bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transcriptional regulation of Notch and Delta: requirement for neuroblast segregation in Drosophila
Authors: Seugnet Laurent , Simpson Pat , Haenlin Marc 
Published: April 2021

ABSTRACT
Segregation of a single neural precursor from each proneural cluster in Drosophila relies on Notch-mediated lateral signalling. Studies concerning the spacing of precursors for the microchaetes of the peripheral nervous system suggested the existence of a regulatory loop between Notch and its ligand Delta within each cell that is under transcriptional control. Activation of Notch leads to repression of the achaete-scute genes which themselves regulate transcription of Delta, perhaps directly. Here we have tested a requirement for transcriptional regulation of Notch and/or Delta during neuroblast segregation in embryos, by providing Notch and Delta ubiquitously at uniform levels. Neuroblast segregation occurs normally under conditions of uniform Notch expression. Under conditions of uniform Delta expression, a single neuroblast segregates from each proneural group in 80% of the cases, more than one in the remaining 20%. Thus transcriptional regulation of Delta is largely dispensable. We discuss the possibility that segregation of single precursors in the central nervous system may rely on a heterogeneous distribution of neural potential between different cells of the proneural group. Notch signalling would enable all cells to mutually repress each other and only a cell with an elevated neural potential could overcome this repression.
Flk-1 expression defines a population of early embryonic hematopoietic precursors
Authors: Kabrun Neil , Bühring Hans-Jörg , Choi Kyunghee , Ullrich Axel , Risau Werner , Keller Gordon 
Published: April 2021

Summary
We have investigated the expression pattern of the Flk-1 receptor tyrosine kinase in mouse embryonic and fetal hematopoietic tissues as well as on hematopoietic precursor cells derived from these tissues. RNA analysis indicated that flk-1 was expressed in the yolk sac at day 10 of gestation, in the whole embryo at day 10 and 12 of gestation, in the liver throughout fetal life and in embryoid bodies (EBs) generated from ES cells differentiated in culture. Flk-1 message was also detected in erythroid and macrophage colonies generated from precursors of yolk sac, fetal liver, adult marrow and eB origin. Using an antibody directed against the extracellular portion of the molecule we have found that up to 50% of cells from EBs differentiated for 4 days express Flk-1. Following the development of this early Flk-1+ population the number of receptor-positive cells declines progressively to represent less than 5% of the EBs by day 12 of differentiation. Kinetic analysis revealed that the establishment of the EB Flk-1+ population precedes the development of cells which express CD34, Ly6A (Sca-1) and AA4.1. Cell sorting experiments demonstrated that all day-4 EB-derived hematopoietic precursors are Flk-1+ whereas greater than 95% of those found within the day-12 EBs are Flk-1−, suggesting that the precursor population which expresses this receptor represents an early but transient wave of hematopoietic development. Analysis of yolk sac and whole embryos at day 8.5 of gestation revealed a small but distinct Flk-1+ population that contained hematopoietic precursors. Day-12.5 fetal liver contained few Flk-1+ cells that showed little hematopoietic potential. Together these findings indicate that Flk-1 is expressed on an early population of hematopoietic precursors that may represent the onset of embryonic hematopoiesis.
Cell movements, neuronal organisation and gene expression in hindbrains lacking morphological boundaries
Authors: Nittenberg Ronald , Patel Ketan , Joshi Yogish , Krumlauf Robb , Wilkinson David G. , Brickell Paul M. , Tickle Cheryll , Clarke Jonathan D. W. 
Published: April 2021

ABSTRACT
Rhombomeres are segmental units of the hindbrain that are separated from each other by a specialised zone of boundary cells. Retinoic acid application to a recently segmented hindbrain leads to disappearance of posterior rhombomere boundaries. Boundary loss is preceded by changes in segmental expression of Krox-20 and Cek-8 and followed by alterations in Hox gene expression. The characteristic morphology of boundary cells, their expression of follistatin and the periodic accumulation of axons normally associated with boundaries are all lost. In the absence of boundaries, we detect no change in anteroposterior dispersal of precursor cells and, in most cases, no substantial cell mixing between former rhombomeric units. This is consistent with the idea that lineage restriction can be maintained by processes other than a mechanical barrier composed of boundary cells. Much of the early organisation of the motor nuclei appears normal despite the loss of boundaries and altered Hox expression.
Bmp-4 acts as a morphogen in dorsoventral mesoderm patterning in Xenopus
Authors: Dosch Roland , Gawantka Volker , Delius Hajo , Blumenstock Claudia , Niehrs Christof 
Published: April 2021

