bluuebunny/crossref_metadata_2025_split huggingface dataset:
A tissue-specific knock-out strategy reveals that lin-26 is required for the formation of the somatic gonad epithelium in Caenorhabditis elegans
Authors: Boer Bart G. W. den , Sookhareea Satish , Dufourcq Pascale , Labouesse Michel 
Published: April 2021

ABSTRACT
The Caenorhabditis elegans LIN-26 protein is required to specify and/or maintain the fates of all non-neuronal ectodermal cells. Here we show that lin-26 is expressed until the somatic gonad primordium stage in all cells of the somatic gonad, except in distal tip cells, and later in all uterine cells. To determine if lin-26 functions in the somatic gonad, we have generated gonad-specific lin-26 alleles obtained by integration of lin-26 promoter deletion derivatives into a lin-26 null mutant background. In this way, we rescued the lethal phenotype imparted by lin-26 null mutations and uncovered a highly penetrant sterile phenotype. Specifically, the strongest of these new alleles was characterized by the absence of lin-26 expression in the somatic gonad, the presence of endomitotic oocytes, decreased germline proliferation, a protruding vulva and a less penetrant absence of gonad arms. Lineage analysis of mutant somatic gonads and examination of several markers expressed in the spermatheca, sheath cells, distal tip cells and the uterus, suggest that LIN-26 is required in sheath, spermatheca and uterine precursors, and in uterine cells. We conclude that lin-26 performs a similar function in the non-neuronal ectoderm and the somatic gonad, a mesoderm derivative, and we speculate that lin-26 is required to express epithelial characteristics.
A conserved retinoic acid responsive element in the murine Hoxb-1 gene is required for expression in the developing gut
Authors: Huang Danyang , Chen Siming W. , Langston Alexander W. , Gudas Lorraine J. 
Published: April 2021

ABSTRACT
The murine Hoxb-1 gene contains a homeobox sequence and is expressed in a spatiotemporal specific pattern in neuroectoderm, mesoderm and gut endoderm during development. We previously identified a conserved retinoic acid (RA)-inducible enhancer, named the RAIDR5, which contains a DR5 RARE; this RAIDR5 enhancer is located 3′ of the Hoxb-1-coding region in both the mouse and chick. In the F9 murine teratocarcinoma cell line, this DR5 RARE is required for the RA response of the Hoxb-1 gene, suggesting a functional role of the DR5 RARE in Hoxb-1 gene expression during embryogenesis. From the analysis of Hoxb-1/lacZ reporter genes in transgenic mice, we have shown that a wild-type (WT) transgene with 15 kb of Hoxb-1 genomic DNA, including this Hoxb-1 3′ RAIDR5, is expressed in the same tissues and at the same times as the endogenous Hoxb-1 gene. However, a transgene construct with point mutations in the DR5 RARE (DR5mu) was not expressed in the developing foregut, which gives rise to organs such as the esophagus, lung, stomach, liver and pancreas. Like the wild-type transgene, this DR5 RARE mutated transgene was expressed in rhombomere 4 in 9.5 day postcoitum (d.p.c.) embryos. Similarly, transgene staining in the foregut of animals carrying a deletion of the entire Hox-b1 RAIDR5 enhancer (3′-del) was greatly reduced relative to that seen with the WT transgene. We also demonstrated that expression of the WT transgene in the gut increases in response to exogenous RA, resulting in anterior expansion of the expression in the gut. These observations that the Hoxb-1 gene is expressed in the developing gut and that this expression is regulated through a DR5 RARE strongly suggest a role for Hoxb-1 in the anteroposterior axis patterning of the gut and a critical role for endogenous retinoids in early gut development.
Parent-of-origin effects on seed development in Arabidopsis thaliana
Authors: Scott Rod J. , Spielman Melissa , Bailey John , Dickinson Hugh G. 
Published: April 2021

