bluuebunny/crossref_metadata_2025_split huggingface dataset:
A processed form of the Spätzle protein defines dorsal-ventral polarity in the Drosophila embryo
Authors: Schneider David S. , Jin Yishi , Morisato Donald , Anderson Kathryn V. 
Published: April 2021

ABSTRACT
Stein et al. (1991) identified a soluble, extracellular factor that induces ventral structures at the site where it is injected in the extracellular space of the early Drosophila embryo. This factor, called polarizing activity, has the properties predicted for a ligand for the transmembrane receptor encoded by the Toll gene. Using a bioassay to follow activity, we purified a 24×103Mr protein that has polarizing activity. The purified protein is recognized by antibodies to the C-terminal half of the Spätzle protein, indicating that this polarizing activity is a product of the spätzle gene. The purified protein is smaller than the primary translation product of spätzle, suggesting that proteolytic processing of Spätzle on the ventral side of the embryo is required to generate the localized, active form of the protein.
A POU gene required for early cleavage and protein accumulation in the sea urchin embryo
Authors: Char Bharat R. , Tan Hongying , Maxson Rob 
Published: April 2021

ABSTRACT
SpOct is a POU gene expressed during oogenesis and early embryogenesis of the sea urchin, Strongylocentrotus purpu -ratus. In the first use of antisense technology in the sea urchin embryo, we report that disruption of SpOct gene function in 1-cell zygotes by the injection of antisense oligodeoxynucleotides arrests development prior to the first cell division. We show that single-stranded antisense oligodeoxynucleotides specifically block cleavage, and that injection of SpOct mRNA overcomes this block. The accumulation of [35S]methionine into zygotically synthesized protein is significantly reduced in antisense-injected embryos. DNA synthesis is also reduced by the antisense regimen as expected from the antisense inhibition of protein accumulation. That protein accumulation prior to the first cleavage is retarded by antisense targeting of a transcription factor is very surprising in light of classical work showing that the activation of protein synthesis does not require zygotic transcription. We conclude that either some new transcription is obligate for the accumulation of new protein, or that the SpOct gene plays a novel, non-transcriptional role in this process.
Confrontation of scabrous expressing and non-expressing cells is essential for normal ommatidial spacing in the Drosophila eye
Authors: Ellis Michael C. , Weber Ursula , Wiersdorff Volker , Mlodzik Marek 
Published: April 2021

ABSTRACT
The establishment of neural precursor cells in Drosophila depends on cell-cell interactions and lateral inhibition. Scabrous (sca) is involved in this process by preventing an excess of cells from adopting a neural precursor fate. Specifically in eye development, Sca protein function has been implicated in the spacing pattern that is essential for the ordered appearance of the ommatidial array. During this process sca expression is restricted to neurogenic groups of cells and later to the neural precursors. We report that ectopic sca expression in the morphogenetic furrow results in a rough eye phenotype with oversized and fused ommatidia. These defects in adult eyes are due to the generation of too many ommatidial preclusters in the morphogenetic furrow. Strikingly, sca loss-of-function mutants have an almost identical phenotype. Our results suggest that Sca plays a positive role in establishing the spacing pattern within the furrow and that the quantitative difference in sca expression between neighboring groups of cells is a determining factor in this process. Ectopic expression of Sca also represses endogenous sca expression in the furrow, suggesting that Sca is involved in a feedback loop affecting its own transcription. Interestingly, sca shares homology to a group of extracellular matrix proteins that have been implicated in neuronal differentiation. We present a model for sca function based on its phenotypic and molecular features.
Dissecting the temporal requirements for homeotic gene function
Authors: Castelli-Gair James , Greig Stephen , Micklem Gos , Akam Michael 
Published: April 2021