ABSTRACT
The marginal zone is a ring of tissue that gives rise to a characteristic dorsoventral pattern of mesoderm in amphibian embryos. Bmp-4 is thought to play an important role in specifying ventral mesodermal fate. Here we show (1)that different doses of Bmp-4 are sufficient to pattern four distinct mesodermal cell types and to pattern gene expression in the early gastrula marginal zone into three domains, (2) that there is a graded requirement for a Bmp signal in mesodermal patterning, and (3) that Bmp-4 has long-range activity which can become graded in the marginal zone by the antagonizing action of noggin. The results argue that Bmp-4 acts as a morphogen in dorsoventral patterning of mesoderm.
The Pax protein Noi is required for commissural axon pathway formation in the rostral forebrain
Authors: Macdonald Rachel , Scholes John , Strähle Uwe , Brennan Caroline , Holder Nigel , Brand Michael , Wilson Stephen W. 
Published: April 2021

ABSTRACT
No-isthmus (Noi) is a member of the zebrafish Pax family of transcriptional regulators that is expressed in restricted domains of the developing CNS. In the developing eye and optic nerve, the Noi + cells are primitive glial cells that line the choroid fissure and optic stalk/nerve to its junction with the optic tract. This pattern of Noi expression is retained in the adult, defining the optic nerve astroglia, which wrap the left and right nerves separately at the midline, thus forming the bodily crossed optic chiasm found in fish. In embryos carrying mutations in the noi gene, the choroid fissure fails to close, glial cells of the optic nerve fail to dif-ferentiate and optic axons exhibit abnormal trajectories exiting the eye and at the midline of the diencephalon. Optic axons select inappropriate pathways into the con-tralateral optic nerve, rostrally towards the anterior com-missure and along the ipsilateral optic tract. Noi+ cells also border the pathway of axons in the postoptic commissure, which is located adjacent to the optic chiasm. These postoptic commissural axons are defasciculated and also exhibit pathfinding defects in noi− embryos. These results indicate that Noi is required in cells that line the pathways taken by optic and non-optic commissural axons for guidance across the midline of the diencephalon. We find that expression of two members of the Netrin family of axon guidance molecules and the signalling protein Sonic hedgehog is disturbed in noi− embryos, whereas several members of the Eph family of receptors and ligands show no obvious alterations in expression at the diencephalic midline.
Analysis of growth factor and receptor mRNA levels during development of the rat seminal vesicle and prostate
Authors: Thomson Axel A. , Foster Barbara A. , Cunha Gerald R. 
Published: April 2021

ABSTRACT
Development of the mammalian male accessory sexual organs requires both androgens and mesenchymal/epithelial interactions. Paracrine acting factors whose expression is mesenchymal and androgen dependent have been proposed to regulate development of these organs, although the identity of these paracrine mediators is unknown. Keratinocyte growth factor (Kgf) has been shown to play an important role in the development of the mouse seminal vesicle and rat ventral prostate. Also, Kgf is expressed in mesenchymal cells and has been shown to be regulated by androgens in prostatic cells grown in vitro. Thus Kgf has been proposed as a mediator of androgen action. We have investigated the expression of Kgf mRNA during development of the rat seminal vesicle and prostate, both in vitro and in vivo. Additionally we have examined mRNAs for Kgf receptor (KgfR), transforming growth factor alpha (Tgf α), epidermal growth factor receptor (EgfR) and cytokeratin 19 (CK19). The levels of growth factor and receptor mRNAs fluctuated during androgen-regulated development; however, these changes reflected variations in the mesenchymal/epithelial ratio rather than regulation by testosterone. Expression of Kgf is mesenchymal, while KgfR is epithelial and Tgf α is predominantly epithelial. The changes in the levels of mRNAs for these factors correlated well with changes in the level of an epithelial marker, CK19, suggesting they were due to alterations in the relative abundance of tissue compartments in which they were expressed. Kgf has been shown to mimic androgen action in explant cultures of seminal vesicle and prostate. We demonstrate here that anti-androgens are able to block Kgf stimulated development, suggesting that Kgf and androgen receptor signalling pathways may interact. Taken together our data suggest that, in vivo, Kgf may interact with androgen receptor signalling but it is not a direct target of androgen action.
A novel group of pumilio mutations affects the asymmetric division of germline stem cells in the Drosophila ovary
Authors: Lin Haifan , Spradling Allan C. 
Published: April 2021