ABSTRACT
Many flowering plants are polyploid, but crosses between individuals of different ploidies produce seeds that develop abnormally and usually abort. Often, seeds from interploidy crosses develop differently depending on whether the mother or father contributes more chromosome sets, suggesting that maternal and paternal genomes are not functionally equivalent. Here we present the first cytological investigation of seed development following interploidy crosses in Arabidopsis thaliana. We find that crosses between diploid and tetraploid plants in either direction, resulting in double the normal dose of maternal or paternal genomes in the seed, produce viable seeds containing triploid embryos. However, development of the seed and in particular the endosperm is abnormal, with maternal and paternal genomic excess producing complementary phenotypes. A double dose of maternal genomes with respect to paternal contribution inhibits endosperm development and ultimately produces a smaller embryo. In contrast, a double dose of paternal genomes promotes growth of the endosperm and embryo. Reciprocal crosses between diploids and hexaploids, resulting in a triple dose of maternal or paternal genomes, produce seeds that begin development with similar but more extreme phenotypes than those with a double dose, but these invariably abort. One explanation of our observations is that seeds with maternal or paternal excess contain different doses of maternally or paternally expressed imprinted loci affecting endosperm development.
Tetraploid embryos rescue embryonic lethality caused by an additional maternally inherited X chromosome in the mouse
Authors: Goto Yuji , Takagi Nobuo 
Published: April 2021

ABSTRACT
Mouse embryos with an additional maternally inherited X chromosome, i.e., disomic for XM (DsXM), cease to grow early in development and have a deficient extraembryonic region. We hypothesized that the underdeveloped extraembryonic region is attributed to two copies of XM that escape inactivation due to maternal imprinting. To examine the validity of this hypothesis and throw more light on the significance of X chromosome dosage on cell differentiation, we generated DsXM(XMXMXP and XMXMY) embryos at a high frequency taking advantage of the elevated incidence of X chromosome nondisjunction in female mice heterozygous for two Robertsonian X-autosome translocations, Rb(X.2)2Ad and Rb(X.9)6H. Although two XM chromosomes seem to remain active in both trophectoderm and primitive endoderm, detailed histological examination showed that the polar trophectoderm derivatives (ectoplacental cone and extraembryonic ectoderm) are severely affected, but the primitive endoderm derivatives (visceral and parietal endoderm) are relatively unaffected. Successful rescue of DsXM embryos by aggregation with tetraploid embryos show that X chromosome inactivation occurred normally leaving one X active in epiblast derivatives. Thus, two copies of active XM chromosome in cells of the polar trophectoderm cell lineage seem to be the main cause of early lethality shown by DsXM embryos as a result of failure in formation of ectoplacental cone and extraembryonic ectoderm.
Zebrafish paraxial protocadherin is a downstream target of spadetail involved in morphogenesis of gastrula mesoderm
Authors: Yamamoto Akihito , Amacher Sharon L. , Kim Sung-Hyun , Geissert Douglas , Kimmel Charles B. , Robertis E. M. De 
Published: April 2021

ABSTRACT
Zebrafish paraxial protocadherin (papc) encodes a transmembrane cell adhesion molecule (PAPC) expressed in trunk mesoderm undergoing morphogenesis. Microinjection studies with a dominant-negative secreted construct suggest that papc is required for proper dorsal convergence movements during gastrulation. Genetic studies show that papc is a close downstream target of spadetail, gene encoding a transcription factor required for mesodermal morphogenetic movements. Further, we show that the floating head homeobox gene is required in axial mesoderm to repress the expression of both spadetail and papc, promoting notochord and blocking differentiation of paraxial mesoderm. The PAPC structural cell-surface protein may provide a link between regulatory transcription factors and the actual cell biological behaviors that execute morphogenesis during gastrulation.
EGFR signaling is required for the differentiation and maintenance of neural progenitors along the dorsal midline of the Drosophila embryonic head
Authors: Dumstrei Karin , Nassif Claude , Abboud Gebran , Aryai Arezou , Aryai Arman , Hartenstein Volker 
Published: April 2021

ABSTRACT
EGFR signaling has been shown in recent years to be involved in the determination, differentiation and maintenance of neural and epidermal cells of the ventral midline (mesectoderm and ventromedial ectoderm). Localized activation of the TGFα homolog Spitz (Spi) in the mesectoderm is achieved by the products of the genes rhomboid and Star. Spi binds to its receptor, the Drosophila epidermal growth factor receptor homolog (Egfr), and triggers the Ras pathway which is needed for the survival and differentiation of ventral midline cells. The results reported here indicate that EGFR signaling is also required in a narrow medial domain of the head ectoderm (called ‘head midline’ in the following) that includes the anlagen of the medial brain, the visual system (optic lobe, larval eye) and the stomatogastric nervous system (SNS). We document that genes involved in EGFR signaling are expressed in the head midline. Loss of EGFR signaling results in an almost total absence of optic lobe and larval eye, as well as severe reduction of SNS and medial brain. The cellular mechanism by which this phenotype arises is a failure of neurectodermal cells to differentiate combined with apoptotic cell death. Overactivity of EGFR signaling, as achieved by heat-shock-driven activation of a wild-type rhomboid (rho) construct, or by loss of function of argos (aos) or yan, results in an hyperplasia and deformity of the head midline structures. We show that, beside their requirement for EGFR signaling, head and ventral midline structures share several morphogenetic and molecular properties.
The Drosophila Polycomb Group proteins ESC and E(Z) bind directly to each other and co-localize at multiple chromosomal sites
Authors: Tie Feng , Furuyama Takehito , Harte Peter J. 
Published: April 2021