ABSTRACT
Homeotic genes confer identity to the different segments of Drosophila. These genes are expressed in many cell types over long periods of time. To determine when the homeotic genes are required for specific developmental events we have expressed the Ultrabithorax, abdominal-A and Abdominal-Bm proteins at different times during development using the GAL4 targeting technique. We find that early transient homeotic gene expression has no lasting effects on the differentiation of the larval epidermis, but it switches the fate of other cell types irreversibly (e.g. the spiracle primordia). We describe one cell type in the peripheral nervous system that makes sequential, independent responses to homeotic gene expression. We also provide evidence that supports the hypothesis of in vivo competition between the bithorax complex proteins for the regulation of their down-stream targets.
Morphogenesis of Drosophila ovarian ring canals
Authors: Robinson Douglas N. , Cant Kelly , Cooley Lynn 
Published: April 2021

ABSTRACT
We analyzed the structure of cytoplasmic bridges called ring canals in Drosophila egg chambers. Two mutations, hu-li tai shao (hts) and kelch, disrupt normal ring canal development. We raised antibodies against the carboxyterminal tail of hts and found that they recognize a protein that localizes specifically to ring canals very early in ring canal assembly. Accumulation of filamentous actin on ring canals coincides with the appearance of the hts protein. kelch, which is localized to the ring canals hours after hts and actin, is necessary for maintaining a highly ordered ring canal rim since kelch mutant egg chambers have ring canals that are obstructed by disordered actin and hts. Anti-phosphotyrosine antibodies immunostain ring canals beginning early in the germarium before hts and actin and throughout egg chamber development. The use of antibody reagents to analyze the structure of wild-type and mutant ring canals has shown that ring canal development is a dynamic process of cytoskeletal protein assembly, possibly regulated by tyrosine phosphorylation of some ring canal components.
Drosophila virilis oskar transgenes direct body patterning but not pole cell formation or maintenance of mRNA localization in D. melanogaster
Authors: Webster Philippa J. , Suen Jeffrey , Macdonald Paul M. 
Published: April 2021

ABSTRACT
The Drosophila melanogaster gene oskar is required for both posterior body patterning and germline formation in the early embryo; precisely how oskar functions is unknown. The oskar transcript is localized to the posterior pole of the developing oocyte, and oskar mRNA and protein are maintained at the pole through early embryogenesis. The posterior maintenance of oskar mRNA is dependent upon the presence of oskar protein. We have cloned and characterized the Drosophila virilis oskar homologue, virosk, and examined its activity as a transgene in Drosophila melanogaster flies. We find that the cis-acting mRNA localization signals are conserved, although the virosk transcript also transiently accumulates at novel intermediate sites. The virosk protein, however, shows substantial differences from oskar: while virosk is able to rescue body patterning in a D. melanogaster oskar− background, it is impaired in both mRNA maintenance and pole cell formation. Furthermore, virosk induces a dominant maternal-effect lethality when introduced into a wild-type background, and interferes with the posterior maintenance of the endogenous oskar transcript in early embryogenesis. Our data suggest that virosk protein is unable to anchor at the posterior pole of the early embryo; this defect could account for all of the characteristics of virosk mentioned above. Our observations support a model in which oskar protein functions both by nucleating the factors necessary for the activation of the posterior body patterning determinant and the germ cell determinant, and by anchoring these factors to the posterior pole of the embryo. While the posterior body patterning determinant need not be correctly localized to provide body patterning activity, the germ cell determinant may need to be highly concentrated adjacent to the cortex in order to direct pole cell formation.
glp-1 and inductions establishing embryonic axes in C. elegans
Authors: Hutter Harald , Schnabel Ralf 
Published: April 2021

ABSTRACT
Two successive inductions specify blastomere identities, that is complex cell lineages and not specific tissues, in a major part of the early C. elegans embryo. The first induction acts along the anterior-posterior axis of the embryo and the second along the left-right axis. During the first induction a specific lineage program is induced in the posterior of the two AB blastomeres present in the four cell embryo. During the second induction, almost all of the left-right differences of the embryo are specified by interactions between a single signalling blastomere, MS, and the AB blastomeres that surround it. In both cases the inductions break the equivalence of pairs of blastomeres. The inductions correlate with the cell-cell contacts to the inducing blastomeres. The stereotype cleavage pattern of the early embryo results in invariant cell-cell contacts that guarantee the specificity of the inductions. Both inductions are affected in embryos mutant for glp-1 suggesting that in both cases glp-1 is involved in the reception of the signal.
Specific roles of the αVβ1, αVβ3 and αVβ5 integrins in avian neural crest cell adhesion and migration on vitronectin
Authors: Delannet Muriel , Martin Fabrice , Bossy Blaise , Cheresh David A. , Reichardt Louis F. , Duband Jean-Loup 
Published: April 2021