ABSTRACT
Germline stem cells play a pivotal role in gametogenesis; yet little is known about how they are formed, how they divide to self-renew, and how these processes are genetically controlled. Here we describe the self-renewing asymmetric division of germline stem cells in the Drosophila ovarian germline, as marked by the spectrosome, a cytoplasmic structure rich in membrane skeletal proteins. The ontogeny of the spectrosome marks the lineage of germline stem cells. We identified two new groups of mutations in which the divisional asymmetry is disrupted. The first, which we refer to as ovarette (ovt) mutations, was shown to correspond to a novel class of mutations in the pumilio locus. Since pumilio is known to posttranscriptionally repress the expression of target genes at earlier stages of germ cell development, our results suggest that a similar activity is needed to maintain germ line stem cells. We have also identified a second and novel gene, piwi, whose mutations abolish germline stem cell division.
Mechanisms of dorsal-ventral patterning in noggin-induced neural tissue
Authors: Knecht Anne K. , Harland Richard M. 
Published: April 2021

ABSTRACT
We have investigated mechanisms of dorsal-ventral patterning of neural tissue, using Xenopus ectoderm neuralized by noggin protein. This tissue appears to be patterned dorsoventrally; cpl-1, a gene expressed in the dorsal brain, and etr-1, a gene largely excluded from the dorsal brain, are expressed in separate territories in noggin-treated explants (Knecht, A. K., Good, P. J., Dawid, I. B. and Harland, R. M. (1995) Development 121, 1927-1936). Here we show further evidence that this pattern represents a partial dorsal-ventral organization. Additionally, we test two mechanisms that could account for this pattern: a dosedependent response to a gradient of noggin protein within the explant, and regulative cell-cell interactions. We show that noggin exhibits concentration-dependent effects, inducing cpl-1 at low doses but repressing it at high doses. Since noggin acts by antagonizing Bone Morphogenetic Protein (BMP) signaling, this result suggests that BMPs also may act in a dose-dependent manner in vivo. However, in the absence of a noggin gradient, regulative cell-cell interactions can also pattern the tissue. Such regulation is facilitated by increased motility of noggin-treated cells. Finally, the response of cells to both of these patterning mechanisms is ultimately controlled by a third process, the changing competence of the responding tissue.
Myogenin can substitute for Myf5 in promoting myogenesis but less efficiently
Authors: Wang Yukang , Jaenisch Rudolf 
Published: April 2021

ABSTRACT
The myogenic basic Helix-Loop-Helix transcription factors, including Myf5, MyoD, myogenin (myg) and MRF4, play important roles in skeletal muscle development. The phenotypes of mutant mice deficient in either gene are different, suggesting that each gene may have a unique function in vivo. We previously showed that targeting myogenin into the Myf5locus (Myf5myg-ki) rescued the rib cage truncation in the Myf5-null mutant, hence demonstrating functional redundancy between Myf5 and myogenin in skeletal morphogenesis. Here we present the results of crossing myogenin knock-in (myg-ki) mice with either MyoD-null or myogenin-null mutants. The Myf5myg-ki allele rescued early myogenesis, but Myf5(myg-ki/myg-ki);MyoD−(/−) mutant mice died immediately after birth owing to reduced muscle formation. Therefore, myogenin, expressed from the Myf5 locus, is not able to completely replace the function of Myf5 in muscle devel-opment although it is capable of determining and/or maintaining myogenic lineage. Myf5(myg-ki/myg-ki);myg−(/−) mutant mice displayed the same phenotype as myg(−/−) mutants. This indicates that the earlier expression of myogenin cannot promote myogenic terminal differentiation, which is normally initiated by the endogenous myogenin. Thus, our results are consistent with the notion that Myf5 and myogenin are functionally interchangeable in determining myogenic lineage and assuring normal rib formation. Our experiment revealed, however, that some aspects of myogenesis may be unique to a given myogenic factor and are due to either different regulatory sequences that control their temporal and spatial expression or different functional protein domains.
β3-tubulin is directly repressed by the Engrailed protein in Drosophila
Authors: Serrano Nuria , Brock Hugh W. , Maschat Florence 
Published: April 2021

