bluuebunny/crossref_metadata_2025_split huggingface dataset:
The SH2-containing tyrosine phosphatase corkscrew is required during signaling by sevenless, Ras1 and Raf
Authors: Allard John D. , Chang Henry C. , Herbst Ronald , McNeill Helen , Simon Michael A. 
Published: April 2021

ABSTRACT
The sevenless gene encodes a receptor tyrosine kinase which is required for the development of the R7 photoreceptor cell in each ommatidium of the Drosophila eye. We have previously used a sensitized genetic screen to identify mutations, designated Enhancers of sevenless (E(sev)), which affect genes that encode components of the sevenless signaling pathway. Here, we report that one of these mutations, E(sev)1Ae0P is a dominantly inhibiting allele of corkscrew, which encodes an SH2 domain-containing protein tyrosine phosphatase (Perkins et al., 1992). We show that corkscrew function is essential for sevenless signaling and that expression of a membrane-targeted form of corkscrew can drive R7 photoreceptor development in the absence of sevenless function. Furthermore, we have used the dominantly inhibiting corkscrew allele to examine the role of corkscrew during signaling by activated forms of Ras1 and Raf. Our analysis indicates that corkscrew function is still required during signaling by activated Ras1 and Raf proteins. These results define a function for corkscrew that is either downstream of Ras1 activation or in a parallel pathway that acts with activated Ras1/Raf to specify R7 photoreceptor development.
The Drosophila morphogenetic protein Bicoid binds DNA cooperatively
Authors: Ma Xiuguang , Yuan Dong , Diepold Katharina , Scarborough Tom , Ma Jun 
Published: April 2021

ABSTRACT
The Drosophila morphogenetic protein Bicoid, encoded by the maternal gene bicoid, is required for the development of the anterior structures in the embryo. Bicoid, a transcriptional activator containing a homeodomain, is distributed in an anterior-to-posterior gradient in the embryo. In response to this gradient, the zygotic gene hunchback is expressed uniformly in the anterior half of the embryo in a nearly all- or-none manner. In this report we demonstrate that a recombinant Bicoid protein binds cooperatively to its sites within a hunchback enhancer element. A less than 4-fold increase in Bicoid concentration is sufficient to achieve an unbound/bound transition in DNA binding. Using various biochemical and genetic methods we further demonstrate that Bicoid molecules can interact with each other. Our results are consistent with previous studies performed in the embryo, and they suggest that one mechanism to achieve a sharp on/off switch of gene expression in response to a morphogenetic gradient is cooperative DNA binding facilitated by protein-protein interaction.
Conservation in hedgehog signaling: induction of a chicken patched homolog by Sonic hedgehog in the developing limb
Authors: Marigo Valeria , Scott Matthew P. , Johnson Ronald L. , Goodrich Lisa V. , Tabin Clifford J. 
Published: April 2021

ABSTRACT
Hedgehog genes have been implicated in inductive signaling during development in a variety of organisms. A key element of the hedgehog signaling system is encoded by the gene patched. In Drosophila hedgehog regulates gene expression by antagonizing the action of patched. In addition, patched is itself a transcriptional target of hedgehog signaling.
We have isolated a chicken patched homolog and find it to be strongly expressed adjacent to all tissues where members of the hedgehog family are expressed. As in Drosophila, ectopic expression of Sonic hedgehog leads to ectopic induction of chicken Patched. Based on this regulatory conservation, vertebrate Patched is likely to be directly downstream of Sonic hedgehog signaling.
An important role of Sonic hedgehog is the regulation of anterior/posterior pattern in the developing limb bud. Since Patched is directly downstream of the hedgehog signal, the extent of high level Patched expression provides a measure of the distance that Sonic hedgehog diffuses and directly acts. On this basis, we find that Sonic hedgehog directly acts as a signal over only the posterior third of the limb bud.
During limb patterning, secondary signals are secreted in both the mesoderm (e.g. Bone Morphogenetic Protein-2) and apical ectodermal ridge (e.g. Fibroblast Growth Factor-4) in response to Sonic hedgehog. Thus knowing which is the direct target tissue is essential for unraveling the molecular patterning of the limb. The expression of Patched provides a strong indication that the mesoderm and not the ectoderm is the direct target of Sonic hedgehog signaling in the limb bud.
Finally we demonstrate that induction of Patched requires Sonic hedgehog but, unlike Bone Morphogenetic Protein-2 and Hox genes, does not require Fibroblast Growth Factor as a co-inducer. It is therefore a more direct target of Sonic hedgehog than previously reported pat-terning genes.
Segregation of germ granules in living Caenorhabditis elegans embryos: cell-type-specific mechanisms for cytoplasmic localisation
Authors: Hird Steven N. , Paulsen Janet E. , Strome Susan 
Published: April 2021

