bluuebunny/crossref_metadata_2025_split huggingface dataset:
rhomboid and Star interact synergistically to promote EGFR/MAPK signaling during Drosophila wing vein development
Authors: Guichard Annabel , Biehs Brian , Sturtevant Mark A. , Wickline Laura , Chacko Julie , Howard Katherine , Bier Ethan 
Published: April 2021

ABSTRACT
Genes of the ventrolateral group in Drosophila are dedicated to developmental regulation of Egfr signaling in multiple processes including wing vein development. Among these genes, Egfr encodes the Drosophila EGF-Receptor, spitz (spi) and vein (vn) encode EGF-related ligands, and rhomboid (rho) and Star (S) encode membrane proteins. In this study, we show that rho-mediated hyperactivation of the EGFR/MAPK pathway is required for vein formation throughout late larval and early pupal development. Consistent with this observation, rho activity is necessary and sufficient to activate MAPK in vein primordium during late larval and early pupal stages. Epistasis studies using a dominant negative version of Egfr and a ligand-independent activated form of Egfr suggest that rho acts upstream of the receptor. We show that rho and S function in a common aspect of vein development since loss-of-function clones of rho or S result in nearly identical non-autonomous loss-of-vein phenotypes. Furthermore, mis-expression of rho and S in wild-type and mutant backgrounds reveals that these genes function in a synergistic and co-dependent manner. In contrast, spi does not play an essential role in the wing. These data indicate that rho and S act in concert, but independently of spi, to promote vein development through the EGFR/MAPK signaling pathway.
Targeted inactivation of the EGF and amphiregulin genes reveals distinct roles for EGF receptor ligands in mouse mammary gland development
Authors: Luetteke Noreen C. , Qiu Ting Hu , Fssssenton Suzanne E. , Troyer Kelly L. , Riedel Richard F. , Chang Aileen , Lee David C. 
Published: April 2021

SUMMARY
Targeted mice lacking functional EGF or amphiregulin (AR) were derived and bred to the TGFα-knockout to generate mice lacking various combinations of the three ligands. In contrast to EGF receptor (EGFR) knockout mice, triple null mice lacking half of the EGFR ligand family were healthy and fertile, indicative of overlapping or compensatory functions among EGF family members. Nevertheless, pups born to triple null dams frequently died or were runted, suggesting a mammary gland defect. Comparison of individual and combinatorial knockouts established that specific loss of AR severely stunted ductal outgrowth during puberty, consistent with dramatic expression of AR transcripts in normal developing ducts. Surprisingly, loss of all three ligands did not significantly affect cellular proliferation, apoptosis, or ERK activation within terminal end buds. Following pregnancy, most AR single null females, but few triple null females could nurse their young, revealing collaborative roles for EGF and TGFα in mammopoiesis and lactogenesis. In triple null glands, alveoli were poorly organized and differentiated, and milk protein gene expression was decreased. Additionally, Stat5a activation was frequently reduced in AR single and combinatorial nulls in association with impaired lactation. Collectively, our results provide genetic confirmation of a requirement for EGFR signaling throughout the development of the mouse mammary gland, and reveal stage-dependent activities for different EGFR ligands. Finally, the additional loss of growth factors from pups nursed by triple null dams further worsened their survival and growth, establishing functions for both maternal- and neonatal-derived growth factors.
Signalling by the RET receptor tyrosine kinase and its role in the development of the mammalian enteric nervous system
Authors: Taraviras Stavros , Marcos-Gutierrez Camelia V. , Durbec Pascale , Jani Harsha , Grigoriou Maria , Sukumaran Madhu , Wang Li-Chong , Hynes Mary , Raisman Geoffrey , Pachnis Vassilis 
Published: April 2021

