TAT TCC TG 
               
               
                   
               
               
                 CPHA 
                 human 
                 forward 
                 CCC ACC GTG TTC TTC GAC ATT 
               
               
                 (PPIA) 
                 human 
                 reverse 
                 GGA CCC GTA TGC TTT AGG ATG A 
               
               
                   
               
               
                 ID1 
                 human 
                 forward 
                 CTG CTC TAC GAC ATG AAC GG 
               
               
                   
                 human 
                 reverse 
                 GAA GGT CCC TGA TGT AGT CGA T 
               
               
                   
               
               
                 ID3 
                 human 
                 forward 
                 GAG AGG CAC TCA GCT TAG CC 
               
               
                   
                 human 
                 reverse 
                 TCC TTT TGT CGT TGG AGA TGA C 
               
               
                   
               
               
                 HES5 
                 human 
                 forward 
                 GAA AAA CCG ACT GCG GAA GC 
               
               
                   
                 human 
                 reverse 
                 GAC GAA GGC TTT GCT GTG CT 
               
               
                   
               
               
                 FST 
                 human 
                 forward 
                 TGC CAC CTG AGA AAG GCT AC 
               
               
                   
                 human 
                 reverse 
                 TCT TCA CAG GAC TTT GCT TTG ATA C 
               
               
                   
               
               
                 NOG 
                 human 
                 forward 
                 TGG TGG ACC TCA TCG AAC AC 
               
               
                   
                 human 
                 reverse 
                 ATG AAG CCT GGG TCG TAG TG 
               
               
                   
               
               
                 CCL26 
                 human 
                 forward 
                 AAC TCC GAA ACA ATT GTG ACT CAG CTG 
               
               
                   
                 human 
                 reverse 
                 GTA ACT CTG GGA GGA AAC ACC CTC TCC 
               
               
                   
               
               
                 CDH26 
                 human 
                 forward 
                 TGC TTT TTC TGT TGC GAT GCT 
               
               
                   
                 human 
                 reverse 
                 CTT GCC ATA ACC CCA GCT C 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 List of antibodies used for immunofluorescence staining. 
               
               
                 Related to FIGS 1-7. 
               
            
           
           
               
               
               
               
               
            
               
                 Antibody 
                 Company 
                 Catalog 
                 RRID Number 
                 Dilutio 
               
               
                   
               
               
                 Goat anti-Sox2 
                 Santa Cruz Biotechnology 
                 #sc-17320  
                 RRID:AB_2286684 
                 1:250 
               
               
                   
                   
                 (Y-17) 
                   
                   
               
               
                 rabbit anti-Sox2 
                 Abcam 
                 #ab97959 
                 RRID:AB_2341193 
                 1:1000 
               
               
                 rabbit anti-p63 
                 Santa Cruz Biotechnology 
                 #sc-8343 
                 RRID:AB_653763 
                 1:200 
               
               
                 mouse anti-HNF1b 
                 BD Transduction 
                 #612504 
                 RRID:AB_399805 
                 1:500 
               
               
                   
                 Laboratories 
                   
                   
                   
               
               
                 rat anti-E-cadherin 
                 R&amp;D Systems 
                 #MAB7481 
                 RRID:AB_2076679 
                 1:1000 
               
               
                 goat anti-E-cadherin 
                 R&amp;D Systems 
                 #AF648 
                 RRID:AB_355504 
                 1:1000 
               
               
                 mouse anti-E- 
                 BD Transduction 
                 #610182 
                 RRID:AB_397581 
                 1:500 
               
               
                 cadherin 
                 Laboratories 
                   
                   
                   
               
               
                 rabbit anti-Nkx2.1 
                 Abcam 
                 #ab76013 
                 RRID:AB_1310784 
                 1:1000 
               
               
                 rat anti-Krt8 
                 DSHB 
                 #TROMA-I-S 
                 RRID:AB_531826 
                 1:100 
               
               
                 mouse anti-Krt4 
                 Abcam 
                 #ab9004 
                 RRID:AB_306932 
                 1:200 
               
               
                 rabbit anti-Krt13 
                 Abcam 
                 #ab92551 
                 RRID:AB_2134681 
                 1:1000 
               
               
                 rabbit anti-Krt14 
                 BioLegend 
                 #905301  
                 RRID:AB_2565048 
                 1:2000 
               
               
                   
                   
                 (PRB-155P) 
                   
                   
               
               
                 rabbit anti-Ki67 
                 Cell Marque 
                 #275R-15 
                 RRID:AB_1158037 
                 1:100 
               
               
                   
                   
                 (SP6) 
                   
                   
               
               
                 rabbit anti-Ivl 
                 Atlas Antibodies 
                 #HPA055211 
                 RRID:AB_2682739 
                 1:250 
               
               
                 rabbit anti-Dsg3 
                 Cell Marque 
                 #436R-15 
                   
                 1:200 
               
               
                 goat anti-FoxA2 
                 Santa Cruz Biotechnology 
                 #sc-6554 
                 RRID:AB_2262810 
                 1:500 
               
               
                 rat anti-HA-Biotin 
                 Sigma-Aldrich (Roche) 
                 #12158167001 
                 RRID:AB_390915 
                 1:300 
               
               
                   
                   
                 (3F10) 
                   
                   
               
               
                 goat anti-Pdx1 
                 Abcam 
                 #ab47383 
                 RRID:AB_2162359 
                 1:5000 
               
               
                 goat anti-Gata4 
                 Santa Cruz Biotechnology 
                 #sc-1237 
                 RRID:AB_2108747 
                 1:200 
               
               
                 rabbit anti-Caspase 3 
                 Cell Signaling 
                 #9661 
                 RRID:AB_2341188 
                 1:200 
               
               
                 (cleaved) 
                   
                   
                   
                   
               
               
                 rabbit anti-Cdx2 
                 Cell Marque 
                 #235R-15 
                 RRID:AB_1516799 
                 1:200 
               
               
                   
                   
                 (EPR2764Y) 
                   
                   
               
               
                 mouse anti-Cdx2 
                 BioGenex 
                 #cdx2-88 
                 RRID:AB_2650531 
                 1:300 
               
               
                 rabbit anti-B-catenin 
                 Santa Cruz 
                 #sc-7199 
                 RRID:AB_634603 
                 1:100 
               
               
                 mouse anti-Filaggrin  
                 Santa Cruz 
                 #sc-66192 
                 RRID:AB_1122916 
                 1:200 
               
               
                 goat anti-Cornulin 
                 R&amp;D Systems 
                 #AF3607 
                 RRID:AB_2085498 
                 1:200 
               
               
                 anti-DIG alkaline 
                 Sigma-Aldrich 
                 #11093274910 
                 RRID:AB_514497 
                 1:5000 
               
               
                 phosphatase 
                   
                   
                   
                   
               
               
                 AlexaFluor Donkey 
                 Thermo Fisher Scientific 
                 #A11055 
                 RRID:AB_2534102 
                 1:500 
               
               
                 anti-goat 488 
                   
                   
                   
                   
               
               
                 AlexaFluor Donkey 
                 Thermo Fisher Scientific 
                 #A11057 
                 RRID:AB_2534104 
                 1:500 
               
               
                 anti-goat 568 
                   
                   
                   
                   
               
               
                 AffiniPure Donkey 
                 Jackson ImmunoResearch 
                 #715-605-150 
                 RRID:AB_2340862 
                 1:500 
               
               
                 anti-mouse 647 
                 laboratories 
                   
                   
                   
               
               
                 AlexaFluor Donkey 
                 Thermo Fisher Scientific 
                 #A10037 
                 RRID:AB_2534013 
                 1:500 
               
               
                 anti-mouse 568 
                   
                   
                   
                   
               
               
                 AlexaFluor Donkey 
                 Thermo Fisher Scientific 
                 #A31573 
                 RRID:AB_2536183 
                 1:500 
               
               
                 anti-rabbit 647 
                   
                   
                   
                   
               
               
                 AlexaFluor Donkey 
                 Thermo Fisher Scientific 
                 #A10040 
                 RRID:AB_2534016 
                 1:500 
               
               
                 anti-rabbit 546 
                   
                   
                   
                   
               
               
                 AffiniPure Donkey 
                 Jackson ImmunoResearch 
                 #712-605-153 
                 RRID:AB_2340694 
                 1:500 
               
               
                 Anti-Rat 647 IgG 
                 laboratories 
                   
                   
                   
               
               
                 Mouse anti-CDH17 
                 R&amp;D Systems 
                 #MAB1032 
                 — 
                 1:200 
               
               
                 Rabbit anti-CLDN18 
                 Atlas Antibodies 
                 #HPA018446 
                 — 
                 1:100 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 Resources Table 
               
               
                   
               
             
            
               
                 Bacterial and Virus Stains 
               
               
                 Biological Samples 
               
            
           
           
               
               
               
            
               
                 Human Esophageal Biopsies 
                 Rothenberg Lab 
                 CB2096, CB2394, 
               
               
                   
                 CCHMC 
                 CB3027, CB3082, 
               
               
                   
                   
                 and CB3103 
               
            
           
           
               
            
               
                 Chemicals, Peptides, and Recombinant Proteins 
               
            
           
           
               
               
               
            
               
                 recombinant human FGF4 
                 R&amp;D Systems 
                 Cat#235-F4 
               
               
                 recombinant human EGF 
                 R&amp;D Systems 
                 Cat#236-EGF 
               
               
                 recombinant human Noggin 
                 R&amp;D Systems 
                 Cat#6057-NG 
               
               
                 recombinant human BMP4 
                 R&amp;D Systems 
                 Cat#314-BP 
               
               
                 recombinant human FGF10 
                 R&amp;D Systems 
                 Cat#345-FG 
               
               
                 recombinant human Wnt3a 
                 R&amp;D Systems 
                 Cat#5036-WN 
               
               
                 Activin A 
                 Cell Guidance 
                 Cat#GFH6 
               
               
                   
                 Systems 
                   
               
               
                 CHIR99021 
                 Stemgent 
                 Cat#04-0004 
               
               
                 BIO 
                 Tocris 
                 Cat#3194 
               
               
                 Y-27632 dihydrchloride 
                 Tocris 
                 Cat#1254 
               
               
                 SB431542 
                 Tocris 
                 Cat#1614 
               
               
                 Doxycycline 
                 Sigma-Aldrich 
                 Cat#3447 
               
               
                 Tamoxifen 
                 Sigma-Aldrich 
                 Cat#T5648 
               
               
                 hESC-qualified Matrigel 
                 BD Biosciences 
                 Cat#354277 
               
               
                 mTeSR1 media 
                 Stem Cell 
                 Cat#5850 
               
               
                   
                 Technologies 
                   
               
               
                 Advanced DMEM:F12 
                 Thermo Fisher 
                 Cat#12634-010 
               
               
                   
                 Scientific 
                   
               
               
                 Matrigel 
                 BD Biosciences 
                 Cat#354234 
               
               
                 Defined fetal bovine serum dFBS) 
                 Hyclone 
                 Cat#SH30070.02 
               
               
                 Proteinase K 
                 Thermo Fisher 
                 Cat#AM2548 
               
               
                   
                 Scientific 
                   
               
               
                 Normal donkey serum 
                 Jackson Immuno- 
                 Cat#017-000-121 
               
               
                   
                 research Labs 
                   
               
               
                 Heat-inactivated lamb serum 
                 Gibco 
                 Cat#16070096 
               
               
                 Blocking Reagent 
                 Sigma-Aldrith 
                 Cat#11096176001 
               
               
                 L-glutamine 
                 Thermo Fisher 
                 Cat#25030-081 
               
               
                   
                 Scientific 
                   
               
               
                 Pen/Strep (100x) 
                 Thermo Fisher 
                 Cat#15140-122 
               
               
                   
                 Scientific 
                   
               
               
                 50x B27 supplement w/o Vitamin A 
                 Thermo Fisher 
                 Ca#12587-010 
               