ABSTRACT
In Drosophila, Engrailed is a nuclear regulatory protein with essential roles during embryonic development. Although Engrailed is a transcription factor, little progress has been achieved in identifying its target genes. We report here the identification of an effector gene, the β3-tubulin gene, as a direct target of Engrailed. The cytological location of β3-tubulin, 60C, is a strong site of Engrailed binding on polytene chromosomes. Immunostaining analysis of a transgenic line containing a P[β3-tubulin-lacZ] construct shows an additional site of Engrailed binding at the location of the transgene. Molecular analysis allowed identification of several Engrailed binding sites, both in vitro and in vivo, within the first intron of the β3-tubulin locus. Engrailed binding sites identified in vitro are active in larvae. Furthermore, expression of β3-tubulin is de-repressed in the ectoderm of engrailed mutant embryos. Repression of β3-tubulin by Engrailed is also obtained when Engrailed is ectopically expressed in embryonic mesoderm. Finally, two different sets of Engrailed binding sites are shown to be involved in the early and late regulation of β3-tubulin by Engrailed during embryogenesis.
The Drosophila G-protein-coupled receptor kinase homologue Gprk2 is required for egg morphogenesis
Authors: Schneider Lynne E. , Spradling Allan C. 
Published: April 2021

ABSTRACT
G protein signaling is a widely utilized form of extracellular communication that is mediated by a family of serpentine receptors containing seven transmembrane domains. In sensory neurons, cardiac muscle and other tissues, G protein-coupled receptors are desensitized through phosphorylation by a family of kinases, the G protein-coupled receptor kinases (GRKs). Desensitization allows a cell to decrease its response to a given signal, in the continued presence of that signal. We have identified a Drosophila mutant, gprk26936 that disrupts expression of a putative member of the GRK family, the G protein-coupled receptor kinase 2 gene (Gprk2). This mutation affects Gprk2 gene expression in the ovaries and renders mutant females sterile. The mutant eggs contain defects in several anterior eggshell structures that are produced by specific subsets of migratory follicle cells. In addition, rare eggs that become fertilized display gross defects in embryogenesis. These observations suggest that developmental signals transduced by G protein-coupled receptors are regulated by receptor phosphorylation. Based on the known functions of G protein-coupled receptor kinases, we speculate that receptor desensitization assists cells that are migrating or undergoing shape changes to respond rapidly to changing external signals.
Genetic evidence that heparin-like glycosaminoglycans are involved in wingless signaling
Authors: Binari Richard C. , Staveley Brian E. , Johnson Wayne A. , Godavarti Ranga , Sasisekharan Ram , Manoukian Armen S. 
Published: April 2021

ABSTRACT
We have identified the Drosophila UDP-glucose dehydro-genase gene as being involved in wingless signaling. Mutations in this gene, called kiwi, generate a phenotype identical to that of wingless.UDP-glucose dehydrogenase is required for the biosynthesis of UDP-glucuronate, which in turn is utilized in the biosynthesis of glycosaminoglycans. By rescuing the kiwiphenotype with both UDP-glucuronate and the glycosaminoglycan heparan sulfate, we show that kiwi function in the embryo is crucial for the production of heparan sulfate in the extracellular matrix. Further, injection of heparin degrading enzyme, heparinase (and not chondroitin, dermatan or hyaluronic acid degrading enzyme) into wild-type embryos leads to the degradation of heparin-like glycosaminoglycans and a ‘wingless-like’ cuticular phenotype. Our study thus provides the first genetic evidence for the involvement of heparin-like gly-cosaminoglycans in signal transduction.
Development of branchiomotor neurons in zebrafish
Authors: Chandrasekhar Anand , Moens Cecilia B. , Warren James T. , Kimmel Charles B. , Kuwada John Y. 
Published: April 2021