ABSTRACT
RET is a member of the receptor tyrosine kinase (RTK) superfamily, which can transduce signalling by glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) in cultured cells. In order to determine whether in addition to being sufficient, RET is also necessary for signalling by these growth factors, we studied the response to GDNF and NTN of primary neuronal cultures (peripheral sensory and central dopaminergic neurons) derived from wild-type and RET-deficient mice. Our experiments show that absence of a functional RET receptor abrogates the biological responses of neuronal cells to both GDNF and NTN.
Despite the established role of the RET signal transduction pathway in the development of the mammalian enteric nervous system (ENS), very little is known regarding its cellular mechanism(s) of action. Here, we have studied the effects of GDNF and NTN on cultures of neural crest (NC)-derived cells isolated from the gut of rat embryos. Our findings suggest that GDNF and NTN promote the survival of enteric neurons as well as the survival, proliferation and differentiation of multipotential ENS progenitors present in the gut of E12.5-13.5 rat embryos. However, the effects of these growth factors are stage-specific, since similar ENS cultures established from later stage embryos (E14.5-15.5), show markedly diminished response to GDNF and NTN. To examine whether the in vitro effects of RET activation reflect the in vivo function(s) of this receptor, the extent of programmed cell death was examined in the gut of wild-type and RET-deficient mouse embryos by TUNEL histochemistry. Our experiments show that a subpopulation of enteric NC undergoes apoptotic cell death specifically in the foregut of embryos lacking the RET receptor. We suggest that normal function of the RET RTK is required in vivo during early stages of ENS histogenesis for the survival of undifferentiated enteric NC and their derivatives.
Different sequence requirements for expression in erythroid and megakaryocytic cells within a regulatory element upstream of the GATA-1 gene
Authors: Vyas Paresh , McDevitt Micheal A. , Cantor Alan B. , Katz Samuel G. , Fujiwara Yuko , Orkin Stuart H. 
Published: April 2021

ABSTRACT
The lineage-restricted transcription factor GATA-1 is required for differentiation of erythroid and megakaryocytic cells. We have localized a 317 base pair cis-acting regulatory element, HS I, associated with a hematopoietic-specific DNase I hypersensitive site, which lies approx. 3.7 kilobases upstream of the murine hematopoietic-specific GATA-1 IE promoter. HS I directs high-level expression of reporter GATA-1/lacZ genes to primitive and definitive erythroid cells and megakaryocytes in transgenic mice. Comparative sequence analysis of HS I between human and mouse shows approx. 63% nucleotide identity with a more conserved core of 169 base pairs (86% identity). This core contains a GATA site separated by 10 base pairs from an E-box motif. The composite motif binds a multi-protein hematopoietic-specific transcription factor complex which includes GATA-1, SCL/tal-1, E2A, Lmo2 and Ldb-1. Point mutations of the GATA site abolishes HS I function, whereas mutation of the E-box motif still allows reporter gene expression in both lineages. Strict dependence of HS I activity on a GATA site implies that assembly of a protein complex containing a GATA-factor, presumably GATA-1 or GATA-2, is critical to activating or maintaining its function. Further dissection of the 317 base pair region demonstrates that, whereas all 317 base pairs are required for expression in megakaryocytes, only the 5′ 62 base pairs are needed for erythroid-specific reporter expression. These findings demonstrate differential lineage requirements for expression within the HS I element.
The N-terminal domain of Sxl protein disrupts Sxl autoregulation in females and promotes female-specific splicing of tra in males
Authors: Deshpande Girish , Calhoun Gretchen , Schedl Paul D. 
Published: April 2021

ABSTRACT
Sex determination in Drosophila depends upon the post-transcriptional regulatory activities of the Sex-lethal (Sxl) gene. Sxl maintains the female determined state and activates female differentiation pathways by directing the female-specific splicing of Sxl and tra pre-mRNAs. While there is compelling evidence that Sxl proteins regulate splicing by directly binding to target RNAs, previous studies indicate that the two Sxl RNA-binding domains are not in themselves sufficient for biological activity and that an intact N-terminal domain is also critical for splicing function. To further investigate the functions of the Sxl N terminus, we ectopically expressed a chimeric protein consisting of the N-terminal 99 amino acids fused to β-galactosidase. The Nβ-gal fusion protein behaves like a dominant negative, interfering with the Sxl autoregulatory feedback loop and killing females. This dominant negative activity can be attributed to the recruitment of the fusion protein into the large Sxl:Snf splicing complexes that are found in vivo and the consequent disruption of these complexes. In addition to the dominant negative activity, the Nβ-gal fusion protein has a novel gain-of-function activity in males: it promotes the female-specific processing of tra pre-mRNAs. This novel activity is discussed in light of the blockage model for the tra splicing regulation.
High Bicoid levels render the terminal system dispensable for Drosophila head development
Authors: Schaeffer Valérie , Killian Darrell , Desplan Claude , Wimmer Ernst A. 
Published: April 2021