ABSTRACT
Germ granules are ribonucleoprotein particles that are thought to function in germline specification in invertebrates and possibly in vertebrates. In Caenorhabditis elegans, these structures, termed P granules, are partitioned to the germline P cells during the early embryonic divisions. By injecting a fluorescently labelled anti-P-granule antibody into the C. elegans germline syncitium, we followed P-granule segregation in live embryos using laser-scanning confocal microscopy. We show that, in early P cells (P0 and P1), P-granule partitioning is achieved primarily by their migration through the cytoplasm towards the site of formation of the germline daughter cell. A different mechanism appears to operate in later P cells (P2 and P3): P granules associate with the nucleus and move with it toward the site of formation of the germline daughter cell, where they are then deposited. At each division, there is also disassembly or degradation of those P granules that remain in the cytoplasm destined for the somatic daughter cell. Microfilaments, microtubules and the product of the gene mes-1 are required for the normal pattern of P-granule segregation in P2.
Characterizing the zebrafish organizer: microsurgical analysis at the early-shield stage
Authors: Shih John , Fraser Scott E. 
Published: April 2021

ABSTRACT
The appearance of the embryonic shield, a slight thickening at the leading edge of the blastoderm during the formation of the germ ring, is one of the first signs of dorsoventral polarity in the zebrafish embryo. It has been proposed that the shield plays a role in fish embryo patterning similar to that attributed to the amphibian dorsal lip. In a recent study, we fate mapped many of the cells in the region of the forming embryonic shield, and found that neural and mesodermal progenitors are intermingled (Shih, J. and Fraser, S. E. (1995) Development 121, 2755-2765), in contrast to the coherent region of mesodermal progenitors found at the amphibian dorsal lip. Here, we examine the fate and the inductive potential of the embryonic shield to determine if the intermingling reflects a different mode of embryonic patterning than that found in amphibians. Using the microsurgical techniques commonly used in amphibian and avian experimental embryology, we either grafted or deleted the region of the embryonic shield. Homotopic grafting experiments confirmed the fates of cells within the embryonic shield region, showing descendants in the hatching gland, head mesoderm, notochord, somitic mesoderm, endoderm and ventral aspect of the neuraxis. Heterotopic grafting experiments demonstrated that the embryonic shield can organize a second embryonic axis; however, contrary to our expectations based on amphibian research, the graft contributes extensively to the ectopic neuraxis. Microsurgical deletion of the embryonic shield region at the onset of germ ring formation has little effect on neural development: embryos with a well-formed and well-patterned neuraxis develop in the complete absence of notochord cells. While these results show that the embryonic shield is sufficient for ectopic axis formation, they also raise questions concerning the necessity of the shield region for neural induction and embryonic patterning after the formation of the germ ring.
Two distinct endothelial lineages in ontogeny, one of them related to hemopoiesis
Authors: Pardanaud Luc , Luton Dominique , Prigent Magali , Bourcheix Laurent-Marie , Catala Martin , Dieterlen-Lièvre Françoise 
Published: April 2021