ABSTRACT
The Polycomb Group gene esc encodes an evolutionarily conserved protein required for transcriptional silencing of the homeotic genes. Unlike other Polycomb Group genes, esc is expressed and apparently required only during early embryogenesis, suggesting it is required for the initial establishment of silencing but not for its subsequent maintenance. We present evidence that the ESC protein interacts directly with E(Z), another Polycomb Group protein required for silencing of the homeotic genes. We show that the most highly conserved region of ESC, containing seven WD motifs that are predicted to fold into a β-propeller structure, mediate its binding to a conserved N-terminal region of E(Z). Mutations in the WD region that perturb ESC silencing function in vivo also perturb binding to E(Z) in vitro. The entire WD region forms a trypsin-resistant structure, like known β-propeller domains, and mutations that would affect the predicted ESC β-propeller perturb its trypsin-resistance, while a putative structure-conserving mutation does not. We show by co-immunoprecipitation that ESC and E(Z) are directly associated in vivo and that they also co-localize at many chromosomal binding sites. Since E(Z) is required for binding of other Polycomb Group proteins to chromosomes, these results suggest that formation of an E(Z):ESC complex at Polycomb Response Elements may be an essential prerequisite for the establishment of silencing.
Development of several epidermal cell types can be specified by the same MYB-related plant transcription factor
Authors: Glover Beverley J. , Perez-Rodriguez Maria , Martin Cathie 
Published: April 2021

ABSTRACT
A MYB-related transcription factor (MIXTA) that controls development of conical cell form is expressed only in the inner epidermis of Antirrhinum petals. Expression of this gene throughout transgenic tobacco plants leads to excess numbers of multicellular trichomes on leaves and floral organs as well as the novel production of conical cells on leaves. These data indicate that conical cells and trichomes are produced by a common developmental pathway. The timing of MIXTA expression suggests that the choice between the cell types depends on the competence for cell division at the time at which the controlling gene is expressed. Duplication of genes and their association with different cis-regulatory regions may therefore result in the specification of novel plant cell types.
Lozenge is expressed in pluripotent precursor cells and patterns multiple cell types in the Drosophila eye through the control of cell-specific transcription factors
Authors: Flores Gail V. , Daga Andrea , Kalhor Hamid R. , Banerjee Utpal 
Published: April 2021

ABSTRACT
In the developing Drosophila eye, individual cell fates are specified when general signaling mechanisms are interpreted in the context of cell-specific transcription factors. Lozenge, a Runt/AML1/CBFA1-like transcription factor, determines the fates of a number of neuronal and non-neuronal cells by regulating the expression of multiple fate-determining transcription factors. The Lozenge protein is expressed in the nuclei of the cells that it patterns and also in their undifferentiated precursors. An enhancer element located within the second intron of the lozenge gene is responsible for its eye-specific expression. Lozenge is not itself a cell-specific transcription factor, rather it prepatterns the eye disc by positioning cell-specific factors in their appropriate locations.
Signals transmitted along retinal axons in Drosophila: Hedgehog signal reception and the cell circuitry of lamina cartridge assembly
Authors: Huang Zhen , Kunes Samuel 
Published: April 2021

ABSTRACT
The arrival of retinal axons in the brain of Drosophila triggers the assembly of glial and neuronal precursors into a ‘neurocrystalline’ array of lamina synaptic ‘cartridges’. Hedgehog, a secreted protein, is an inductive signal delivered by retinal axons for the initial steps of lamina differentiation. In the development of many tissues, Hedgehog acts in a signal relay cascade via the induction of secondary secreted factors. Here we show that lamina neuronal precursors respond directly to Hedgehog signal reception by entering S-phase, a step that is controlled by the Hedgehog-dependent transcriptional regulator Cubitus interruptus. The terminal differentiation of neuronal precursors and the migration and differentiation of glia appear to be controlled by other retinal axon-mediated signals. Thus retinal axons impose a program of developmental events on their postsynaptic field utilizing distinct signals for different precursor populations.
Two distinct mechanisms for differential positioning of gene expression borders involving the Drosophila gap protein giant
Authors: Wu Xuelin , Vakani Rajesh , Small Stephen 
Published: April 2021