ABSTRACT
In Drosophila, the gradient of the Bicoid (Bcd) morphogen organizes the anteroposterior axis while the ends of the embryo are patterned by the maternal terminal system. At the posterior pole, expression of terminal gap genes is mediated by the local activation of the Torso receptor tyrosine kinase (Tor). At the anterior, terminal gap genes are also activated by the Tor pathway but Bcd contributes to their activation. Here we present evidence that Tor and Bcd act independently on common target genes in an additive manner. Furthermore, we show that the terminal maternal system is not required for proper head development, since high levels of Bcd activity can functionally rescue the lack of terminal system activity at the anterior pole. This observation is consistent with a recent evolution of an anterior morphogenetic center consisting of Bcd and anterior Tor function.
Drosophila grain encodes a GATA transcription factor required for cell rearrangement during morphogenesis
Authors: Brown Stephen , Castelli-Gair Hombría James 
Published: April 2021

ABSTRACT
The genetic mechanisms controlling organ shape are largely unknown. We show that the Drosophila grain gene is required during development for shaping the adult legs and the larval posterior spiracles. Mutant legs are short and wide rather than long and thin, while the spiracles are flat instead of dome-shaped. We demonstrate that grain encodes the GATAc transcription factor. Analysis of loss- of-function mutations at the cellular level indicates that grain affects organ shape by locally controlling cell rearrangement. Ectopic grain expression causes major morphogenetic movements, resulting in the invagination of the posterior segments into the embryo. This is the first gene that has been shown to affect epithelial morphogenesis by controlling cell rearrangements, and suggests a novel function for GATA transcription factors.
The role of Xenopus dickkopf1 in prechordal plate specification and neural patterning
Authors: Kazanskaya Olga , Glinka Andrei , Niehrs Christof 
Published: April 2021

ABSTRACT
Dickkopf1 (dkk1) encodes a secreted WNT inhibitor expressed in Spemann’s organizer, which has been implicated in head induction in Xenopus. Here we have analyzed the role of dkk1 in endomesoderm specification and neural patterning by gain-and loss-of-function approaches. We find that dkk1, unlike other WNT inhibitors, is able to induce functional prechordal plate, which explains its ability to induce secondary heads with bilateral eyes. This may be due to differential WNT inhibition since dkk1, unlike frzb, inhibits Wnt3a signalling. Injection of inhibitory antiDkk1 antibodies reveals that dkk1 is not only sufficient but also required for prechordal plate formation but not for notochord formation. In the neural plate dkk1 is required for anteroposterior and dorsoventral patterning between mes-and telencephalon, where dkk1 promotes anterior and ventral fates. Both the requirement of anterior explants for dkk1 function and their ability to respond to dkk1 terminate at late gastrula stage. Xenopus embryos posteriorized with bFGF, BMP4 and Smads are rescued by dkk1. dkk1 does not interfere with the ability of bFGF to induce its immediate early target gene Xbra, indicating that its effect is indirect. In contrast, there is cross-talk between BMP and WNT signalling, since induction of BMP target genes is sensitive to WNT inhibitors until the early gastrula stage. Embryos treated with retinoic acid (RA) are not rescued by dkk1 and RA affects the central nervous system (CNS) more posterior than dkk1, suggesting that WNTs and retinoids may act to pattern anterior and posterior CNS, respectively, during gastrulation.
BMP and FGF regulate the development of EGF-responsive neural progenitor cells
Authors: Lillien Laura , Raphael Heather 
Published: April 2021