ABSTRACT
We have shown previously by means of quail/chick transplantations that external and visceral organs, i.e., somatopleural and splanchnopleural derivatives, acquire their endothelial network through different mechanisms, namely immigration (termed angiogenesis) versus in situ emergence of precursors (or vasculogenesis).
We have traced the distribution of QH1-positive cells in chick hosts after replacement of the last somites by quail somites (orthotopic grafts) or lateral plate mesoderm (heterotopic grafts). The results lead to the conclusion that the embryo becomes vascularized by endothelial precursors from two distinct regions, splanchnopleural mesoderm and paraxial mesoderm. The territories respectively vascularized are complementary, precursors from the paraxial mesoderm occupy the body wall and kidney, i.e., they settle along with the other paraxial mesoderm derivatives and colonize the somatopleure.
The precursors from the two origins have distinct recognition and potentialities properties: endothelial precursors of paraxial origin are barred from vascularizing visceral organs and from integrating into the floor of the aorta, and are never associated with hemopoiesis; splanchnopleural mesoderm grafted in the place of somites, gives off endothelial cells to body wall and kidney but also visceral organs. It gives rise to hemopoietic precursors in addition to endothelial cells.
The chinless mutation and neural crest cell interactions in zebrafish jaw development
Authors: Schilling Thomas F. , Walker Charline , Kimmel Charles B. 
Published: April 2021

ABSTRACT
During vertebrate development, neural crest cells are thought to pattern many aspects of head organization, including the segmented skeleton and musculature of the jaw and gills. Here we describe mutations at the gene chinless, chn, that disrupt the skeletal fates of neural crest cells in the head of the zebrafish and their interactions with muscle precursors. chn mutants lack neural-crest-derived cartilage and mesoderm-derived muscles in all seven pharyngeal arches. Fate mapping and gene expression studies demonstrate the presence of both undifferentiated cartilage and muscle precursors in mutants. However, chn blocks differentiation directly in neural crest, and not in mesoderm, as revealed by mosaic analyses. Neural crest cells taken from wild-type donor embryos can form cartilage when transplanted into chn mutant hosts and rescue some of the patterning defects of mutant pharyngeal arches. In these cases, cartilage only forms if neural crest is transplanted at least one hour before its migration, suggesting that interactions occur transiently in early jaw precursors. In contrast, transplanted cells in paraxial mesoderm behave according to the host genotype; mutant cells form jaw muscles in a wild-type environment. These results suggest that chn is required for the development of pharyngeal cartilages from cranial neural crest cells and subsequent crest signals that pattern mesodermally derived myocytes.
Effects of GGF/neuregulins on neuronal survival and neurite outgrowth correlate with erbB2/neu expression in developing rat retina
Authors: Bermingham-McDonogh Olivia , McCabe Kathryn L. , Reh Thomas A. 
Published: April 2021

ABSTRACT
We have examined the expression of neuregulin and its putative receptors, erbB2/neu, erbB3 and erbB4/tyro2 during retinal development, and tested several potential functions of this class of molecules in dissociated rat retinal cell cultures. At least one form of neuregulin is expressed in the retina, from the earliest stages of retinal development examined; in addition, all three of the known receptors are expressed by retinal neurons in a developmentally regulated manner. When added to cultures of embryonic or neonatal rat retinal cells, neuregulin (rhGGF2) promotes survival and neurite extension from retinal neurons in a dose-dependent manner. These results indicate that in addition to their well described effects on glia, the neuregulins also have direct effects on central nervous system neurons.
Notochord signals control the transcriptional cascade of myogenic bHLH genes in somites of quail embryos
Authors: Pownall Mary Elizabeth , Strunk Karen E. , Emerson Charles P. 
Published: April 2021