               
                   
                 Scientific 
                   
               
               
                 Non-essential Amino Acids (100x) 
                 Thermo Fisher 
                 Cat#11140050 
               
               
                   
                 Scientific 
                   
               
               
                 HEPES Buffer 
                 Thermo Fisher 
                 Cat#15630080 
               
               
                   
                 Scientific 
                   
               
               
                 N2 Supplement 
                 Thermo Fisher 
                 Cat#17502-048 
               
               
                   
                 Scientific 
                   
               
               
                 Dispase 
                 Thermo Fisher 
                 Cat#17105-o41 
               
               
                   
                 Scientific 
                   
               
               
                 Acutase 
                 Thermo Fisher 
                 Cat#A11105-01 
               
               
                   
                 Scientific 
                   
               
               
                 Collagen Type I, rat tail 
                 EMD Millipore 
                 Cat#08-115 
               
               
                 Transwell 24 mm Polyester Membrane  
                 Corning 
                 Cat#3450 
               
               
                 Inserts, 6 well plate 
                   
                   
               
               
                 Deep Well Plate, 6 well 
                 BD 
                 Cat#355467 
               
               
                 Ahlstrom Filter Papers—Grade 222 
                 Fisher Scientific 
                 Cat#09-790-49J 
               
               
                 1,2-Dioctanoyl-sn-glycerol 
                 Cayman Chemicals 
                 Cat#62225 
               
               
                 F12 Media 
                 Invitrogen 
                 Cat#11755-054 
               
               
                 1x DMEM 
                 Invitrogen 
                 Cat#11965-084 
               
               
                 Fetal Bovine Serum (FBS) 
                 HyClone 
                 Cat#SH30071.03 
               
               
                 Adenine 
                 Sigma-Aldrich 
                 Cal#A2786-5G 
               
               
                 Cholera toxin 
                 EMD Millipore 
                 Cat#227035 
               
               
                 Hydrocortisone 
                 Sigma-Aldrich 
                 Cat#H0888-1G 
               
               
                 Fungizone (Amphotericin B) 
                 Omega Scientific 
                 Cat#FG-70 
               
               
                 Insulin, human recombinant 
                 Invitrogen 
                 Cat#12585-014 
               
               
                 EGF 
                 Sigma-Aldrich 
                 Cat#1257-0.1MG 
               
               
                 RNAlater 
                 Thermo Fisher 
                 Cat#AM7020 
               
               
                   
                 Scientific 
                   
               
            
           
           
               
            
               
                 Critical Commercial Assays 
               
            
           
           
               
               
               
            
               
                 Quantitect SYBR Green 
                 Qiagen 
                 Cat#204145 
               
               
                 Nucleospin RNA 
                 Macherey-Nagel 
                 Cat#740955 
               
               
                 SuperScript VILO cDNA synthesis kit 
                 Thermo Fisher 
                 Cal#11754250 
               
               
                   
                 Scientific 
                   
               
               
                 Click-iT EdU Alexa Fluor 488 Imaging Kit 
                 Invitrogen 
                 Cat#C10337 
               
            
           
           
               
            
               
                 Experimental Models: Cell Lines 
               
            
           
           
               
               
               
            
               
                 Human: H1 ES cells (passage 42) 
                 CCHMC Pluripotent 
                 NIH hESC-10-0043 
               
               
                   
                 Stem cell core/WiCell  
                   
               
               
                   
                 Research Institute 
                   
               
               
                 Human: H9 ES cells (passage 30) 
                 CCHMC Pluripotent 
                 NIH hESC-10-0062 
               
               
                   
                 Stem cell core/WiCell  
                   
               
               
                   
                 Research Institute 
                   
               
               
                 Human: iPS65.8 iPS cells (passage 44) 
                 CCHMC Pluripotent 
                   
               
               
                   
                 Stem cell core 
                   
               
               
                 Human: iPS72.3 iS cells (passage 35) 
                 CCHMC Pluripotent 
                   
               
               
                   
                 Stem cell core 
                   
               
               
                 Human: iPS263.10 iPS  
                 cells (passage 30) 
                   
               
               
                 Human: WTC: CRISPRi-SOX2 iPS  
                 Conklin lab 
                 Mandegar et al. 
               
               
                 cells (passage 43) 
                   
                 2016 
               
            
           
           
               
            
               
                 Experimental Models: Organisms/Strains 
               
            
           
           
               
               
               
            
               
                 Mouse: Foxa2tm2.1(cre/Esr1*)Moon/J 
                 The Jackson 
                 JAX: 008494 
               
               
                   
                 Laboratory 
                   
               
               
                 Mouse: B6.:129S-Sox2trm1(cre/ERT2)Hoch/J 
                 The Jackson 
                 JAX: 017593 
               
               
                   
                 Laboratory 
                   
               
               
                 Mouse: Sox2tm1.1Lan/J 
                 Lang Lab 
                 JAX: 013093) 
               
               
                 
                   Xenopus laevis 
                 
                   
                   
               
            
           
           
               
            
               
                 Oligonucleotides 
               
            
           
           
               
               
               
            
               
                 sox2- UTR MO: CTGGCAGAGCGGAATCAGTTTCCCA 
                 GeneTools 
                 N/A (synthesized) 
               
               
                 sox2- ATO MO: AGCTCGGTCTCCATCATGCTGTAC 
                 GeneTools 
                 N/A (synthesized) 
               
               
                 control MO: CCTOTTACCTCAGTTALAATTTATA 
                 GeneTools 
                 N/A (synthesized) 
               
               
                 See Table S1 for qRT-PCR primers. 
                 IDT DNA 
                 N/A (synthesized) 
               
            
           
           
               
            
               
                 Recombinant DNA 
               
            
           
           
               
               
               
            
               
                 pINDUCER20 
                 Ciccia et al._ 2011 
                 Addgene plasmid 
               
               
                   
                   
                 44012 
               
            
           
           
               
            
               
                 Software and Algorithms 
               
            
           
           
               
               
               
            
               
                 Imans 
                 While 
                 N/A 
               
               
                 NIS Elements 
                 Nikon 
                 N/A 
               
               
                 Computational Suite for Bioinformaticians and Biologists 
                   
                 https://sourceforge. 
               
               
                 version 2.1 (CSBB v2.1) 
                   
                 net/projects/csbb- 
               
               
                   
                   
                 v2-1/ 
               
               
                 Gene Set Enrichment Analysis (GSEA) 
                   
                 Subramanian et al, 
               
               
                   
                   
                 2005 
               
               
                 PRISMv9 graphing and statistical software 
                 GraphPad Software 
                 N/A 
               
               
                   
               
            
           
         
       
     