ABSTRACT
Temporal changes in progenitor cell responses to extrinsic signals play an important role in development, but little is known about the mechanisms that determine how these changes occur. In the rodent CNS, expression of epidermal growth factor receptors (EGFRs) increases during embryonic development, conferring mitotic responsiveness to EGF among multipotent stem cells. Here we show that cell-cell signaling controls this change. Whereas EGF-responsive stem cells develop on schedule in explant and aggregate cultures of embryonic cortex, co-culture with younger cortical cells delays their development. Exogenous BMP4 mimics the effect of younger cells, reversibly inhibiting changes in EGFR expression and responsiveness. Moreover, blocking endogenous BMP receptors in progenitors with a virus transducing dnBMPR1B accelerates changes in EGFR signaling. This involves a non-cell-autonomous mechanism, suggesting that BMP negatively regulates signal(s) that promote the development of EGF-responsive stem cells. FGF2 is a good candidate for such a signal, as we find that it antagonizes the inhibitory effects of younger cortical cells and exogenous BMP4. These findings suggest that a balance between antagonistic extrinsic signals regulates temporal changes in an intrinsic property of neural progenitor cells.
The WNT antagonist cSFRP2 modulates programmed cell death in the developing hindbrain
Authors: Ellies Debra L. , Church Vicki , Francis-West Philippa , Lumsden Andrew 
Published: April 2021

ABSTRACT
In the avian hindbrain, the loss of premigratory neural crest cells from rhombomeres 3 and 5 (r3, r5) through programmed cell death contributes to the patterning of emigrant crest cells into three discrete streams. Programmed cell death is induced by the upregulation of Bmp4 and Msx2 in r3 and r5. We show that cSFRP2, a WNT antagonist, is expressed in the even-numbered rhombomeres and that over-expression of cSfrp2 inhibits Bmp4 expression in r3 and r5, preventing programmed cell death. By contrast, depleting cSFRP2 function in r4 results in elevated levels of Msx2 expression and ectopic programmed cell death, as does overexpression of Wnt1. We propose that programmed cell death in the rhombencephalic neural crest is modulated by pre-patterned cSfrp2 expression and a WNT-BMP signalling loop.
Control of the migratory pathway of facial branchiomotor neurones
Authors: Garel Sonia , Garcia-Dominguez Mario , Charnay Patrick 
Published: April 2021

ABSTRACT
Facial branchiomotor (fbm) neurones undergo a complex migration in the segmented mouse hindbrain. They are born in the basal plate of rhombomere (r) 4, migrate caudally through r5, and then dorsally and radially in r6. To study how migrating cells adapt to their changing environment and control their pathway, we have analysed this stereotyped migration in wild-type and mutant backgrounds. We show that during their migration, fbm neurones regulate the expression of genes encoding the cell membrane proteins TAG-1, Ret and cadherin 8. Specific combinations of these markers are associated with each migratory phase in r4, r5 and r6. In Krox20 and kreisler mutant mouse embryos, both of which lack r5, fbm neurones migrate dorsally into the anteriorly positioned r6 and adopt an r6-specific expression pattern. In embryos deficient for Ebf1, a gene normally expressed in fbm neurones, part of the fbm neurones migrate dorsally within r5. Accordingly, fbm neurones prematurely express a combination of markers characteristic of an r6 location. These data suggest that fbm neurones adapt to their changing environment by switching on and off specific genes, and that Ebf1 is involved in the control of these responses. In addition, they establish a close correlation between the expression pattern of fbm neurones and their migratory behaviour, suggesting that modifications in gene expression participate in the selection of the local migratory pathway.
Proximal-distal leg development in Drosophila requires the apterous gene and the Lim1 homologue dlim1
Authors: Pueyo José I. , Galindo Máximo I. , Bishop Sarah A. , Couso Juan P. 
Published: April 2021

ABSTRACT
Proximal-distal leg development in Drosophila involves a battery of genes expressed and required in specific proximal-distal (PD) domains of the appendage. Here we report the characterisation of a new gene of this type, dlim1, a member of the Lhx family of genes whose proteins contain two Lim domains and a homeodomain. We show that the Lhx gene apterous (ap) is also required for PD leg development, and we study the functional interactions between ap, dlim1 and other PD genes during leg development. Our results show that a regulatory network formed by ap and dlim1 plus the homeobox genes aristaless and Bar specifies distal leg cell fates in Drosophila.
Opposing effects of bone morphogenetic proteins on neuron production and survival in the olfactory receptor neuron lineage
Authors: Shou Jianyong , Murray Richard C. , Rim Peter C. , Calof Anne L. 
Published: April 2021