ABSTRACT
To identify potentially important extracellular matrix adhesive molecules in neural crest cell migration, the possible role of vitronectin and its corresponding integrin receptors was examined in the adhesion and migration of avian neural crest cells in vitro. Adhesion and migration on vitronectin were comparable to those found on fibronectin and could be almost entirely abolished by antibodies against vitronectin and by RGD peptides. Immunoprecipitation and immunocytochemistry analyses revealed that neural crest cells expressed primarily the αVβ1, αVβ3 and αVβ5 integrins as possible vitronectin receptors. Inhibition assays of cellular adhesion and migration with functionperturbing antibodies demonstrated that adhesion of neural crest cells to vitronectin was mediated essentially by one or more of the different αV integrins, with a possible preeminence of αVβ1, whereas cell migration involved mostly the αVβ3 and αVβ5 integrins. Immunofluorescence labeling of cultured motile neural crest cells revealed that the αV integrins are differentially distributed on the cell surface. The β1 and αV subunits were both diffuse on the surface of cells and in focal adhesion sites in association with vinculin, talin and α-actinin, whereas the αVβ3 and αVβ5 integrins were essentially diffuse on the cell surface. Finally, vitronectin could be detected by immunoblotting and immunohistochemistry in the early embryo during the ontogeny of the neural crest. It was in particular closely associated with the surface of migrating neural crest cells. In conclusion, our study indicates that neural crest cells can adhere to and migrate on vitronectin in vitro by an RGD-dependent mechanism involving at least the αVβ1, αVβ3 and αVβ5 integrins and that these integrins may have specific roles in the control of cell adhesion and migration.
Heparan sulfate proteoglycans are required for mesoderm formation in Xenopus embryos
Authors: Itoh Keiji , Sokol Sergei Y. 
Published: April 2021

ABSTRACT
Mesoderm forms in the vertebrate embryo as a result of inductive interactions involving secreted growth factors and cell surface molecules. Proteoglycans have recently been implicated in the control of cell adhesion, migration and growth factor responsiveness. We have found that removal of glycosaminoglycan chains of proteoglycans from Xenopus ectodermal explants by heparinase, but not by chondroitinase, results in inhibition of elongation and mesodermal differentiation in response to signaling factors: activin, FGF and Wnt. Heparinase treatment differentially affected expression of early general and regionspecific mesodermal markers, suggesting that mesodermal cell fates become specified in the early embryo via at least two signaling pathways which differ in their requirements for heparan sulfate proteoglycans. Addition of soluble heparan sulfate restored activin-mediated induction of muscle-specific actin gene in heparinase-treated explants. Finally, heparinase inhibited autonomous morphogenetic movements and mesodermal, but not neural, differentiation in dorsal marginal zone explants, which normally give rise to mesoderm in the embryo. These results directly demonstrate that heparan sulfate proteoglycans participate in gastrulation and mesoderm formation in the early embryo.
Expression of a dominant negative inhibitor of intercellular communication in the early Xenopus embryo causes delamination and extrusion of cells
Authors: Paul D. L. , Yu K. , Bruzzone R. , Gimlich R. L. , Goodenough D. A. 
Published: April 2021