ABSTRACT
The mechanisms underlying neuronal specification and axonogenesis in the vertebrate hindbrain are poorly under-stood. To address these questions, we have employed anatomical methods and mutational analysis to character-ize the branchiomotor neurons in the zebrafish embryo. The zebrafish branchiomotor system is similar to those in the chick and mouse, except for the location of the nVII and nIX branchiomotor neurons. Developmental analyses of genes expressed by branchiomotor neurons suggest that the different location of the nVII neurons in the zebrafish may result from cell migration.
To gain insight into the mechanisms underlying the organization and axonogenesis of these neurons, we examined the development of the branchiomotor pathways in neuronal mutants. The valentinob337 mutation blocks the formation of rhombomeres 5 and 6, and severely affects the development of the nVII and nIX motor nuclei. The cyclopsb16 mutation deletes ventral midline cells in the neural tube, and leads to a severe disruption of most bran-chiomotor nuclei and axon pathways. These results demon-strate that rhombomere-specific cues and ventral midline cells play important roles in the development of the bran-chiomotor pathways.
TETRASPORE is required for male meiotic cytokinesis in Arabidopsis thaliana
Authors: Spielman Melissa , Preuss Daphne , Li Feng-Lan , Browne William E. , Scott Rod J. , Dickinson Hugh G. 
Published: April 2021

ABSTRACT
In flowering plants, male meiosis occurs in the microsporocyte to produce four microspores, each of which develops into a pollen grain. Here we describe four mutant alleles of TETRASPORE (TES), a gene essential for microsporocyte cytokinesis in Arabidopsis thaliana. Following failure of male meiotic cytokinesis intes mutants, all four microspore nuclei remain within the same cytoplasm, with some completing their developmental programmes to form functional pollen nuclei. Both of the mitotic divisions seen in normal pollen development take place in tes mutants, including the asymmetric division required for the differentiation of gametes; some tes grains perform multiple asymmetric divisions in the same cytoplasm. tes pollen shows a variety of abnormalities subsequent to the cytokinetic defect, including fusion of nuclei, formation of ectopic internal walls, and disruptions to external wall patterning. In addition, ovules fertilized by tes pollen often abort, possibly because of excess paternal genomes in the endosperm. Thus tes mutants not only reveal a gene specific to male meiosis, but aid investigation of a wide range of processes in pollen development and function.
TGFβ2 knockout mice have multiple developmental defects that are non-overlapping with other TGFβ knockout phenotypes
Authors: Sanford L. Philip , Ormsby Ilona , Groot Adriana C. Gittenberger-de , Sariola Hannu , Friedman Rick , Boivin Gregory P. , Cardell Emma Lou , Doetschman Thomas 
Published: April 2021

ABSTRACT
The growth and differentiation factor transforming growth factor-β2 (TGFβ2) is thought to play important roles in multiple developmental processes. Targeted disruption of the TGF β2 gene was undertaken to determine its essential role in vivo. TGFβ2-null mice exhibit perinatal mortality and a wide range of developmental defects for a single gene disruption. These include cardiac, lung, craniofacial, limb, spinal column, eye, inner ear and urogenital defects. The developmental processes most commonly involved in the affected tissues include epithelial-mesenchymal interac-tions, cell growth, extracellular matrix production and tissue remodeling. In addition, many affected tissues have neural crest-derived components and simulate neural crest deficiencies. There is no phenotypic overlap with TGFβ1- and TGF β3-null mice indicating numerous non-compen-sated functions between the TGFβ isoforms.
Induction of identified mesodermal cells by CNS midline progenitors in Drosophila
Authors: Lüer Karin , Urban Joachim , Klämbt Christian , Technau Gerhard M. 
Published: April 2021

ABSTRACT
The Drosophila ventral midline cells generate a discrete set of CNS lineages, required for proper patterning of the ventral ectoderm. Here we provide the first evidence that the CNS midline cells also exert inductive effects on the mesoderm. Mesodermal progenitors adjacent to the midline progenitor cells give rise to ventral somatic mucles and a pair of unique cells that come to lie dorsomedially on top of the ventral nerve cord, the so-called DM cells. Cell ablation as well as cell transplantation experiments indicate that formation of the DM cells is induced by midline progenitors in the early embryo. These results are corroborated by genetic analyses. Mutant single minded embryos lack the CNS midline as well as the DM cells. Embryos mutant for any of the spitz group genes, which primarily express defects in the midline glial cell lineages, show reduced formation of the DM cells. Conversely, directed overexpression of secreted SPITZ by some or all CNS midline cells leads to the formation of additional DM cells. Furthermore we show that DM cell development does not depend on the absolute concentration of a local inductor but appears to require a graded source of an inducing signal. Thus, the Drosophila CNS midline cells play a central inductive role in patterning the mesoderm as well as the underlying ectoderm.