ABSTRACT
Microsurgical, tissue grafting and in situ hybridization techniques have been used to investigate the role of the neural tube and notochord in the control of the myogenic bHLH genes, QmyoD, Qmyf5, Qmyogenin and the cardiac α-actin gene, during somite formation in stage 12 quail embryos. Our results reveal that signals from the axial neural tube/notochord complex control both the activation and the maintenance of expression of QmyoD and Qmyf5 in myotomal progenitor cells during the period immediately following somite formation and prior to myotome differentiation. QmyoD and Qmyf5 expression becomes independent of axial signals during myotome differentiation when somites activate expression of Qmyogenin and α-actin. Ablation studies reveal that the notochord controls QmyoD activation and the initiation of the transcriptional cascade of myogenic bHLH genes as epithelial somites condense from segmental plate mesoderm. The dorsal medial neural tube then contributes to the maintenance of myogenic bHLH gene expression in newly formed somites. Notochord grafts can activate ectopic QmyoD expression during somite formation, establishing that the notochord is a necessary and sufficient source of diffusible signals to initiate QmyoD expression. Myogenic bHLH gene expression is localized to dorsal medial cells of the somite by inhibitory signals produced by the lateral plate and ventral neural tube. Signaling models for the activation and maintenance of myogenic gene expression and the determination of myotomal muscle in somites are discussed.
Altering cell fates in sea urchin embryos by overexpressing SpOtx, an orthodenticle-related protein
Authors: Mao Chai-An , Wikramanayake Athula H. , Gan Lin , Chuang Chin-Kai , Summers Robert G. , Klein William H. 
Published: April 2021

ABSTRACT
While many general features of cell fate specification in the sea urchin embryo are understood, specific factors associated with these events remain unidentified. SpOtx, an orth-odenticle-related protein, has been implicated as a transcriptional activator of the aboral ectoderm-specific Spec2a gene. Here, we present evidence that SpOtx has the potential to alter cell fates. SpOtx was found in the cytoplasm of early cleavage stage embryos and was translocated into nuclei between the 60- and 120-cell stage, coincident with Spec gene activation. Eggs injected with SpOtx mRNA developed into epithelial balls of aboral ectoderm suggesting that SpOtx redirected nonaboral ectoderm cells to an aboral ectoderm fate. At least three distinct domains on SpOtx, the homeobox and regions in the N-terminal and C-terminal halves of the protein, were required for the morphological alterations. These same N-terminal and C-terminal regions were shown to be transactivation domains in a yeast transactivation assay, indicating that the biological effects of overexpressing SpOtx were due to its action as a transcription factor. Our results suggest that SpOtx is involved in aboral ectoderm differentiation by activating aboral ectoderm-specific genes and that modulating its expression can lead to changes in cell fate.
The TGF-β signaling pathway is essential for Drosophila oogenesis
Authors: Twombly Vern , Blackman Ronald K. , Jin Hui , Graff Jonathan M. , Padgett Richard W. , Gelbart William. M. 
Published: April 2021

ABSTRACT
We examine roles of signaling by secreted ligands of the TGF-β family during Drosophila oogenesis. One family member, the DPP ligand encoded by the decapentaplegic (dpp) gene, is required for patterning of anterior eggshell structures. This requirement presumably reflects the expression pattern of dpp in an anterior subset of somatic follicle cells: the centripetally migrating and the nurse cell-associated follicle cells. Similar requirements are also revealed by mutations in the saxophone (sax)-encoded receptor, consistent with the idea that DPP signaling is, at least in part, mediated by the SAX receptor. A loss of germline sax function results in a block in oogenesis associated with egg chamber degeneration and a failure of the transfer of nurse cell contents to the oocyte, indicating that TGF-β signaling is required for these events. Some phenotypes of sax mutations during oogenesis suggest that SAX responds to at least one other TGF-β ligand as well in the posterior follicle cells.
Two independent and polarized processes of cell elongation regulate leaf blade expansion in Arabidopsis thaliana (L.) Heynh.
Authors: Tsuge Tomohiko , Tsukaya Hirokazu , Uchimiya Hirofumi 
Published: April 2021