ABSTRACT
We have combined genetic experiments and a targeted misexpression approach to examine the role of the gap gene giant (gt) in patterning anterior regions of the Drosophila embryo. Our results suggest that gt functions in the repression of three target genes, the gap genes Krüppel (Kr) and hunchback (hb), and the pair-rule gene even-skipped (eve). The anterior border of Kr, which lies 4-5 nucleus diameters posterior to nuclei that express gt mRNA, is set by a threshold repression mechanism involving very low levels of gt protein. In contrast, gt activity is required, but not sufficient for formation of the anterior border of eve stripe 2, which lies adjacent to nuclei that express gt mRNA. We propose that gt’s role in forming this border is to potentiate repressive interaction(s) mediated by other factor(s) that are also localized to anterior regions of the early embryo. Finally, gt is required for repression of zygotic hb expression in more anterior regions of the embryo. The differential responses of these target genes to gt repression are critical for the correct positioning and maintenance of segmentation stripes, and normal anterior development.
The Arabidopsis thaliana gametophytic mutation gemini pollen1 disrupts microspore polarity, division asymmetry and pollen cell fate
Authors: Park Soon Ki , Howden Ross , Twell David 
Published: April 2021

ABSTRACT
Pollen development and male gametogenesis are critically dependent upon cell polarization leading to a highly asymmetric cell division termed pollen mitosis I. A mutational approach was adopted in Arabidopsis thaliana to identify genes involved these processes. Four independent gemini pollen mutants were isolated which produce divided or twin-celled pollen. The gemini pollen1 mutant was characterized in detail and shown to act gametophytically resulting in reduced transmission through both sexes. gemini pollen1 showed an incompletely penetrant phenotype resulting in equal, unequal and partial divisions at pollen mitosis I. The division planes in gemini pollen1 were shown to be aligned with the polar axis (as in wild type) and evidence was obtained for incomplete nuclear migration, which could account for altered division symmetry. gemini pollen1 also showed division phenotypes consistent with spatial uncoupling of karyokinesis and cytokinesis suggesting that GEMINI POLLEN1 may be required for the localization of phragmoplast activity. Cell fate studies showed that in both equal and unequal divisions a vegetative cell marker gene was activated in both daughter cells. Daughter cells with a range of intermediate or hybrid vegetative/ generative cell fates suggests that cell fate is quantitatively related to cell size. The potential mode of action of GEMINI POLLEN1 and its effects on cell fate are discussed in relation to proposed models of microspore polarity and cell fate determination.
Prx1 and Prx2 in skeletogenesis: roles in the craniofacial region, inner ear and limbs
Authors: ten Berge Derk , Brouwer Antje , Korving Jeroen , Martin James F. , Meijlink Frits 
Published: April 2021

ABSTRACT
Prx1 and Prx2 are closely related paired-class homeobox genes that are expressed in very similar patterns predominantly in mesenchyme. Prx1 loss-of-function mutants show skeletal defects in skull, limbs and vertebral column (Martin, J. F., Bradley, A. and Olson, E. N. (1995) Genes Dev. 9, 1237-1249). We report here that mice in which Prx2 is inactivated by a lacZ insertion had no skeletal defects, whereas Prx1/Prx2 double mutants showed many novel abnormalities in addition to an aggravation of the Prx1 single mutant phenotype. We found defects in external, middle and inner ear, reduction or loss of skull bones, a reduced and sometimes cleft mandible, and limb abnormalities including postaxial polydactyly and bent zeugopods. A single, or no incisor was present in the lower jaw, and ectopic expression of Fgf8 and Pax9 was found medially in the mandibular arch. A novel method to detect β-galactosidase activity in hydroxyethylmethacrylate sections allowed detailed analysis of Prx2 expression in affected structures. Our results suggest a role for Prx genes in mediating epitheliomesenchymal interactions in inner ear and lower jaw. In addition, Prx1 and Prx2 are involved in interactions between perichondrium and chondrocytes that regulate their proliferation or differentiation in the bones of the zeugopods.
The Pristionchus HOX gene Ppa-lin-39 inhibits programmed cell death to specify the vulva equivalence group and is not required during vulval induction
Authors: Sommer Ralf J. , Eizinger Andreas , Lee Kwang-Zin , Jungblut Benno , Bubeck Anja , Schlak Isabel 
Published: April 2021