     RNA Sequencing and Analysis 
     Whole-transcriptome RNA sequencing of anterior foregut cultures and HEOs (n=3 per condition or time point) was performed by the DNA sequencing and Genotyping Core Facility on an Illumina Hi-Seq 2500 platform from a Poly(A) and TruSeq library generated from isolated total RNA. RNA sequencing parameters were 75 bp single-end sequencing at a depth of 10M reads per samples. Fastq read files for each sample were obtained and then aligned using the Computational Suite for Bioinformaticians and Biologists version 2.1 (CSBB-v2.1, https://sourceforge.net/projects/csbb-v2-1/). Raw transcript counts and normalized transcripts per million (TPM) values were obtained and analyzed for differential expression with CSBB-v2.1 and for Gene Set Enrichment Analysis (GSEA, Subramanian et al., 2005). For differential expression, statistical and biological significance was set at P&lt;0.05, FDR&lt;0.05, log fold-change&gt;1, with a minimum of 3 transcript counts in 3 of the 6 samples. For heatmap visualization and hierarchical clustering analysis, Morpheus (https://software.broadinstitute.org/morpheus/) was used. 
     Anterior foregut transcriptome analyses were cross-referenced with SOX2 and SMAD1 ChIP-seq peaks from GEO sets (GSE61475, Tsankov et al., 2015; GSE47058, Watanabe et al., 2014) using HOMER to obtain lists of genes whose expression is potentially regulated by these transcription factors. Peak cutoff distance was set at 50 kb from the transcription start site of any particular gene. 
     HEO analyses were compared to previously published RNA-seq samples on in vitro generated organoids (intestine and gastric), EPC2 cultures, and biopsies from the ENCODE Roadmap project, which including the following tissues: skin, esophagus, small intestine, stomach, colon, and lung. To compare in-house data with public data, Applicant used Upper Quantile [between-Lane Normalization] from EDASEQ [http://bioconductor.org/packages/release/bioc/vignettes/EDASeq/inst/doc/EDASeq.pdf]. Applicant used to CSBB&#39;s [Computational Suite for Bioinformaticians and Biologists] version 3.0 [https://github.com/csbbcompbio/CSBB-v3.0] UpperQuantile module. Applicant generated a matrix of expression of genes across in-house and public samples and quantile-normalized using CSBB-v3.0&#39;s UpperQuantile module. Then, Applicant log 2 transformed the quantile normalized matrix in R. Log 2 
     Transformed Matrix was Used for all Downstream Analysis. 
     Applicant also used SVA [https://bioconductor.org/packages/release/bioc/vignettes/sva/inst/doc/sva.pdf] on the log 2 transformed—quantile normalized matrix to check if there are any latent variables/surrogate variables to correct. Applicant found no surrogate variables to correct for. This approach gave Applicant confidence that Upper-Quantile normalization followed by Log 2 transform is robust enough to remove batch and sequencing effects from the data. 
     Quantification and Statistical Analysis 
     For experiments involving spheroid patterning, organoid outgrowth, and raft experiments, “n” represents the number of replicates performed in each experiment (1 well of 3-7 organoids or 30-50 spheroids were collected for each replicate in matrigel culture, all samples from 1 well of an organotypic raft culture are considered a single replicate). For animal experiments, “n” represents the number of embryos analyzed. All data quantification is represented as the mean±SD. To compare the various conditions tested in spheroid patterning and organoid outgrowth, t-tests with 2-tailed distribution not assuming equal (i.e. un-equal) variance was used in Microsoft Excel, where *p≤0.05, **p≤0.01, ***p≤0.001, and ****p≤0.0001. 
     Details for quantification and statistical analysis for  FIGS. 1-7   
       FIG. 1 : For  1 H, a minimum of 20 spheroids from two experiments were assessed. For all qPCR results, the data is representative of a minimum of 2 separate experiments with n=3 wells (50-100 spheroids in each well) for each experiment. RA experiments were replicated in both H1 and iPS263.10 cell lines. 
       FIG. 2 : The data is representative of 2 separate experiments with n=3 wells (averaging 30-50 spheroids per well) in each experiment utilizing the H1 hESC line. 
       FIG. 3 : Generation of organoids is representative of 40+ experiments across 4 hES and iPS cell lines: H1, iPS 65.8, iPS 72.3, iPS 263.10. The qPCR data is representative of 2 separate experiments with n=3 wells (3-12 organoids per well) and were compared to n=5 patient biopsy samples. 
       FIG. 4 : n=2-4 wells for the HEOs to organotypic raft culture experiment. n=6-10 organoids at each time-point for the EdU experiment. n=5 patient esophageal biopsy samples. Experiments were done in the H1 hESC line. 
       FIG. 5 : For Sox2-DE-LOF embryos, n=3 embryos of each genotype at E9.5, and n=2 embryos for each analysis type for each genotype at E11.5. For Sox2 driven Sox2 cKO embryos, n=3 embryos analyzed for IF of each stage of tamoxifen administration and corresponding stage harvest. 
       FIG. 6 : All data from the human PSC-derived cultures are representative of 3 separate experiments with n=3 wells for each condition per experiment. 
     Data and Software Availability 
     The accession number for the data generated is Gene Expression Omnibus (GEO): GSE112886. This includes the organoid outgrowth comparison (1 versus 2-month human esophageal organoids,  FIG. 3 ) as well as the SOX2-knockdown experiment in dorsal and ventral anterior foregut cultures ( FIG. 7  and  FIG. 14A-14D ). 
     ChIP-seq data of SOX2 and SMAD1 ChIP-seq peaks were downloaded from the public database GEO with accession numbers GSE61475 (Tsankov et al., 2015) and GSE47058 (Watanabe et al., 2014), respectively. RNA-seq data of biopsies and EPC2 cultures were downloaded from the public database GEO. The accession numbers for the samples are: GSM1120313 and GSM1120314 (small intestine), GSM1010946 and GSM1120308 (lung), GSM1120307 and GSM11010960 (stomach), GSM1120315 and GSM1010974 (large intestine), GSM1010956 and GSM1120303 (esophagus), GSM2343841 and GSM234564 (lower leg skin), and GSM1592609-GSM1592611 (EPC2 day 0 cultures). The complete RNA-seq processing pipeline was done using Computational Suite for Bioinformaticians and Biologists version 2.1 (CSBB-v2.1) and is available at https://sourceforge.net/projects/csbb-v2-1/. 
     Disease States 
     With the advent of the human esophageal organoid models described herein, Applicant sought to apply this system to study various diseases that affect the esophagus. Applicant examined the role of Sox2 in the patterning and separation of the anterior foregut and formation of the esophagus. Though esophageal atresia is mainly focused on the proper resolution of the esophageal and respiratory tracts, its sequalae in human patients go far beyond this primary issue. This is because the treatment for esophageal atresia is surgery to fix the anatomical defect; however, the underlying mechanisms that led to the primary defect and how they may compromise the proper development of the esophagus (and respiratory tract) are not addressed. Among the many genes that are associated with esophageal atresia, the role of two genes, Sox2 and a Fanconi anemia gene (FANCA), in esophageal development, are discussed herein. 
     Previous studies have examined the role of Sox2 in esophageal development and homeostasis. In the Sox2 hypomorphic embryos, the esophagus of mutant embryos where foregut separation occurred had altered properties, including lack of expression of stratified squamous epithelial markers p63 and Krt14, as well as expression of gastric and intestinal markers (Que et al., 2007). However, interpreting these results in terms of Sox2&#39;s role in early versus later esophageal development is challenging to decipher, as these changes could be a result of early mispatterning in the mutant foregut as opposed to a continued requirement for Sox2 to drive esophageal growth and maturation. Studies in the adult esophagus do suggest that Sox2 continues to play a role past the developmental stage. Sox2 expressing cells in the esophagus are critical for maintaining homeostasis, and when ablated, this leads to the complete loss of the basal layers and atypical cells residing in the esophagus (Arnold et al., 2011). Aside from just serving as a marker of basal cells in the adult esophagus, Sox2 overexpression in the esophagus results in expansion of the basal compartment and decreased differentiation of the suprabasal layers (Liu et al., 2013). Apart from the esophagus, Sox2 plays a homeostatic role in other endodermal organs. In the trachea, loss of Sox2 postnatally leads to less proliferation and a decreased proportion of basal (less p63+), ciliated, and Clara cells (Que et al., 2009). However, in the adult stomach, it appears that Sox2 is dispensable for homeostasis of the tissue, though it may have tumor suppressive roles (Sarkar et al., 2016). Despite this, the role of Sox2 in the developing esophagus (post-foregut-separation) has yet to be carefully examined, which may yield insights into the other issues of patients with esophageal atresia. 
     Fanconi anemia is recessive disorder (for any particular FANC complementation group gene) and is also associated with esophageal atresia, among other GI defects, though these GI issues occur in only a subset of patients (i.e. low penetrance) (Fausett and Klingensmith, 2012). Some patients do not have major congenital defects, though many patients have defects, which span across multiple organ systems. In various patients, in addition to the hematological issues, the presenting defects have similarities with the VACTERL association of symptoms, which consist of vertebral, anal, cardiac, trachea-esophageal, renal, and limb defects (Auerbach, 2009). Of all the FANC complementation group genes that cause Fanconi anemia, the most common are FANCA, FANCC, and FANCG (Auerbach, 2009; Nebert et al., 2016). There is a thought that the Shh signaling pathway may be involved in Fanconi anemia, based on the similarity of symptoms in Shh mutants and Fanconi anemia (Lubinsky, 2015). However, virtually nothing is known about how esophageal atresia develops in some cases of Fanconi anemia. An obstacle to understanding how esophageal atresia develops in Fanconi anemia patients is that mouse models of Fanconi anemia do not recapitulate most of the developmental abnormalities (Bakker et al., 2013). Thus, using human organoid models of development may provide a breakthrough in understanding the pathogenesis of various GI malformations in Fanconi anemia. 
     In addition to the congenital disease esophageal atresia, Applicant are also interested in the later diseases affecting the esophagus, such as Barrett&#39;s esophagus. Barrett&#39;s esophagus (or Barrett&#39;s metaplasia) is a condition where the stratified squamous epithelium of the esophagus transforms into a columnar (intestinal-like) epithelium, which predisposes the patient towards esophageal adenocarcinoma (De Jonge et al., 2014). The mechanism underlying this transformation is actively being studied, and there are multiple hypotheses concerning the cell-of-origin of this ectopic columnar epithelium. Of these, the more likely models include transformation of esophageal cells into intestinal-like cells, transformation of the transitional epithelium at the gastroesophageal junction, and transformation of submucosal glands (Jiang et al., 2017; Leedham et al., 2008; Wang et al., 2010). 
     Previous studies testing this hypothesis have found that acid and bile salts upregulate Cdx1 and Cdx2 in cultured esophageal cells, potentially by regulating the Cdx2 promoter (Huo et al., 2010; Kazumori et al., 2006, 2009; Liu et al., 2007). Additionally, in culture, acid and bile salts lead to downregulation of stratified squamous epithelial genes (Ghatak et al., 2013). However, Cdx2 induction alone does not appear to be able to fully transform esophageal cells, though it can result in mild downregulation of some stratified squamous epithelial genes, upregulate some intestinal genes (Muc2, Villin), and mildly alters the epithelial morphology (Kong et al., 2011; Liu et al., 2007). BMP activation, alone or in combination with Cdx2, appears to have a stronger effect to downregulate stratified squamous epithelial genes in the mouse esophagus and cultured human esophageal cells, though these alterations are still far from the full transformation into a columnar epithelium, by morphology or gene expression (Mari et al., 2014). Other signaling pathways, such as Wnt and Notch, may be altered in esophageal cells exposed to bile acids (Chen et al., 2012). Notch inhibition leads to some changes in cultured esophageal cells, including downregulation of stratified squamous epithelial genes, upregulation of columnar epithelial genes, and increased intercellular spaces in the basal compartment (Kasagi et al., 2018; Vega et al., 2014). However, from these studies, it is unclear which signaling pathways contribute to the pathogenesis of Barrett&#39;s metaplasia as opposed to simply being changed as a result of all the other morphological changes. Accordingly, HEOs may allow rapid combinatorial screening of these suspected signaling pathways in a more biologically relevant model. 
     Another disease affecting the pediatric and adult esophagus is eosinophilic esophagitis, which is a chronic immune-mediated disease that causes difficulty feeding or food impaction, vomiting, and abdominal pain. The diseased esophagus undergoes some changes, including esophageal strictures from fibrosis and muscle wall thickening, basal cell hyperplasia and dilated intercellular spaces in the epithelium, and the hallmark finding of high levels of eosinophils in the esophageal epithelium (Furuta and Katzka, 2015). It is classically thought that an impaired barrier and exposure to certain antigens initiate and then maintain the disease, as the inflamed esophagus recruits immune cells and further maintains the impaired barrier (Caldwell et al., 2017; Furuta and Katzka, 2015). 