ABSTRACT
A chimeric construct, termed 3243H7, composed of fused portions of the rat gap junction proteins connexin32 (Cx32) and connexin43 (Cx43) has been shown to have selective dominant inhibitory activity when tested in the Xenopus oocyte pair system. Co-injection of mRNA coding for 3243H7 together with mRNAs coding for Cx32 or Cx43 completely blocked the development of channel conductances, while the construct was ineffective at blocking intercellular channel assembly when coinjected with rat connexin37 (Cx37). Injection of 3243H7 into the right anterodorsal blastomere of 8-cell-stage Xenopus embryos resulted in disadhesion and delamination of the resultant clone of cells evident by embryonic stage 8; a substantial number, although not all, of the progeny of the injected cell were eliminated from the embryo by stage 12. A second construct, 3243H8, differing from 3243H7 in the relative position of the middle splice, had no dominant negative activity in the oocyte pair assay, nor any detectable effects on Xenopus development, even when injected at four-fold higher concentrations. The 3243H7-induced embryonic defects could be rescued by coinjection of Cx37 with 3243H7. A blastomere reaggregation assay was used to demonstrate that a depression of dye-transfer could be detected in 3243H7-injected cells as early as stage 7; Lucifer yellow injections into single cells also demonstrated that injection of 3243H7 resulted in a block of intercellular communication. These experiments indicate that maintenance of embryonic cell adhesion with concomitant positional information requires gap junction-mediated intercellular communication.
The identification of genes with unique and essential functions in the development of the zebrafish, Danio rerio
Authors: Haffter Pascal , Granato Michael , Brand Michael , Mullins Mary C. , Hammerschmidt Matthias , Kane Donald A. , Odenthal Jörg , J. M. van Eeden Fredericus , Jiang Yun-Jin , Heisenberg Carl-Philipp , Kelsh Robert N. , Furutani-Seiki Makoto , Vogelsang Elisabeth , Beuchle Dirk , Schach Ursula , Fabian Cosima , Nüsslein-Volhard Christiane 
Published: April 2021

ABSTRACT
In a large-scale screen, we isolated mutants displaying a specific visible phenotype in embryos or early larvae of the zebrafish, Danio rerio. Males were mutagenized with ethylnitrosourea (ENU) and F2 families of single pair matings between sibling F1 fish, heterozygous for a mutagenized genome, were raised. Egg lays were obtained from several crosses between F2 siblings, resulting in scoring of 3857 mutagenized genomes. F3 progeny were scored at the second, third and sixth day of development, using a stereo-microscope. In a subsequent screen, fixed embryos were analyzed for correct retinotectal projection. A total of 4264 mutants were identified. Two thirds of the mutants displaying rather general abnormalities were eventually discarded. We kept and characterized 1163 mutants. In complementation crosses performed between mutants with similar phenotypes, 894 mutants have been assigned to 372 genes. The average allele frequency is 2.4. We identified genes involved in early development, notochord, brain, spinal cord, somites, muscles, heart, circulation, blood, skin, fin, eye, otic vesicle, jaw and branchial arches, pigment pattern, pigment formation, gut, liver, motility and touch response. Our collection contains alleles of almost all previously described zebrafish mutants. From the allele frequencies and other considerations we estimate that the 372 genes defined by the mutants probably represent more than half of all genes that could have been discovered using the criteria of our screen. Here we give an overview of the spectrum of mutant phenotypes obtained, and discuss the limits and the potentials of a genetic saturation screen in the zebrafish.
Mutations affecting development of the notochord in zebrafish
Authors: Stemple Derek L. , Solnica-Krezel Lilianna , Zwartkruis Fried , Neuhauss Stephan C. F. , Schier Alexander F. , Malicki Jarema , Stainier Didier Y. R. , Abdelilah Salim , Rangini Zehava , Mountcastle-Shah Elizabeth , Driever Wolfgang 
Published: April 2021

ABSTRACT
The notochord is critical for the normal development of vertebrate embryos. It serves both as the major skeletal element of the embryo and as a signaling source for the establishment of pattern within the neurectoderm, the paraxial mesoderm and other tissues. In a large-scale systematic screen of mutations affecting embryogenesis in zebrafish we identified 65 mutations that fall into 29 complementation groups, each leading to a defect in the formation and/or maintenance of the notochord. These mutations produce phenotypic abnormalities at numerous stages of notochord development, thereby establishing a phenotypic pathway, which in turn suggests a genetic pathway for the development of the notochord. Perturbations within adjacent tissues in mutant embryos further indicate the importance of notochord-derived signals for patterning within the embryo and suggest that these mutations will yield additional insight into the cues that regulate these patterning processes.
Mutations affecting development of the midline and general body shape during zebrafish embryogenesis
Authors: Brand Michael , Heisenberg Carl-Philipp , Warga Rachel M. , Pelegri Francisco , Karlstrom Rolf O. , Beuchle Dirk , Picker Alexander , Jiang Yun-Jin , Furutani-Seiki Makoto , Eeden Fredericus J. M. van , Granato Michael , Haffter Pascal , Hammerschmidt Matthias , Kane Donald A. , Kelsh Robert N. , Mullins Mary C. , Odenthal Jörg , Nüsslein-Volhard Christiane 
Published: April 2021