ABSTRACT
In olfactory epithelium (OE) cultures, bone morphogenetic proteins (BMPs) can strongly inhibit neurogenesis. Here we provide evidence that BMPs also promote, and indeed are required, for OE neurogenesis. Addition of the BMP antagonist noggin inhibited neurogenesis in OE-stromal cell co-cultures. Bmp2, Bmp4 and Bmp7 were expressed by OE stroma, and low concentrations of BMP4 (below the threshold for inhibition of neurogenesis) stimulated neurogenesis; BMP7 did not exhibit a stimulatory effect at any concentration tested. Stromal cell conditioned medium also stimulated neurogenesis; part of this effect was due to the presence within it of a noggin-binding factor or factors. Studies of the pro-neurogenic effect of BMP4 indicated that it did not increase progenitor cell proliferation, but rather promoted survival of newly generated olfactory receptor neurons. These findings indicate that BMPs exert both positive and negative effects on neurogenesis, depending on ligand identity, ligand concentration and the particular cell in the lineage that is responding. In addition, they reveal the presence of a factor or factors, produced by OE stroma, that can synergize with BMP4 to stimulate OE neurogenesis.
DRacGAP, a novel Drosophila gene, inhibits EGFR/Ras signalling in the developing imaginal wing disc
Authors: Sotillos Sol , Campuzano Sonsoles 
Published: April 2021

ABSTRACT
We have identified a novel Drosophila gene, DRacGAP, which behaves as a negative regulator of Rho-family GTPases DRac1 and DCdc42. Reduced function of DRacGAP or increased expression of DRac1 in the wing imaginal disc cause similar effects on vein and sensory organ development and cell proliferation. These effects result from enhanced activity of the EGFR/Ras signalling pathway. We find that in the wing disc, DRac1 enhances EGFR/Ras-dependent activation of MAP Kinase in the prospective veins. Interestingly, DRacGAP expression is negatively regulated by the EGFR/Ras pathway in these regions. During vein formation, local DRacGAP repression would ensure maximal activity of Rac and, in turn, of Ras pathways in vein territories. Additionally, maximal expression of DRacGAP at the vein/intervein boundaries would help to refine the width of the veins. Hence, control of DRacGAP expression by the EGFR/Ras pathway is a previously undescribed feedback mechanism modulating the intensity and/or duration of its signalling during Drosophila development.
Regulation of the UNC-5 netrin receptor initiates the first reorientation of migrating distal tip cells in Caenorhabditis elegans
Authors: Su Ming-Wan , Merz David C. , Killeen Marie T. , Zhou Youwen , Zheng Hong , Kramer James M. , Hedgecock Edward M. , Culotti Joseph G. 
Published: April 2021

ABSTRACT
Cell migrations play a critical role in animal development and organogenesis. Here, we describe a mechanism by which the migration behaviour of a particular cell type is regulated temporally and coordinated with over-all development of the organism. The hermaphrodite distal tip cells (DTCs) of Caenorhabditis elegans migrate along the body wall in three sequential phases distinguished by the orientation of their movements, which alternate between the anteroposterior and dorsoventral axes. The ventral-to-dorsal second migration phase requires the UNC-6 netrin guidance cue and its receptors UNC-5 and UNC-40, as well as additional, UNC-6-independent guidance systems. We provide evidence that the transcriptional upregulation of unc-5 in the DTCs is coincident with the initiation of the second migration phase, and that premature UNC-5 expression in these cells induces precocious turning in an UNC-6-dependent manner. The DAF-12 steroid hormone receptor, which regulates developmental stage transitions in C. elegans, is required for initiating the first DTC turn and for coincident unc-5 upregulation. We also present evidence for the existence of a mechanism that opposes or inhibits UNC-5 function during the longitudinal first migration phase and for a mechanism that facilitates UNC-5 function during turning. The facilitating mechanism presumably does not involve transcriptional regulation of unc-5 but may represent an inhibition of the phase 1 mechanism that opposes or inhibits UNC-5. These results, therefore, reveal the existence of two mechanisms that regulate the UNC-5 receptor that are critical for responsiveness to the UNC-6 netrin guidance cue and for linking the directional guidance of migrating distal tip cells to developmental stage advancements.