     The recruited type 2 helper T-cells (and other immune cells) secrete multiple cytokines, which cause broad changes in the esophageal epithelium and surrounding layers. In the epithelium, IL-13 upregulates eotaxin-3 (or CCL26), a chemokine that attracts eosinophils. In addition to CCL26 and other target inflammatory genes, IL-13 exposure results in basal cell hyperplasia in the mouse esophagus, and downregulation of differentiated stratified squamous epithelial markers (such as FLG, IVL, SPRR family of proteins) (Blanchard et al., 2010; Jiang et al., 2015; K C et al., 2015; Rochman et al., 2017). Air-liquid interface cultures of esophageal keratinocytes treated with IL-13 also display decreased transepithelial electrical resistance (TEER), demonstrating barrier dysfunction (D&#39;Mello et al., 2016; Davis et al., 2016; Wu et al., 2018). 
     Results 
     The Role of Sox2 in Later Esophageal Development 
     To examine the role of Sox2 in the development and maturation of the esophagus (post-separation of the esophagus from the respiratory tract), Applicant utilized the same mouse model as with the previous chapter to conditionally knockout Sox2 in Sox2 expressing cells. Applicant mated female Sox2 fl/f  mice to male Sox2 CreERT2/+  mice and either the dams were gavaged with tamoxifen at E11.5 and E14.5 or the pups at P1 were injected with tamoxifen, which were then harvested several days post-gavage to examine the effects of Sox2 loss in the esophagus at various developmental stages ( FIG. 1A ). Earlier loss of Sox2 (gavage at E11.5) results in delayed stratification at E14.5, as evident by the mostly simple columnar epithelium in the esophagus of the conditional knockout compared to the wild-type, which has stratified to 2 layers at this stage ( FIG. 1B ). Later knockout of Sox2 (E14.5 gavage) results in a somewhat smaller esophagus, though stratification appears normal. Finally, early postnatal knockout of Sox2 (P1) appears to have no gross changes to the esophagus ( FIG. 1B ). In these embryos where Sox2 was knocked-out after separation of the anterior foregut, there was no immediate re-expression of Nkx2-1 in the esophagus, though the E11.5 gavaged embryos had a few cells in the esophagus expressing Nkx2-1 at E17.5 ( FIG. 1B,1E ) 
     Because the most obvious changes occurred only in the E11.5 gavaged embryos, Applicant looked more carefully at these esophagi at E17.5 for various patterning and differentiation markers. Grossly, the esophageal epithelium appeared less folded (upon itself) and had a larger average luminal diameter. Besides the confirmatory loss of Sox2, the basal layer of the Sox2 knockout esophagus appears normal—it expresses p63 and Krt14 and lacks Krt8 expression ( FIG. 1C ). However, the suprabasal layer is obviously altered: Krt13 is absent while Krt8 is robustly expressed; there are proliferating (Ki67+) positive cells, which is not present in the wild-type esophagus; and, the epithelial morphology persists as a columnar epithelium ( FIG. 1C-D ). However, Applicant did not find evidence of Muc2 or Muc5ac production, though further future analysis (such as Alcian blue staining) may reveal mucous generation (data not shown). Aside from the few cells that express Nkx2-1 in the Sox2 knocked-out esophagus, other key intestinal and gastric markers were not expressed in either wild-type of Sox2 knockout esophagi ( FIG. 1E ). In addition to the critical role Sox2 plays in early patterning, these data directly demonstrate the necessity of Sox2 for proper esophageal development and maturation after the separation of the esophagus from the respiratory tract. 
     Fanconi&#39;s Anemia and Early Esophageal Development 
     In addition to Sox2, various other genes are associated with esophageal atresia, and the mechanisms that underlie foregut defects resulting from mutations in some of these genes are unknown. Loss of a Fanconi anemia complementation group gene can result in multiple issues with variable penetrance, including GI issues like atresias (esophageal, duodenal, anal), CNS defects, renal defects, and growth abnormalities (Auerbach, 2009; De Jong et al., 2010). To begin to understand how these genes result in esophageal atresia, Applicant sought to model the effects of a FANCA deficiency in esophageal development using HEOs. 
     Applicant used an iPSC line generated from a patient lacking FANCA that can be maintained/rescued using a dox-inducible FANCA construct. This line could successfully generate HEOs using described herein with or without doxycycline treatment ( FIG. 2A ). Foregut patterning did not appear to be altered in the low or absent expression of FANCA ( FIG. 2B ). Upon outgrowth (2-4 weeks) of the dorsal anterior foregut spheroids into HEOs, the FANCA-deficient organoids appear to consistently be smaller than the “control”/rescued (+dox) organoids ( FIG. 2C, 2F ). However, FANCA-deficient HEOs have increased numbers of KI67+ cells compared to control HEOs at 1 month ( FIG. 2D, 2G ). There appears to be no difference in cell death (by cleaved Caspase 3 staining) in either condition (data not shown). Additionally, Applicant did not find a significant difference in the expression of stratified squamous epithelial markers between the two conditions (data not shown). To confirm that organoids responded to doxycycline treatment and expressed FANCA, Applicant probed for FANCA and response of FANCD2 to hydroxyurea treatment when FANCA is present. Western blotting clearly revealed knockout and rescue of FANCA without or with doxycycline treatment, respectively, and a shift in FANCD2 protein size upon doxycycline and hydroxyurea treatment ( FIG. 2E ). 
     Modeling Barrett&#39;s Esophagus Using HEOs 
     In addition to studying early defects in foregut and esophageal development, Applicant also wanted to apply HEOs to model later diseases affecting the esophagus, such as Barrett&#39;s metaplasia. There has been a lot of work trying to identify the cell-of-origin and to understand the mechanisms that result in the transformation of the stratified squamous epithelium into an intestinal (columnar) epithelium. However, because of the challenges in accurately modeling the human pathological process in mice, it is believed that using an HEO model can serve as a complementary approach to understanding how Barrett&#39;s esophagus develops. 
     Applicant started by focusing on early development of the foregut and esophagus. Applicant utilized a dox-inducible CDX2 construct that is stably transduced in hPSCs, which are then used to generate HEOs ( FIG. 3A-3B ). First, anterior foregut (AFG) cultures were treated for 1 day with doxycycline at varying doses to gauge the appropriate concentration required to induce CDX2 in most cells, which seemed to saturate around 100-500 ng/mL ( FIG. 3C-3E ). Interestingly, SOX2 expression was not repressed by brief (24 hour) induction of CDX2 in anterior foregut cells, suggesting that CDX2 (alone) does not directly repress SOX2 transcription ( FIG. 3C -3D). 
     Continuing doxycycline treatment for the first month in HEOs outgrowth resulted in HEOs upregulating some intestinal markers, such as CDX1 and CDH17, while MUC2 remained unchanged ( FIG. 3G-3J ). The stratified squamous marker p63 was repressed, and SOX2 appears modestly downregulated, which is consistent with earlier results in the day 6 anterior foregut cultures ( FIG. 3D, 3K-3L ). Additionally, stratified squamous markers KRT5 and KRT13 were unchanged by CDX2 induction in the developing HEOs (data not shown). To further examine the regulatory interplay between these two primary transcription factors—SOX2 in the foregut and CDX2 in the hindgut—Applicant induced SOX2 in the human intestinal organoids (HIOs) ( FIG. 8A-8B ). In these cultures, Applicant found that treatment of HIOs with SOX2 resulted in upregulation of stratified squamous markers p63 and KRT13 (mildly), as well as downregulation of CDH17 and CDX2 ( FIG. 8C-E , 8 G- 8 H). In the SOX2-induced HIOs, there is also upregulation of CLDN18, a marker expressed in the stomach, though it is important to note that some variability exists in control HIOs ( FIG. 8C , data not shown). PDX1, a distal stomach or proximal intestine marker, trends towards downregulation with SOX2-induction, though its expression is also often variable in control HIOs ( FIG. 8F ). Together, these data suggest that while SOX2 exerts a stronger effect to inhibit the mid/hindgut fate, CDX2 alone is unable to robustly repress the foregut/esophageal fate during early development. 
     To determine whether the regulatory actions of CDX2 persist later in development (or in the HEO protocol) when plasticity is classically thought to be increasingly limited, Applicant grew HEOs to 6 weeks of age and treated with doxycycline for 8 days ( FIG. 4A ). In this case, SOX2 and p63 were downregulated in response to CDX2 induction, though there were some HEOs that minimally responded and/or had minimal CDX2 induction ( FIG. 4B-4E , data not shown). Due to the variability in the CDX2-inducible system, Applicant opted for an analysis at the cellular resolution. Applicant counted and binned cells into 3 categories: uninduced, CDX2-low (induced), and CDX2-high (induced) ( FIG. 4F-4G ). Restricting the analysis to the basal cells, both SOX2 and p63 are strongly repressed in CDX2-high basal cells, while many cells can co-express SOX2 or p63 with CDX2 in CDX2-low basal cells ( FIG. 4H-4I ). This suggests that if all cells expressed CDX2 at high levels, these key esophageal transcription factors would be effectively repressed. 
     To further examine the role of CDX2 in repressing the esophageal (stratified squamous) epithelial identity, Applicant examined differentiated markers of the esophagus with CDX2-induction as well as in conjunction with DAPT, a Notch (γ-secretase) inhibitor ( FIG. 5A ). HESS, a target gene of Notch signaling in the esophagus, is downregulated upon DAPT addition ( FIG. 5F ). KRT5 is downregulated with CDX2-induction, and further downregulated with DAPT addition, as evident by some organoids completely losing KRT5 expression ( FIG. 5B,5H ). KRT13 is also downregulated, though there does not appear to be a synergistic effect with DAPT treatment ( FIG. 5C ). More differentiated markers IVL and CRNN are downregulated in CDX2-induced HEOs with or without DAPT treatment ( FIG. 5D,5H ). Finally, CDH17 appears to be modestly upregulated with CDX2-induction, though it was rare to find organoids that had visible protein expression of CDH17 ( FIG. 5E,5H ). This suggests that CDX2 is able to repress stratified squamous epithelial markers, with inhibition of Notch minimally adding to this effect. 
     Because BMP signaling has been implicated in the transformation of esophageal into intestinal cells, Applicant also examined the effects of BMP signaling in HEOs ( FIG. 9A ) (Mari et al., 2014). Treating 6-week-old HEOs with BMP4 for additional 2 weeks results in loss of stratification and expression of differentiation markers ( FIG. 9B, 9G-9J ). The remaining basal cells have active BMP signaling (pSMAD1/5/9+) and express p63, but loss expression of SOX2 ( FIG. 9B, 9D-9E ). Additionally, there was minimal EdU incorporation in BMP4 treated HEOs, meaning that cell turnover has dramatically slowed down ( FIG. 9B-9C ). CDX2 expression was unchanged in BMP4 treated HEOs, though CDX2-induction results in downregulation of ID1, a BMP target ( FIG. 5G , data not shown). Together, this suggests that BMP signaling may reinforce the downregulation of stratified squamous epithelium by counteracting the dampening in BMP signaling when CDX2 is induced. 
     Modeling Eosinophilic Esophagitis Using HEOs 
     Finally, Applicant tested whether HEOs could be used to model eosinophilic esophagitis, an inflammatory disease affecting the esophagus. Applicant focused on the epithelial response to IL-13, a cytokine known to enact broad changes in the esophagus, to validate HEOs in modeling eosinophilic esophagitis. Applicant treated 6-8-week-old HEOs with IL-13 for various durations and examined multiple properties of the HEOs ( FIG. 6A ). First, Applicant validated the response of target genes CCL26, CDH26, CAPN14, and SERPINB4 to a short duration of IL-13 treatment ( FIG. 6B-6E ). Extended treatment with IL-13 maintained upregulation of some target genes SERPINB13 and CDH26 ( FIG. 6F ). In addition to the upregulation of these target genes, EdU incorporation was increased in the basal-most p63+ cells, suggesting that the basal cells are more proliferative with extended exposure to IL-13 ( FIG. 6G-6H ). 
     Applicant next looked at the morphology and differentiation of the stratified squamous epithelium upon treatment with IL-13. HEOs treated with IL-13 downregulated late differentiation and structural proteins DSG1, IVL, and CRNN, though the control organoids had significant variability in the expression of these differentiated markers by RNA ( FIG. 7A-7D ). Additionally, the epithelium had dilated intercellular spaces suprabasally, and using electron microscopy, there were increased spaces between individual cells and a decrease in cell-cell contacts ( FIG. 7A,7G ). These data suggest that, for the most part, HEOs respond as expected to IL-13 treatments when compared to other model systems. 