ABSTRACT
For genetic analysis of mechanisms of leaf morphogenesis, we chose Arabidopsis thaliana (L.) Heynh. as a model for leaf development in dicotyledonous plants. Leaves of the angustifolia mutant were the same length as but narrower and thicker than wild-type leaves. The total number of cells in leaf blades of angustifolia plants was the same as in the wild type. At the cellular level in the angustifolia mutant it was found that the cells were smaller in the leaf-width direction and larger in the leaf-thickness direction than in wild type, revealing the function of the ANGUSTIFOLIA gene, which is to control leaf morphology by regulating polarity-specific cell elongation. The existence of similar genes that regulate leaf development in the length direction was, therefore, predicted. Three loci and several alleles associated with short-leaved mutants were newly isolated as rotundifolia mutants. The rotundifolia3 mutant had the same number of cells as the wild type, with reduced cell elongation in the leaf-length direction. The features of the angustifolia rotundifolia3 double mutant indicated that ANGUSTIFOLIA and ROTUNDIFOLIA3 genes act independently. We propose that leaf expansion in Arabidopsis involves at least two independent developmental processes: width development and length development, with the ANGUSTIFOLIA and ROTUNDIFOLIA3 genes playing different polarity-specific roles in cell elongation.
The maize mutant narrow sheath fails to establish leaf margin identity in a meristematic domain
Authors: Scanlon Michael J. , Schneeberger Richard G. , Freeling Michael 
Published: April 2021

ABSTRACT
The maize mutant narrow sheath (ns) displays a leaf shape and plant stature phenotype that suggests the preprimordial deletion of a leaf domain. The ns mutant phenotype is inherited as a recessive, duplicate-factor trait, conditioned upon homozygosity for each of the two unlinked mutations narrow sheath-1 (ns1) and narrow sheath-2 (ns2). Mutant leaves are missing a large domain including the leaf margin, and mutant internodes are shortened on the marginal side of the stem. This domain deletion extends from the internode to beyond the longitudinal mid-length of the blade, and corresponds to an alteration in the organization of a specific region of the shoot apical meristem. The premargin region of mutant founder cells fail to down-regulate expression of Knox genes, markers of nonleaf meristematic identity. Our results indicate that leaf domains may acquire identity in the meristem itself, and that the subdivision of preprimordial developmental fields into differential domains is a common feature of both plant and animal organogenesis.
Complex expression of the zp-50 pou gene in the embryonic zebrafish brain is altered by overexpression of sonic hedgehog
Authors: Hauptmann Giselbert , Gerster Thomas 
Published: April 2021

ABSTRACT
We report the characterization of the zebrafish zp-50 class III POU domain gene. This gene is first activated in the prospective diencephalon after the end of the gastrula period. During somitogenesis, zp-50 is expressed in a very dynamic and complex fashion in all major subdivisions of the central nervous system. After one day of development, zp-50 transcripts are present in the fore- and midbrain in several distinct cell clusters. In the hindbrain, zp-50 expression is found in two types of domains. Correct zp-50 expression in the ventral fore- and midbrain requires genes known to be involved in dorsoventral patterning of the zebrafish CNS. Transcripts of the sonic hedgehog (shh) gene encoding an intercellular signaling molecule are detected in the forming diencephalon shortly prior to the appearance of zp-50 mRNA. Correct expression in this region of both shh, and zp-50, requires a functional cyclops (cyc) locus: shh and zp-50 transcripts are likewise absent from the ventral rostral brain of mutant cyc−/− embryos. Injection of synthetic shh mRNA into fertilized eggs causes ectopic zp-50 expression at more dorsal positions of the embryonic brain. The close spatial and temporal coincidence of expression in the rostral brain, the similar response to the cyc− mutation, and the ectopic zp-50 expression in the injection experiments all suggest that zp-50 may directly respond to the reception of the Shh signal.
Cell fate determination in an annelid equivalence group
Authors: Huang Françoise Z. , Weisblat David A. 
Published: April 2021

ABSTRACT
In embryos of glossiphoniid leeches such as Helobdella triserialis and H. robusta, pairs of adjacent ‘o/p’ ectodermal blast cells are known to be developmentally equipotent and yet eventually contribute distinct sets of ‘O’ and ‘P’ progeny to the nervous system and epidermis of the mature leech. It has been thought that the fate-determining interactions in this ‘O-P equivalence group’ take place between the equipotent cells themselves. We show here that such intra-group interactions are neither necessary nor sufficient. Instead, transient contact with cells in another ectodermal lineage is necessary and sufficient to induce o/p blast cells to assume the P fate. In the absence of this contact they assume the O fate.