ABSTRACT
Tissues of the dorsal midline of vertebrate embryos, such as notochord and floor plate, have been implicated in inductive interactions that pattern the neural tube and somites. In our screen for embryonic visible mutations in the zebrafish we found 113 mutations in more than 27 genes with altered body shape, often with additional defects in CNS development. We concentrated on a subgroup of mutations in ten genes (the midline-group) that cause defective development of the floor plate. By using floor plate markers, such as the signaling molecule sonic hedgehog, we show that the schmalspur (sur) gene is needed for early floor plate development, similar to one-eyed-pinhead (oep) and the previously described cyclops (cyc) gene. In contrast to oep and cyc, sur embryos show deletions of ventral CNS tissue restricted to the mid- and hindbrain, whereas the forebrain appears largely unaffected. In the underlying mesendodermal tissue of the head, sur is needed only for development of the posterior pre-chordal plate, whereas oep and cyc are required for both anterior and posterior prechordal plate development. Our analysis of sur mutants suggests that defects within the posterior prechordal plate may cause aberrant development of ventral CNS structures in the mid- and hindbrain. Later development of the floor plate is affected in mutant chameleon, you-too, sonic-you, iguana, detour, schmalhans and monorail embryos; these mutants often show additional defects in tissues that are known to depend on signals from notochord and floor plate. For example, sur, con and yot mutants show reduction of motor neurons; median deletions of brain tissue are seen in sur, con and yot embryos; and cyc, con, yot, igu and dtr mutants often show no or abnormal formation of the optic chiasm. We also find fusions of the ventral neurocranium for all midline mutants tested, which may reveal a hitherto unrecognized function of the midline in influencing differentiation of neural crest cells at their destination. As a working hypothesis, we propose that midline-group genes may act to maintain proper structure and inductive function of zebrafish midline tissues.
Mutations affecting neural survival in the zebrafish Danio rerio
Authors: Abdelilah Salim , Mountcastle-Shah Eliza , Harvey Michele , Solnica-Krezel Lilianna , Schier Alexander F. , Stemple Derek L. , Malicki Jarema , Neuhauss Stephan C. F. , Zwartkruis Fried , Stainier Didier Y. R. , Rangini Zehava , Driever Wolfgang 
Published: April 2021

ABSTRACT
Programmed cell death is a prominent feature of normal animal development. During neurogenesis, naturally occurring cell death is a mechanism to eliminate neurons that fail to make appropriate connections. To prevent accidental cell death, mechanisms that trigger programmed cell death, as well as the genetic components of the cell death program, are tightly controlled.
In a large-scale mutagenesis screen for embryonic lethal mutations in zebrafish Danio rerio we have found 481 mutations with a neural degeneration phenotype. Here, we present 50 mutations that fall into two classes (termed spacehead and fala-like) that are characterized by two main features: first, they appear to affect cell survival primarily within the neuroectodermal lineages during somitogenesis, and second, they show an altered brain morphology at or before 28 hours of development. Evidence for the specificity of cell death within the central nervous system comes from visual inspection of dying cells and analysis of DNA fragmentation, a process associated with apoptotic cell death. In mutants, the level of dying cells is significantly increased in brain and spinal cord. Furthermore, at the end of somitogenesis, the cell count of radial glia and trigeminal neurons is reduced in some mutants of the spacehead class.
A variety of neurodegenerative disorders in mouse and humans have been associated with abnormal levels of programmed cell death within the central nervous system. The mutations presented here might provide a genetic framework to aid in the understanding of the etiology of degenerative and physiological disorders within the CNS and the activation of inappropriate programmed cell death.