     Lastly, because BMP signaling has also been implicated in eosinophilic esophagitis, particularly that the BMP antagonist follistatin is downregulated in the diseased esophagus, Applicant examined whether BMP activation can reverse some aspects of the disease process (Jiang et al., 2015). However, unlike the mouse esophagus induced with IL-13, HEOs did not upregulate BMP antagonists NOG and FST ( FIG. 7E-F ) (Jiang et al., 2015). This is reflected by the mild increase in BMP target gene ID3 to IL-13 (and BMP4) treatment ( FIG. 7L ). Despite this, upon treatment of HEOs with IL-13 and BMP4 compared to just IL-13, the expression of SOX2 and PTCH1 normalizes back to control ( FIG. 7H,7K ). IL-13 targets CCL26 and CDH26 were also downregulated with BMP4 addition ( FIG. 7I-7J ). However, stratified squamous markers KRT5, KRT13, IVL, and CRNN were not consistently altered with the addition of BMP4 and IL-13 compared to IL-13 treatment alone (data not shown). Thus, BMP signaling activation may reverse or counter some aspects of the disease process induced by IL-13. 
     The results shared some similarities with previously published experiments. In contrast to the hypomorphic Sox2 model, which had low Sox2 levels for the entirety of embryonic development, Applicant was able to carefully examine when and for which processes are Sox2 necessary in esophageal development. Thus, Applicant was able to distinguish that the basal layer of the esophagus appeared intact in mid-embryonic (E11.5) knockout of Sox2 by expression of Krt14 and p63, while the esophagus in earlier knockouts (E8.5) or in hypomorphic Sox2 embryos had reduced/absent expression of these proteins (Que et al., 2007). The result may be due to the establishment of p63 expression in the esophagus by the time of the later Sox2 knockout, which then p63 alone may be able to maintain basal development. Another difference between the global Sox2 hypomorphs and mid-embryonic Sox2 knockout was that the later Sox2 knockout esophagi did not appear to acquire a different tissue identity (intestine, gastric, respiratory), suggesting that establishment of the esophageal fate has been set by E11.5. Interestingly, the results also show that Sox2 loss at E11.5 resulted in loss of suprabasal differentiation and increased suprabasal proliferation, which is similar to how Sox2 may suppress proliferation during stomach development (Hagey et al., 2018). Late-embryonic or early-postnatal knockout of Sox2 appeared to have minimal effect on the esophagus, which suggest that Sox2 may not play a major role in the adult esophagus, more closely resembling the stomach compared to the trachea (Que et al., 2009; Sarkar et al., 2016). Therefore, though the esophageal fate may be set by mid-embryonic development, the results demonstrate that continued Sox2 expression after initial patterning of the anterior foregut is required for proper esophageal differentiation and maturation. However, longer-term studies with more mice as well as injury models may uncover a later role for Sox2 in the late embryonic and post-natal esophagus. 
     For the other diseases, Fanconi anemia, Barrett&#39;s esophagus, and eosinophilic esophagitis, Applicant attempted to use HEOs to model the changes in the esophagus. In trying to model esophageal atresia in Fanconi anemia with HEOs, a primary obstacle is that only a minority of patients with Fanconi anemia have GI malformations. The particular patient used to generate the iPS line in this study did not have esophageal atresia, though FANCA mutations have been linked to esophageal atresia (Feng et al., 2018). Because loss of FANCA results in increased sensitivity to DNA damage, Applicant examined cell death (by cleaved Caspase 3 staining), but found no difference (or more precisely, no significant amount of cell death in either case), which may be expected since Applicant did not add any chemotherapeutic agents. Interestingly, despite the smaller size of the FANCA-deficient HEOs, there were more proliferative cells compared to control HEOs, which is similar to the results found in FANCA-deficient skin keratinocytes in culture (Hoskins et al., 2009). Apart from this difference though, Applicant did not find changes in differentiation. One caveat with using HEOs to model esophageal atresia is that the culture conditions may compensate for or complement the deficiency, which could bypass the majority of the disease process. Additionally, the analysis at the 1-month time point may be too late in that the deficiency may have had most of its effects in the earlier stages of the protocol. 
     Applicant next sought to model Barrett&#39;s esophagus using HEOs. In the older HEOs, Applicant found that CDX2-induction leads to downregulation of some stratified squamous markers, which contrasts the minimal changes that resulted in a similar experiment performed in an esophageal keratinocyte line (EPC2) (Mari et al., 2014). Applicant&#39;s results aligned with the inability of CDX2-induction to robustly upregulate of intestinal genes, suggesting the requirement of additional factors, as shown by using a DNA-methyltransferase inhibitor in other models (Kong et al., 2009, 2011; Mari et al., 2014). Notch inhibition only appeared to mildly (or negligibly) add to this transformation in the HEOs, unlike a previous study using organotypic raft cultures (Vega et al., 2014). Applicant similarly found that BMP activation also downregulates stratified squamous genes, although in our case, this may be mediated by the cell cycle arrest of the stem/progenitor cells (Mari et al., 2014). 
     Applicant also induced CDX2 and SOX2 in the HEO or HIO differentiation protocols (respectively) to examine the transcriptional network that regulates this switch between fates. Consistent with studies in mice, SOX2 induction in HIOs downregulate CDX2 and upregulate genes of various foregut lineages, p63, KRT13, and CLDN18, though the epithelium still is predominantly columnar (Kuzmichev et al., 2012). Interestingly, brief CDX2 induction in early foregut cultures does not directly regulate/repress SOX2 expression, and it has been shown in the early endoderm that some SOX2+ CDX2+ double-positive cells exist (Sherwood et al., 2009). However, extending cultures and CDX2-induction to early (or late) HEOs results in repression of SOX2 and p63, suggesting CDX2 may alter downstream targets that then regulate SOX2 and p63. Also, beginning CDX2-induction early results in significant upregulation of CDH17, unlike later CDX2-induction, suggesting that there is some plasticity earlier on which is lost as the organoids mature. Thus, this suggests that multiple changes are required to fully transform an esophageal epithelium into intestinal epithelium, or vice-versa. Alternatively, the cells that give rise to the metaplasia in Barrett&#39;s esophagus may not be the stratified squamous epithelium. 
     Finally, modeling the epithelial changes in eosinophilic esophagitis using HEOs may be done. Treating HEOs with IL-13 resulted in similar responses using IL-13 treated air-liquid interface (ALI) esophageal cultures, such as downregulation of differentiated stratified squamous epithelial genes (Blanchard et al., 2010; K C et al., 2015). Additionally, the increased proliferation in IL-13 treated HEOs may indicate the start of basal cell hyperplasia, though, in HEOs, the actual thickening of the basal layer is difficult to assess and may not occur, as the organoid would be able to freely expand being suspended in three-dimensional culture. Similar to other studies, signs of barrier dysfunction can be observed, including the increased intercellular spaces and downregulation of DSG1, though barrier function was not directly assessed through measuring the transepithelial electrical resistance (TEER) as in ALI cultures (D&#39;Mello et al., 2016; Davis et al., 2016; Kasagi et al., 2018). Thus, it appears that HEOs respond expectedly to IL-13 treatment. 
     Various signaling pathways that might be misregulated in eosinophilic esophagitis were investigated. In human biopsies of eosinophilic esophagitis and an experiment where IL-13 was misexpressed in the mouse esophagus, BMP signaling was reduced and the BMP antagonist, follistatin, was upregulated (Jiang et al., 2015). However, Applicant found a mild, but opposite, change in BMP antagonists and BMP activation in HEOs treated with IL-13. Interestingly though, BMP activation in IL-13 treated HEOs reverses some changes that occur in HEOs treated with IL-13 alone, as evident by downregulation SOX2 and some IL-13 target genes. Additionally, using PTCH1 as a read-out for hedgehog signaling activity, IL-13 treatment upregulates PTCH1 (Robbins et al., 2012). This potential increase in hedgehog signaling may be linked to the increase in proliferation and decreased differentiation of the epithelium, which resembles a study with Ptch1 mutant mouse esophagi and in esophageal squamous cell carcinoma (van Dop et al., 2012). Through modeling these select esophageal pathologies, Applicant has demonstrated that HEOs can be used as a complementary model to better understand the mechanisms underlying these and hopefully other diseases affecting the esophagus. 
     Materials and Methods 
     Mice 
     Wild-type and mutant mice were used for studies on foregut and esophageal development. Sox2 fl/fl  mice were obtained from Richard Lang&#39;s lab (Shaham et al., 2009), and Sox2CreER (stock #017593, Arnold et al., 2011) were obtained from The Jackson Laboratory. Pregnant dams were gavaged at various stages with tamoxifen at 0.12 mg/g mouse to activate the CreER at appropriate stages. Mice were housed in the animal facility at Cincinnati Children&#39;s Hospital Medical Center (CCHMC) in accordance with NIH Guidelines for the Care and Use of Laboratory animals. Animals were maintained on a 12 hour light-dark cycle with access to water and standard chow ad libitum. Healthy animals were used for all experiments. All experiments were performed under the approval of the Institutional Animal Care and Use Committee of CCHMC (protocols IACUC2016-0004). 
     Human ESC/IPSC and Maintenance 
     Human embryonic stem cell (hESC) line H1 (WA01, male) were purchased from WiCell. iPSC line iPS106 was generated in-house and approved by the institutional review board at CCHMC. All hPSCs were maintained on feeder-free cultures: cells were plated on hESC-qualified Matrigel (BD Biosciences, San Jose, Calif.) and maintained at 37° C. with 5% CO 2  with daily replacement of mTeSR1 media (STEMCELL Technologies, Vancouver, Canada); cells were passaged routinely every 4 days using Dispase (STEMCELL Technologies). The HA-tagged SOX2, CDX2, or FANCA dox-inducible lines were generated by first cloning the human SOX2 ORF, CDX2 ORF, or FANCA ORF into pINDUCER20 (respectively) (Addgene #44012, Meerbrey et al., 2011). Next, lentivirus was generated with help of the Viral Vector Core Facility at CCHMC. The lentivirus for HA-SOX2 and CDX2 were transduced into hESCs with 2 μL of virus; these lines were maintained on selection with mTeSR1 and G418 (500 μg mL-1, ThermoFisher Scientific). The lentivirus for FANCA were transduced prior to the iPS106 line generation, as FANCA is required for maintenance of hPSC properties. The hESC H1 line (and transduced derivatives) was used in all experiments excluding Fanconi Anemia modeling in HEOs, which used the iPS106 line. 
     Differentiation of Anterior Foregut Cultures and Spheroids 
     Confluent hPSC cultures were treated with Acutase (STEMCELL Technologies) to resuspend as single cells in mTeSR1 and Y-27632 (10 μM, Tocris) and plated on Matrigel. On the following day, differentiation into definitive endoderm was carried out as previously described (McCracken et al., 2014). Briefly, cells were treated with Activin A (100 ng mL-1, R&amp;D systems, Minneapolis, Minn.) and BMP4 (50 ng mL-1, R&amp;D systems) on the first day in RPMI 1640 media (Life Technologies). Cells in the following two days were treated with only Activin A (100 ng mL-1) in RPMI 1640 with increasing concentrations 0.2% and 2% of HyClone defined fetal bovine serum (dFBS, GE Healthcare Life Sciences). 
     For the generation of anterior foregut spheroids, from definitive endoderm, cells were treated with Wnt3a (500 ng mL-1, R&amp;D systems) for 2 days, and FGF4 (500 ng mL-1, R&amp;D systems), Noggin (200 ng mL-1) for 3 days in RPMI 1640 with 2% dFBS. Three-dimensional culture and differentiation of anterior foregut spheroids into human esophageal organoids were obtained as described above. 
     Immunofluoresence Analysis 
     Tissue cultures were fixed with 4% paraformaldehyde at either room temperature for 15 minutes (for monolayer cultures), or 4° C. for overnight (for organoids). Tissues were thoroughly washed in PBS and stained for monolayer cultures, while organoids were thoroughly washed and then left in 30% sucrose overnight, embedded in OCT compound (VWR), and sectioned at a thickness of 8 μm. Slides were then permeabilized with 0.5% TritonX-100 in PBS for 10 minutes, blocked in 5% normal donkey serum (Jackson ImmunoResearch) for 1 hour minimum, and incubated in primary antibody overnight at 4° C. On the next day, slides were thoroughly washed in PBS, incubated in secondary antibody (at 1:500) for 1 hour, and then thoroughly washed again. For EdU visualization, the Click-iT EdU Alexa Fluor 488 Imaging Kit (Invitrogen) was used prior to blocking. Antibodies and dilutions used are shown in Table 1. 
     RNA Isolation and qPCR 
     Monolayer cultures and organoids were harvested in total, including the plated/embedding matrigel. Total RNA was isolated using the NucleoSpin RNA kit (Macherey-Nagel) and reverse transcribed to cDNA using the SuperScript VILO cDNA synthesis kit (ThermoFisher Scientific). For qRT-PCR, Applicant used Quantitect SYBR-Green master mix (Qiagen) and ran the reaction on a QuantStudio 6 machine (ThermoFisher Scientific). Primers used are shown in Table 2. 
     REFERENCES 
     