ABSTRACT
In the two nematode species Caenorhabditis elegans and Pristionchus pacificus the vulva equivalence group in the central body region is specified by the Hox gene lin-39. C. elegans lin-39 mutants are vulvaless and the vulval precursor cells fuse with the surrounding hypodermis, whereas in P. pacificus lin-39 mutants the vulval precursor cells die by apoptosis. Mechanistically, LIN-39 might inhibit non-vulval fate (cell fusion in C. elegans, apoptosis in P. pacificus), promote vulval fate or do both. To study the mechanism of lin-39 function, we isolated P. pacificus cell death mutants and identified mutations in ced-3. Surprisingly, P. pacificus ced-3; lin-39 double mutants form a functional vulva in the absence of LIN-39 activity. Thus, in P. pacificus lin-39 specifies the vulva equivalence group by inhibiting programmed cell death. Furthermore, these data reveal an important difference in a later function of lin-39 between the two species. In C. elegans, LIN-39 specifies vulval cell fates in response to inductive RAS signaling, and in P. pacificus LIN-39 is not required for vulval induction. Thus, the comparative analysis indicates that lin-39 has distinct functions in both species although the gene is acting in a homologous developmental system.
A Xenopus DAZ-like gene encodes an RNA component of germ plasm and is a functional homologue of Drosophila boule
Authors: Houston Douglas W. , Zhang Jian , Maines Jean Z. , Wasserman Steven A. , King Mary Lou 
Published: April 2021

ABSTRACT
We have identified a localized RNA component of Xenopus germ plasm. This RNA, Xdazl (Xenopus DAZ-like), encodes a protein homologous to human DAZ (Deleted in Azoospermia), vertebrate DAZL and Drosophila Boule proteins. Human males deficient in DAZ have few or no sperm and boule mutant flies exhibit complete azoospermia and male sterility. Xdazl RNA was detected in the mitochondrial cloud and vegetal cortex of oocytes. In early embryos, the RNA was localized exclusively in the germ plasm. Consistent with other organisms, Xdazl RNA was also expressed in the spermatogonia and spermatocytes of frog testis. Proteins in the DAZ-family contain a conserved RNP domain implying an RNA-binding function. We have shown that Xdazl can function in vitro as an RNA-binding protein. To determine if the function of Xdazl in spermatogenesis was conserved, we introduced the Xdazl cDNA into boule flies. This resulted in rescue of the boule meiotic entry phenotype, including formation of spindles, phosphorylation of histone H3 and completion of meiotic cell division. Overall, these results suggest that Xdazl may be important for primordial germ cell specification in the early embryo and may play a role analogous to Boule in promoting meiotic cell division.
Sequential activation of the EGF receptor pathway during Drosophila oogenesis establishes the dorsoventral axis
Authors: Sapir Amir , Schweitzer Ronen , Shilo Ben-Zion 
Published: April 2021

ABSTRACT
Previous work has demonstrated a role for the Drosophila EGF receptor (Torpedo/DER) and its ligand, Gurken, in the determination of anterioposterior and dorsoventral axes of the follicle cells and oocyte. The roles of DER in establishing the polarity of the follicle cells were examined further, by following the expression of DER-target genes. One class of genes (e.g. kekon) is induced by the DER pathway at all stages. Broad expression of kekon at the stage in which the follicle cells migrate posteriorly over the oocyte, demonstrates the capacity of the pathway to pattern all follicle cells except the ventral-most rows. This may provide the spatial coordinates for the ventral-most follicle cell fates. A second group of target genes (e.g. rhomboid (rho)) is induced only at later stages of oogenesis, and may require additional inputs by signals emanating from the anterior, stretch follicle cells. The function of Rho was analyzed by ectopic expression in the stretch follicle cells, and shown to induce a non-autonomous dorsalizing activity that is independent of Gurken. Rho thus appears to be involved in processing a DER ligand in the follicle cells, to pattern the egg chamber and allow persistent activation of the DER pathway during formation of the dorsal appendages.