         
         Andl, C. D., Mizushima, T., Nakagawa, H., Oyama, K., Harada, H., Chruma, K., Herlyn, M., and Rustgi, A. K. (2003). Epidermal growth factor receptor mediates increased cell proliferation, migration, and aggregation in esophageal keratinocytes in vitro and in vivo. Journal of Biological Chemistry, 278(3), 1824-1830. https://doi.org/10.1074/jbc.M209148200 
         Arnold, K., Sarkar, A., Yram, M. A., Polo, J. M., Bronson, R., Sengupta, S., Seandel, M., Geijsen, N., and Hochedlinger, K. (2011). Sox2+ Adult Stem and Progenitor Cells Are Important for Tissue Regeneration and Survival of Mice. Cell Stem Cell, 9(4), 317-329. https://doi.org/10.1016/j.stem.2011.09.001 Bamberger, C., Pollet, D., and Schmale, H. (2002). Retinoic acid inhibits downregulation of DeltaNp63alpha expression during terminal differentiation of human primary keratinocytes. The Journal of Investigative Dermatology, 118(1), 133-8. https://doi.org/10.1046/j.0022-202x.2001.01649.x 
         Bayha, E., Jorgensen, M. C., Serup, P., and Grapin-Botton, A. (2009). Retinoic acid signaling organizes endodermal organ specification along the entire antero-posterior axis. PloS One, 4(6), e5845. https://doi.org/10.1371/journal.pone.0005845 
         Chen, H., Li, J., Li, H., Hu, Y., Tevebaugh, W., Yamamoto, M., Que, J., and Chen, X. (2012). Transcript profiling identifies dynamic gene expression patterns and an important role for Nrf2/Keap1 pathway in the developing mouse esophagus. PloS One, 7(5), e36504. https://doi.org/10.1371/journal.pone.0036504 
         Chen, Y.-W., Huang, S. X., de Carvalho, A. L. R. T., Ho, S.-H., Islam, M. N., Volpi, S., Notarangelo, L. D., Ciancanelli, M., Casanova, J.-L., Bhattacharya, J., Liang, A. F., et al. (2017). A three-dimensional model of human lung development and disease from pluripotent stem cells. Nature Cell Biology, 19(5), 542-549. https://doi.org/10.1038/ncb3510 
         Chen, Y., Shi, L., Zhang, L., Li, R., Liang, J., Yu, W., Sun, L., Yang, X., Wang, Y., Zhang, Y., and Shang, Y. (2008). The Molecular Mechanism Governing the Oncogenic Potential of SOX2 in Breast Cancer. Journal of Biological Chemistry, 283(26), 17969-17978. https://doi.org/10.1074/jbc.M802917200 
         D&#39;Amour, K. a, Agulnick, A. D., Eliazer, S., Kelly, O. G., Kroon, E., and Baetge, E. E. (2005). Efficient differentiation of human embryonic stem cells to definitive endoderm. Nature Biotechnology, 23(12), 1534-1541. https://doi.org/10.1038/nbt1163 
         Daniely, Y., Liao, G., Dixon, D., Linnoila, R. I., Lori, A., Randell, S. H., Oren, M., and Jetten, A. M. (2004). Critical role of p63 in the development of a normal esophageal and tracheobronchial epithelium. American Journal of Physiology. Cell Physiology, 287(1), C171-C181. https://doi.org/10.1152/ajpcell.00226.2003 Davenport, C., Diekmann, U., Budde, I., Detering, N., and Naujok, O. (2016). The Anterior-Posterior Patterning of Definitive Endoderm Generated from Human Embryonic Stem Cells Depends on the Differential Signaling of Retinoic Acid, Wnt- and BMP-Signaling. Stem Cells, 34(11), 2635-2647. https://doi.org/10.1002/stem.2428 
         Dessimoz, J., Opoka, R., Kordich, J. J., Grapin-Botton, A., and Wells, J. M. (2006). FGF signaling is necessary for establishing gut tube domains along the anterior-posterior axis in vivo. Mechanisms of Development, 123(1), 42-55. https://doi.org/10.1016/j.mod.2005.10.001 
         DeWard, A. D., Cramer, J., and Lagasse, E. (2014). Cellular heterogeneity in the mouse esophagus implicates the presence of a nonquiescent epithelial stem cell population. Cell Reports, 9(2), 701-11. https://doi.org/10.1016/j.celrep.2014.09.027 
         Domyan, E. T., Ferretti, E., Throckmorton, K., Mishina, Y., Nicolis, S. K., and Sun, X. (2011). Signaling through BMP receptors promotes respiratory identity in the foregut via repression of Sox2. Development (Cambridge, England), 138(5), 971-981. https://doi.org/10.1242/dev 0.053694 
         Doupe, D. P., Alcolea, M. P., Roshan, A., Zhang, G., Klein, a. M., Simons, B. D., and Jones, P. H. (2012). A Single Progenitor Population Switches Behavior to Maintain and Repair Esophageal Epithelium. Science, 337(6098), 1091-1093. https://doi.org/10.1126/science.1218835 
         Dye, B. R., Dedhia, P. H., Miller, A. J., Nagy, M. S., White, E. S., Shea, L. D., and Spence, J. R. (2016). A bioengineered niche promotes in vivo engraftment and maturation of pluripotent stem cell derived human lung organoids. ELife, 5(Septem ber2016). https://doi.org/10.7554/eLife.19732 
         Dye, B. R., Hill, D. R., Ferguson, M. A., Tsai, Y.-H., Nagy, M. S., Dyal, R., Wells, J. M., Mayhew, C. N., Nattiv, R., Klein, O. D., White, E. S., et al. (2015). In vitro generation of human pluripotent stem cell derived lung organoids. ELife, 4, e05098. https://doi.org/10.7554/eLife.05098 
         Fantes, J., Ragge, N. K., Lynch, S.-A., McGill, N. I., Collin, J. R. O., Howard-Peebles, P. N., Hayward, C., Vivian, A. J., Williamson, K., van Heyningen, V., and FitzPatrick, D. R. (2003). Mutations in SOX2 cause anophthalm ia. Nature Genetics, 33(4), 461-463. https://doi.org/10.1038/ng1120 
         Fausett, S. R., Brunet, L. J., and Klingensmith, J. (2014). BMP antagonism by Noggin is required in presumptive notochord cells for mammalian foregut morphogenesis. Developmental Biology, 391(1), 111-24. https://doi.org/10.1016/j.ydbio.2014.02.008 
         Goss, A. M., Tian, Y., Tsukiyama, T., Cohen, E. D., Zhou, D., Lu, M. M., Yamaguchi, T. P., and Morrisey, E. E. (2009). Wnt2/2b and beta-catenin signaling are necessary and sufficient to specify lung progenitors in the foregut. Developmental Cell, 17(2), 290-8. https://doi.org/10.1016/j.devcel.2009.06.005 
         Green, M. D., Chen, A., Nostro, M.-C., d&#39;Souza, S. L., Schaniel, C., Lemischka, I. R., Gouon-Evans, V., Keller, G., and Snoeck, H.-W. (2011). Generation of anterior foregut endoderm from human embryonic and induced pluripotent stem cells. Nature Biotechnology, 29(3), 267-72. https://doi.org/10.1038/nbt.1788 Harris-Johnson, K. S., Domyan, E. T., Vezina, C. M., and Sun, X. (2009). beta-Catenin promotes respiratory progenitor identity in mouse foregut. Proceedings of the National Academy of Sciences of the United States of America, 106(38), 16287-92. https://doi.org/10.1073/pnas.0902274106 
         Hoskins, E. E., Morris, T. A., Higginbotham, J. M., Spardy, N., Cha, E., Kelly, P., Williams, D. A., Wikenheiser-Brokamp, K. A., Duensing, S., and Wells, S. I. (2009). Fanconi anemia deficiency stimulates HPV-associated hyperplastic growth in organotypic epithelial raft culture. Oncogene, 28(5), 674-685. https://doi.org/10.1038/onc.2008.416 
         Jho, E., Zhang, T., Domon, C., Joo, C.-K., Freund, J.-N., and Costantini, F. (2002). Wnt/beta-catenin/Tcf signaling induces the transcription of Axin2, a negative regulator of the signaling pathway. Molecular and Cellular Biology, 22(4), 1172-83. https://doi.org/10.1128/MCB.22.4.1172 
         Kalabis, J., Oyama, K., Okawa, T., Nakagawa, H., Michaylira, C. Z., Stairs, D. B., Figueiredo, J., Mahmood, U., Diehl, J. A., Herlyn, M., and Rustgi, A. K. (2008). A subpopulation of mouse esophageal basal cells has properties of stem cells with the capacity for self-renewal and lineage specification. Journal of Clinical Investigation, (118), 3860-3869. https://doi.org/10.1172/JCI35012 
         Kalabis, J., Wong, G. S., Vega, M. E., Natsuizaka, M., Robertson, E. S., Herlyn, M., Nakagawa, H., and Rustgi, A. K. (2012). Isolation and characterization of mouse and human esophageal epithelial cells in 3D organotypic culture. Nature Protocols, 7(2), 235-246. https://doi.org/10.1038/nprot.2011.437 
         Kasagi, Y., Chandramouleeswaran, P. M., Whelan, K. A., Tanaka, K., Giroux, V., Sharma, M., Wang, J., Benitez, A. J., DeMarshall, M., Tobias, J. W., Hamilton, K. E., et al. (2018). The Esophageal Organoid System Reveals Functional Interplay Between Notch and Cytokines in Reactive Epithelial Changes. Cmgh, 5(3), 333-352. https://doi.org/10.1016/j.jcmgh.2017.12.013 
         Kearns, N. a, Genga, R. M. J., Ziller, M., Kapinas, K., Peters, H., Brehm, M. a, Meissner, A., and Maehr, R. (2013). Generation of organized anterior foregut epithelia from pluripotent stem cells using small molecules. Stem Cell Research, 11(3), 1003-12. https://doi.org/10.1016/j.scr.2013.06.007 
         Kormish, J. D., Sinner, D., and Zorn, A. M. (2010). Interactions between SOX factors and Wnt/beta-catenin signaling in development and disease. Developmental Dynamics: An Official Publication of the American Association of Anatomists, 239(August 2009), 56-68. https://doi.org/10.1002/dvdy.22046 Li, H., Zhou, H., Fu, X., and Xiao, R. (2016). Directed differentiation of human embryonic stem cells into keratinocyte progenitors in vitro: an attempt with promise of clinical use. In vitro Cellular &amp; Developmental Biology—Animal, 52(8), 885-893. https://doi.org/10.1007/s11626-016-0024-2 
         Longmire, T. a, Ikonomou, L., Hawkins, F., Christodoulou, C., Cao, Y., Jean, J. C., Kwok, L. W., Mou, H., Rajagopal, J., Shen, S. S., Dowton, A. a, et al. (2012). Efficient derivation of purified lung and thyroid progenitors from embryonic stem cells. Cell Stem Cell, 10(4), 398-411. https://doi.org/10.1016/j.stem.2012.01.019 
         Lustig, B., Jerchow, B., Sachs, M., Weiler, S., Pietsch, T., Karsten, U., van de Wetering, M., Clevers, H., Schlag, P. M., Birchmeier, W., and Behrens, J. (2002). Negative feedback loop of Wnt signaling through upregulation of conductin/axin2 in colorectal and liver tumors. Molecular and Cellular Biology, 22(4), 1184-93. https://doi.org/10.1128/MCB.22.4.1184 
         Mandegar, M. A., Huebsch, N., Frolov, E. B., Shin, E., Truong, A., Olvera, M. P., Chan, A. H., Miyaoka, Y., Holmes, K., Spencer, C. I., Judge, L. M., et al. (2016). CRISPR Interference Efficiently Induces Specific and Reversible Gene Silencing in Human iPSCs. Cell Stem Cell, 18(4), 541-553. https://doi.org/10.1016/j.stem.2016.01.022 
         Matt, N., Ghyselinck, N. B., Wendling, O., Chambon, P., and Mark, M. (2003). Retinoic acid-induced developmental defects are mediated by RARβ/RXR heterodimers in the pharyngeal endoderm. Development, 130(10), 2083-2093. https://doi.org/10.1242/dev 0.00428 
         McCauley, H. A., and Wells, J. M. (2017). Pluripotent stem cell-derived organoids: using principles of developmental biology to grow human tissues in a dish. Development, 144(6), 958-962. https://doi.org/10.1242/dev.140731 
         McCracken, K. W., Aihara, E., Martin, B., Crawford, C. M., Broda, T., Treguier, J., Zhang, X., Shannon, J. M., Montrose, M. H., and Wells, J. M. (2017). Wnt/β-catenin promotes gastric fundus specification in mice and humans. Nature, 541(7636), 182-187. https://doi.org/10.1038/nature21021 
         McCracken, K. W., Catá, E. M., Crawford, C. M., Sinagoga, K. L., Schumacher, M., Rockich, B. E., Tsai, Y.-H., Mayhew, C. N., Spence, J. R., Zavros, Y., and Wells, J. M. (2014). Modelling human development and disease in pluripotent stem-cell-derived gastric organoids. Nature, 516(7531), 400-404. https://doi.org/10.1038/nature13863 
         McLin, V. a, Rankin, S. a, and Zorn, A. M. (2007). Repression of Wnt/beta-catenin signaling in the anterior endoderm is essential for liver and pancreas development. Development (Cambridge, England), 134(12), 2207-17. https://doi.org/10.1242/dev 0.001230 
         Meerbrey, K. L., Hu, G., Kessler, J. D., Roarty, K., Li, M. Z., Fang, J. E., Herschkowitz, J. I., Burrows, A. 
         Ciccia, A., Sun, T., Schmitt, E. M., et al. (2011). The pINDUCER lentiviral toolkit for inducible RNA interference in vitro and in vivo. Proceedings of the National Academy of Sciences of the United States of America, 108(9), 3665-3670. https://doi.org/10.1073/pnas.1019736108 
         Múnera, J. O., Sundaram, N., Rankin, S. A., Hill, D., Watson, C., Mahe, M., Vallance, J. E., Shroyer, N. Sinagoga, K. L., Zarzoso-Lacoste, A., Hudson, J. R., et al. (2017). Differentiation of Human Pluripotent Stem Cells into Colonic Organoids via Transient Activation of BMP Signaling. Cell Stem Cell, 21(1), 51-64.e6. https://doi.org/10.1016/j.stem.2017.05.020 
         Niederreither, K., Subbarayan, V., Dolle, P., and Chambon, P. (1999). Embryonic retinoic acid synthesis is essential for early mouse post-implantation development. Nature Genetics, 21(4), 444-448. https://doi.org/10.1038/7788 
         Park, E. J., Sun, X., Nichol, P., Saijoh, Y., Martin, J. F., and Moon, A. M. (2008). System for tamoxifen-inducible expression of Cre-recombinase from the Foxa2 locus in mice. Developmental Dynamics, 237(2), 447-453. https://doi.org/10.1002/dvdy.21415 
         Que, J., Choi, M., Ziel, J. W., Klingensmith, J., and Hogan, B. L. M. (2006). Morphogenesis of the trachea and esophagus: current players and new roles for noggin and Bmps. Differentiation, 74(7), 422-437. https://doi.org/10.1111/j.1432-0436.2006.00096.x 
         Que, J., Okubo, T., Goldenring, J. R., Nam, K.-T., Kurotani, R., Morrisey, E. E., Taranova, O., Pevny, L. H., and Hogan, B. L. M. (2007). Multiple dose-dependent roles for Sox2 in the patterning and differentiation of anterior foregut endoderm. Development (Cambridge, England), 134(13), 2521-31. https://doi.org/10.1242/dev.003855 
         Rankin, S. A., Han, L., McCracken, K. W., Kenny, A. P., Anglin, C. T., Grigg, E. A., Crawford, C. M., Wells, J. M., Shannon, J. M., and Zorn, A. M. (2016). A Retinoic Acid-Hedgehog Cascade Coordinates Mesoderm-Inducing Signals and Endoderm Competence during Lung Specification. Cell Reports, 16(1), 66-78. https://doi.org/10.1016/J.CELREP.2016.05.060 
         Rankin, S. a, Gallas, A. L., Neto, A., Gomez-Skarmeta, J. L., and Zorn, A. M. (2012). Suppression of Bmp4 signaling by the zinc-finger repressors Osr1 and Osr2 is required for Wnt/β-catenin-mediated lung specification in  Xenopus . Development (Cambridge, England), 139(16), 3010-20. https://doi.org/10.1242/dev.078220 
         Rosekrans, S. L., Baan, B., Muncan, V., and van den Brink, G. R. (2015). Esophageal development and epithelial homeostasis. American Journal of Physiology—Gastrointestinal and Liver Physiology, 309(4), G216-228. https://doi.org/10.1152/ajpgi.00088.2015 
         Shaham, O., Smith, A. N., Robinson, M. L., Taketo, M. M., Lang, R. a, and Ashery-Padan, R. (2009). Pax6 is essential for lens fiber cell differentiation. Development (Cambridge, England), 136(15), 2567-2578. https://doi.org/10.1242/dev.032888 
         Sherwood, R. I., Chen, T.-Y. A., and Melton, D. (2009). Transcriptional dynamics of endodermal organ formation. Developmental Dynamics: An Official Publication of the American Association of Anatomists, 238(1), 29-42. https://doi.org/10.1002/dvdy.21810 
         Sinner, D., Kordich, J. J., Spence, J. R., Opoka, R., Rankin, S., Lin, S. J., Jonatan, D., Zorn, A. M., and Wells, J. M. (2007). Sox17 and Sox4 differentially regulate beta-catenin/T-cell factor activity and proliferation of colon carcinoma cells. Molecular and Cellular Biology, 27(22), 7802-7815. https://doi.org/10.1128/MCB.02179-06 
         Sive, H., Grainger, R., and Harland, R. (2000). Early Development of  Xenopus laevis : A Laboratory Manual. Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press. 
         Spence, J. R., Mayhew, C. N., Rankin, S. a, Kuhar, M. F., Vallance, J. E., Tolle, K., Hoskins, E. E., Kalinichenko, V. V, Wells, S. I., Zorn, A. M., Shroyer, N. F., and Wells, J. M. (2011). Directed differentiation of human pluripotent stem cells into intestinal tissue in vitro. Nature, 470(7332), 105-109. https://doi.org/10.1038/nature09691 
         Stevens, M. L., Chaturvedi, P., Rankin, S. A., Macdonald, M., Jagannathan, S., Yukawa, M., Barski, A., and Zorn, A. M. (2017). Genomic integration of Wnt/β-catenin and BMP/Smad1 signaling coordinates foregut and hindgut transcriptional programs. Development, 144(7), 1283-1295. https://doi.org/10.1242/dev.145789 
         Subramanian, A., Tamayo, P., Mootha, V. K., Mukherjee, S., Ebert, B. L., Gillette, M. A., Paulovich, A., Pomeroy, S. L., Golub, T. R., Lander, E. S., and Mesirov, J. P. (2005). Gene set enrichment analysis: A knowledge-based approach for interpreting genome-wide expression profiles. Proceedings of the National Academy of Sciences, 102(43), 15545-15550. https://doi.org/10.1073/pnas.0506580102 
         Tiso, N., Filippi, A., Pauls, S., Bortolussi, M., and Argenton, F. (2002). BMP signalling regulates anteroposterior endoderm patterning in zebrafish. Mechanisms of Development, 118(1-2), 29-37. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12351167 
         Tsankov, A. M., Gu, H., Akopian, V, Ziller, M. J., Donaghey, J., Amit, I., Gnirke, A., and Meissner, A. (2015). Transcription factor binding dynamics during human ES cell differentiation. Nature, 518(7539), 344-9. https://doi.org/10.1038/nature14233 
         Van Raay, T. J., Moore, K. B., Iordanova, I., Steele, M., Jamrich, M., Harris, W. A., and Vetter, M. L. (2005). Frizzled 5 signaling governs the neural potential of progenitors in the developing  Xenopus  retina. Neuron, 46(1), 23-36. https://doi.org/10.1016/j.neuron.2005.02.023 
         Wang, Z., Done, P., Cardoso, W. V., and Niederreither, K. (2006). Retinoic acid regulates morphogenesis and patterning of posterior foregut derivatives. Developmental Biology, 297(2), 433-445. https://doi.org/10.1016/j.ydbio.2006.05.019 
         Watanabe, H., Ma, Q., Peng, S., Adelmant, G., Swain, D., Song, W., Fox, C., Francis, J. M., Pedamallu, C. S., DeLuca, D. S., Brooks, A. N., et al. (2014). SOX2 and p63 colocalize at genetic loci in squamous cell carcinomas. Journal of Clinical Investigation, 124(4), 1636-1645. https://doi.org/10.1172/JCI71545 Williamson, K. a., Hever, A. M., Rainger, J., Rogers, R. C., Magee, A., Fiedler, Z., Keng, W. T., Sharkey, F. H., McGill, N., Hill, C. J., Schneider, A., et al. (2006). Mutations in SOX2 cause anophthalmia-esophageal-genital (AEG) syndrome. Human Molecular Genetics, 15(9), 1413-1422. https://doi.org/10.1093/hmg/dd1064 
         Woo, J., Miletich, I., Kim, B.-M., Sharpe, P. T., and Shivdasani, R. a. (2011). Barx1-mediated inhibition of Wnt signaling in the mouse thoracic foregut controls tracheo-esophageal septation and epithelial differentiation. PloS One, 6(7), e22493. https://doi.org/10.1371/journal.pone.0022493 
         Zhang, Y., Jiang, M., Kim, E., Lin, S., Liu, K., Lan, X., and Que, J. (2016). Development and Stem Cells of the Esophagus. Seminars in Cell &amp; Developmental Biology, 66, 25-35. https://doi.org/10.1016/j.semcdb.2016.12.008 
         Zhou, C., Yang, X., Sun, Y., Yu, H., Zhang, Y., and Jin, Y. (2016). Comprehensive profiling reveals mechanisms of SOX2-mediated cell fate specification in human ESCs and NPCs. Cell Research, 26(2), 171-189. https://doi.org/10.1038/cr.2016.15 
         Zorn, A. M., and Wells, J. M. (2007). Molecular Basis of Vertebrate Endoderm Development. In International Review of Cytology (Vol. 259, pp. 49-111). https://doi.org/10.1016/S0074-7696(06)59002-3 Zorn, A. M., and Wells, J. M. (2009). Vertebrate Endoderm Development and Organ Formation. Annual Review of Cell and Developmental Biology, 25(1), 221-251. https://doi.org/10.1146/annurev.cellbio.042308.113344 
         Arnold, K., Sarkar, A., Yram, M. A., Polo, J. M., Bronson, R., Sengupta, S., Seandel, M., Geijsen, N., and Hochedlinger, K. (2011). Sox2+Adult Stem and Progenitor Cells Are Important for Tissue Regeneration and Survival of Mice. Cell Stem Cell, 9(4), 317-329. https://doi.org/10.1016/j.stem.2011.09.001 
         Auerbach, A. D. (2009). Fanconi anemia and its diagnosis. Mutation Research—Fundamental and Molecular Mechanisms of Mutagenesis, 668(1-2), 4-10. https://doi.org/10.1016/j.mrfmmm.2009.01.013 
         Bakker, S. T., de Winter, J. P., and Riele, H. t. (2013). Learning from a paradox: recent insights into Fanconi anaemia through studying mouse models. Disease Models &amp; Mechanisms, 6(1), 40-47. https://doi.org/10.1242/dmm.009795 
         Blanchard, C., Stucke, E. M., Burwinkel, K., Caldwell, J. M., Collins, M. H., Ahrens, A., Buckmeier, B. K., Jameson, S. C., Greenberg, A., Kaul, A., Franciosi, J. P., et al. (2010). Coordinate Interaction between IL-13 and Epithelial Differentiation Cluster Genes in Eosinophilic Esophagitis. The Journal of Immunology, 184(7), 4033-4041. https://doi.org/10.4049/jimmunol.0903069 
         Caldwell, J. M., Paul, M., and Rothenberg, M. E. (2017). Novel immunologic mechanisms in eosinophilic esophagitis. Current Opinion in Immunology, 48, 114-121. https://doi.org/10.1016/j.coi.2017.08.006 
         Chen, X., Jiang, K., Fan, Z., Liu, Z., Zhang, P., Zheng, L., Peng, N., Tong, J., and Ji, G. (2012). Aberrant expression of Wnt and Notch signal pathways in Barrett&#39;s esophagus. Clinics and Research in Hepatology and Gastroenterology, 36(5), 473-483. https://doi.org/10.1016/j.clinre.2012.06.001 
         D&#39;Mello, R. J., Caldwell, J. M., Azouz, N. P., Wen, T., Sherrill, J. D., Hogan, S. P., and Rothenberg, M. E. (2016). LRRC31 is induced by IL-13 and regulates kallikrein expression and barrier function in the esophageal epithelium. Mucosal Immunology, 9(3), 744-756. https://doi.org/10.1038/mi.2015.98 
         Davis, B. P., Stucke, E. M., Khorki, M. E., Litosh, V. A., Rymer, J. K., Rochman, M., Travers, J., Kottyan, L. C., and Rothenberg, M. E. (2016). Eosinophilic esophagitis-linked calpain 14 is an IL-13—induced protease that mediates esophageal epithelial barrier impairment. JCI Insight, 1(4). https://doi.org/10.1172/jci.insight.86355 
         De Jong, E. M., Felix, J. F., De Klein, A., and Tibboel, D. (2010). Etiology of esophageal atresia and tracheoesophageal fistula: “Mind the gap.” Current Gastroenterology Reports, 12(3), 215-222. https://doi.org/10.1007/s11894-010-0108-1 
         De Jonge, P. J. F., Van Blankenstein, M., Grady, W. M., and Kuipers, E. J. (2014). Barrett&#39;s oesophagus: Epidemiology, cancer risk and implications for management. Gut, 63(1), 191-202. https://doi.org/10.1136/gutjnl-2013-305490 
         Fausett, S. R., and Klingensmith, J. (2012). Compartmentalization of the foregut tube: developmental origins of the trachea and esophagus. Wiley Interdisciplinary Reviews. Developmental Biology, 1(2), 184-202. https://doi.org/10.1002/wdev.12 
         Feng, Y., Chen, R., Da, M., Qian, B., and Mo, X. (2018). Identification of rare heterozygous missense mutations in FANCA in esophageal atresia patients using next generation sequencing. Gene, 661(January), 182-188. https://doi.org/10.1016/j.gene.2018.03.097 
         Furuta, G. T., and Katzka, D. A. (2015). Eosinophilic Esophagitis. New England Journal of Medicine, 373(17), 1640-1648. https://doi.org/10.1056/NEJMra1502863 
         Ghatak, S., Reveiller, M., Toia, L., Ivanov, A., Godfrey, T. E., and Peters, J. H. (2013). Bile acid at low pH reduces squamous differentiation and activates EGFR signaling in esophageal squamous cells in 3-D culture. Journal of Gastrointestinal Surgery: Official Journal of the Society for Surgery of the Alimentary Tract, 17(10), 1723-31. https://doi.org/10.1007/s11605-013-2287-1 
         Hagey, D. W., Klum, S., Kurtsdotter, I., Zaouter, C., Topcic, D., Andersson, O., Bergsland, M., and Muhr, J. (2018). SOX2 regulates common and specific stem cell features in the CNS and endoderm derived organs. PLOS Genetics, 14(2), e1007224. https://doi.org/10.1371/journal.pgen.1007224 
         Huo, X., Zhang, H. Y., Zhang, X. I., Lynch, J. P., Strauch, E. D., Wang, J. Y., Melton, S. D., Genta, R. M., Wang, D. H., Spechler, S. J., and Souza, R. F. (2010). Acid and Bile Salt-Induced CDX2 Expression Differs in Esophageal Squamous Cells From Patients With and Without Barrett&#39;s Esophagus. Gastroenterology, 139(1), 194-203.el. https://doi.org/10.1053/j.gastro.2010.03.035 
         Jiang, M., Ku, W., Zhou, Z., Dellon, E. S., Falk, G. W., Nakagawa, H., Wang, M., Liu, K., Wang, J., Katzka, D. a, Peters, J. H., et al. (2015). BMP-driven NRF2 activation in esophageal basal cell differentiation and eosinophilic esophagitis. The Journal of Clinical Investigation, 125(14), 1-12. https://doi.org/10.1172/JCI78850DS1 
         Jiang, M., Li, H., Zhang, Y., Yang, Y., Lu, R., Liu, K., Lin, S., Lan, X., Wang, H., Wu, H., Zhu, J., et al. (2017). Transitional basal cells at the squamous-columnar junction generate Barrett&#39;s oesophagus. Nature, 550(7677), 529-533. https://doi.org/10.1038/nature24269 
         Kasagi, Y., Chandramouleeswaran, P. M., Whelan, K. A., Tanaka, K., Giroux, V., Sharma, Wang, J., Benitez, A. J., DeMarshall, M., Tobias, J. W., Hamilton, K. E., et al. (2018). The Esophageal Organoid System Reveals Functional Interplay Between Notch and Cytokines in Reactive Epithelial Changes. Cmgh, 5(3), 333-352. https://doi.org/10.1016/j.jcmgh.2017.12.013 
         Kazumori, H., Ishihara, S., and Kinoshita, Y. (2009). Roles of caudal-related homeobox gene Cdx1 in oesophageal epithelial cells in Barrett&#39;s epithelium development. Gut, 58(5), 620-628. https://doi.org/10.1136/gut.2008.152975 
         Kazumori, H., Ishihara, S., Rumi, M. A. K., Kadowaki, Y., and Kinoshita, Y. (2006). Bile acids directly augment caudal related homeobox gene Cdx2 expression in oesophageal keratinocytes in Barrett&#39;s epithelium. Gut, 55(1), 16-25. https://doi.org/10.1136/gut.2005.066209 
         KC, K., Rothenberg, M. E., and Sherrill, J. D. (2015). In vitro model for studying esophageal epithelial differentiation and allergic inflammatory responses identifies keratin involvement in eosinophilic esophagitis. PloS One, 10(6), e0127755. https://doi.org/10.1371/journal.pone.0127755 
         Kong, J., Crissey, M. A., Funakoshi, S., Kreindler, J. L., and Lynch, J. P. (2011). Ectopic Cdx2 expression in murine esophagus models an intermediate stage in the emergence of Barrett&#39;s esophagus. PLoS ONE, 6(4), 1-12. https://doi.org/10.1371/journal.pone.0018280 
         Kong, J., Nakagawa, H., Isariyawongse, B. K., Funakoshi, S., Silberg, D. G., Rustgi, A. and Lynch, J. P. (2009). Induction of intestinalization in human esophageal keratinocytes is a multistep process. Carcinogenesis, 30(1), 122-130. https://doi.org/10.1093/carcin/bgn227 
         Kuzmichev, A. N., Kim, S. K., D&#39;Alessio, A. C., Chenoweth, J. G., Wittko, I. M., Campanati, and McKay, R. D. (2012). Sox2 acts through Sox21 to regulate transcription in pluripotent and differentiated cells. Current Biology, 22(18), 1705-1710. https://doi.org/10.1016/j.cub.2012.07.013 
         Leedham, S. J., Preston, S. L., McDonald, S. A. C., Elia, G., Bhandari, P., Poller, D., Harrison, R., Novelli, M. R., Jankowski, J. A., and Wright, N. A. (2008). Individual crypt genetic heterogeneity and the origin of metaplastic glandular epithelium in human Barrett&#39;s oesophagus. Gut, 57(8), 1041-1048. https://doi.org/10.1136/gut.2007.143339 
         Liu, K., Jiang, M., Lu, Y., Chen, H., Sun, J., Wu, S., Ku, W.-Y., Nakagawa, H., Kita, Y., Natsugoe, S., Peters, J. H., et al. (2013). Sox2 Cooperates with Inflammation-Mediated Stat3 Activation in the Malignant Transformation of Foregut Basal Progenitor Cells. Cell Stem Cell, 12(3), 304-315. https://doi.org/10.1016/j.stem.2013.01.007 
         Liu, T., Zhang, X., So, C. K., Wang, S., Wang, P., Yan, L., Myers, R., Chen, Z., Patterson, A. P., Yang, C. S., and Chen, X. (2007). Regulation of Cdx2 expression by promoter methylation, and effects of Cdx2 transfection on morphology and gene expression of human esophageal epithelial cells. Carcinogenesis, 28(2), 488-496. https://doi.org/10.1093/carcin/bgl176 
         Lubinsky, M. (2015). Sonic Hedgehog, VACTERL, and Fanconi anemia: Pathogenetic connections and therapeutic implications. American Journal of Medical Genetics, Part A, 167(11), 2594-2598. https://doi.org/10.1002/ajmg.a.37257 
         Mari, L., Milano, F., Parikh, K., Straub, D., Everts, V., Hoeben, K. K., Fockens, P., Buttar, N. S., and Krishnadath, K. K. (2014). A pSMAD/CDX2 complex is essential for the intestinalization of epithelial metaplasia. Cell Reports, 7(4), 1197-1210. https://doi.org/10.1016/j.celrep.2014.03.074 
         Meerbrey, K. L., Hu, G., Kessler, J. D., Roarty, K., Li, M. Z., Fang, J. E., Herschkowitz, J. I., Burrows, A. E., Ciccia, A., Sun, T., Schmitt, E. M., et al. (2011). The pINDUCER lentiviral toolkit for inducible RNA interference in vitro and in vivo. Proceedings of the National Academy of Sciences, 108(9),3665-3670. https://doi.org/10.1073/pnas.1019736108 
         Nebert, D. W., Dong, H., Bruford, E. A., Thompson, D. C., Joenje, H., and Vasiliou, V. (2016). Letter to the editor for “Update of the human and mouse Fanconi anemia genes.” Human Genomics, 10(1), 25. https://doi.org/10.1186/s40246-016-0081-3 
         Que, J., Luo, X., Schwartz, R. J., and Hogan, B. L. M. (2009). Multiple roles for Sox2 in the developing and adult mouse trachea. Development (Cambridge, England), 136(11), 1899-1907. https://doi.org/10.1242/dev.034629 
         Robbins, D. J., Fei, D. L., and Riobo, N. A. (2012). The Hedgehog Signal Transduction Network. Science Signaling, 5(246), re6-re6. https://doi.org/10.1126/scisignal.2002906 
         Rochman, M., Travers, J., Miracle, C. E., Bedard, M. C., Wen, T., Azouz, N. P., Caldwell, J. M., KC, K., Sherrill, J. D., Davis, B. P., Rymer, J. K., et al. (2017). Profound loss of esophageal tissue differentiation in patients with eosinophilic esophagitis. Journal of Allergy and Clinical Immunology, 140(3), 738-749.e3. https://doi.org/10.1016/j.jaci.2016.11.042 
         Sarkar, A., Huebner, A. J., Sulahian, R., Anselmo, A., Xu, X., Flattery, K., Desai, N., Sebastian, C., Yram, M. A., Arnold, K., Rivera, M., et al. (2016). Sox2 Suppresses Gastric Tumorigenesis in Mice. Cell Reports, 16(7), 1929-1941. https://doi.org/10.1016/j.celrep.2016.07.034 
         van Dop, W. a., Rosekrans, S. L., Uhmann, a., Jaks, V., Offerhaus, G. J. a., van den Bergh Weerman, M. a., Kasper, M., Heijmans, J., Hardwick, J. C. H., Verspaget, H. W., Hommes, D. W., et al. (2012). Hedgehog signalling stimulates precursor cell accumulation and impairs epithelial maturation in the murine oesophagus. Gut, 62(3), 348-57. https://doi.org/10.1136/gutjnl-2011-301141 
         Vega, M. E., Giroux, V. V., Natsuizaka, M., Liu, M., Klein-Szanto, A. J., Stairs, D. B., Nakagawa, H., Wang, K. K., Wang, T. C., Lynch, J. P., and Rustgi, A. K. (2014). Inhibition of notch signaling enhances transdifferentiation of the esophageal squamous epithelium towards a Barrett&#39;s-like metaplasia via KLF4. Cell Cycle, 13(24), 3857-3866. https://doi.org/10.4161/15384101.2014.972875 
         Wang, D. H., Clemons, N. J., Miyashita, T., Dupuy, A. J., Zhang, W., Szczepny, A., Corcoran-Schwartz, I. M., Wilburn, D. L., Montgomery, E. A., Wang, J. S., Jenkins, N. A., et al. (2010). Aberrant Epithelial-Mesenchymal Hedgehog Signaling Characterizes Barrett&#39;s Metaplasia. Gastroenterology, 138(5), 1810-1822.e2. https://doi.org/10.1053/j.gastro.2010.01.048 
         Wu, L., Oshima, T., Li, M., Tomita, T., Fukui, H., Watari, J., and Miwa, H. (2018). Filaggrin and tight junction proteins are crucial for IL-13-mediated esophageal barrier dysfunction. American Journal of Physiology-Gastrointestinal and Liver Physiology, ajpgi.00404.2017. https://doi.org/10.1152/ajpgi.00404.2017 
       
    
     All percentages and ratios are calculated by weight unless otherwise indicated. 
     All percentages and ratios are calculated based on the total composition unless otherwise indicated. 
     It should be understood that every maximum numerical limitation given throughout this specification includes every lower numerical limitation, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this specification will include every higher numerical limitation, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this specification will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein. 
     The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “20 mm” is intended to mean “about 20 mm.” 
     Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications may be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.