bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Drosophila toucan (toc) gene is required in germline cells for the somatic cell patterning during oogenesis
Authors: Grammont, Muriel , Dastugue Bernard , Couderc Jean-Louis 
Published: April 2021

ABSTRACT
We have characterized a new gene, called toucan, that is expressed and required in germline cells to promote proper differentiation of the somatic follicle cells. toucan mutant ovaries are defective in (i) the enclosure of newly formed germline cysts by the follicle cells, (ii) the formation of interfollicular stalks, (iii) the migration of the follicle cells over the oocyte and (iv) the formation of the eggshell. Overexpression of a toucan cDNA in the germline leads to the production of longer interfollicular stalks than wild-type ovaries, a phenotype that is the exact opposite of the toucan mutant phenotype. This observation shows that the formation of the interfollicular stalks depends not only on interactions among the somatic cells but also requires a germline signal. Moreover, dominant interactions have been observed between toucan and certain alleles of the daughterless, Notch and Delta genes, each of which is required in the somatic cells for the formation of egg chambers. toucan encodes for a large protein with a coiled-coil domain but has no other homology with known proteins. We propose that toucan participates in the production or localization of a germline-specific signal(s) that is required for the patterning of the follicular epithelium.
Regulation of the Twist target gene tinman by modular cis-regulatory elements during early mesoderm development
Authors: Yin Zhizhang , Xu Xiao-Lei , Frasch Manfred 
Published: April 2021

ABSTRACT
The Drosophila tinman homeobox gene has a major role in early mesoderm patterning and determines the formation of visceral mesoderm, heart progenitors, specific somatic muscle precursors and glia-like mesodermal cells. These functions of tinman are reflected in its dynamic pattern of expression, which is characterized by initial widespread expression in the trunk mesoderm, then refinement to a broad dorsal mesodermal domain, and finally restricted expression in heart progenitors. Here we show that each of these phases of expression is driven by a discrete enhancer element, the first being active in the early mesoderm, the second in the dorsal mesoderm and the third in cardioblasts. We provide evidence that the early-active enhancer element is a direct target of twist, a gene encoding a basic helix-loop-helix (bHLH) protein, which is necessary for tinman activation. This 180 bp enhancer includes three E-box sequences which bind Twist protein in vitro and are essential for enhancer activity in vivo. Ectodermal misexpression of twist causes ectopic activation of this enhancer in ectodermal cells, indicating that twist is the only mesoderm-specific activator of early tinman expression. We further show that the 180 bp enhancer also includes negatively acting sequences. Binding of Evenskipped to these sequences appears to reduce twistdependent activation in a periodic fashion, thus producing a striped tinman pattern in the early mesoderm. In addition, these sequences prevent activation of tinman by twist in a defined portion of the head mesoderm that gives rise to hemocytes. We find that this repression requires the function of buttonhead, a head-patterning gene, and that buttonhead is necessary for normal activation of the hematopoietic differentiation gene serpent in the same area. Together, our results show that tinman is controlled by an array of discrete enhancer elements that are activated successively by differential genetic inputs, as well as by closely linked activator and repressor binding sites within an early-acting enhancer, which restrict twist activity to specific areas within the twist expression domain.
Emergence of determined myotome precursor cells in the somite
Authors: Williams Brian A. , Ordahl Charles P. 
Published: April 2021

ABSTRACT
Myotome and sclerotome precursor cells are derived, respectively, from cells in the dorsomedial and ventromedial regions of the somite. To assay changes in the specification of myotomal precursor cells during somite maturation, we implanted dorsomedial quadrant fragments, from staged quail somites, next to the notochords of host chick embryos, and superimposed two additional notochords on these implants. In this notochord signalling environment, dorsomedial quadrant cells that are developmentally plastic are expected to differentiate as cartilage, while cells determined to a myogenic fate are expected to differentiate as skeletal muscle. Large numbers of differentiated chondrocytes developed from dorsomedial quadrant grafts of all stages of paraxial mesoderm development tested, indicating that persistent chondrogenic potential in cells fated to form muscle and dermis can be elicited by notochord signals. Differentiated myocytes, however, appeared in two somite-stage-dependent phases. In the first phase, dorsomedial quadrants from segmental plate and early stage somites (II and IV) form small, disorganized clusters of individual myocytes. The frequency of first-phase myocluster formation increases as myogenic factor expression begins in the dorsomedial quadrant, indicating that myogenic determination assayed by this method is closely linked to the expression of myogenic factors in the dorsomedial quadrant. In the second phase, dorsomedial quadrants from somite stages XI-XIII consistently form morphologically organized muscle tissue containing large numbers of parallel-oriented, multinucleated myotubes. Mitotic labelling demonstrated that muscle precursors were determined to the muscle phenotype prior to withdrawal from the cell cycle. Thus, myogenic determination in cells of the dorsomedial quadrant is acquired at earlier stages of somite maturation than the ability to proliferate and form muscle tissue. These results are consistent with the hypothesis that successive lineages of myotome precursor cells with different mitotic and morphogenetic properties arise in the dorsomedial quadrant during somite maturation.
Structure, function, and expression of SEL-1, a negative regulator of LIN-12 and GLP-1 in C. elegans
Authors: Grant Barth , Greenwald Iva 
Published: April 2021

ABSTRACT
Previous work indicated that sel-1 functions as a negative regulator of lin-12 activity, and predicted that SEL-1 is a secreted or membrane associated protein. In this study, we describe cell ablation experiments that suggest sel-1 mutations elevate lin-12 activity cell autonomously. We also use transgenic approaches to demonstrate that the predicted signal sequence of SEL-1 can direct secretion and is important for function, while a C-terminal hydrophobic region is not required for SEL-1 function. In addition, by analyzing SEL-1 localization using specific antisera we find that SEL-1 is localized intracellularly, with a punctate staining pattern suggestive of membrane bound vesicles. We incorporate these observations, and new information about a related yeast gene, into a proposal for a possible mechanism for SEL-1 function in LIN-12 turnover.
Two Eph receptor tyrosine kinase ligands control axon growth and may be involved in the creation of the retinotectal map in the zebrafish
Authors: Brennan Caroline , Monschau Bruno , Lindberg Rick , Guthrie Brenda , Drescher Uwe , Bonhoeffer Friedrich , Holder Nigel 
Published: April 2021

ABSTRACT
The isolation and characterisation of two zebrafish Eph receptor ligand cDNAs which we have called zfEphL3 and zfEphL4 is described. These genes are expressed in the presumptive midbrain of developing embryos from 6 somites. By 24 hours L3 is expressed throughout the midbrain including the region of the presumptive tectum whereas L4 is strongly expressed in the midbrain caudal to the presumptive tectum. At later stages of development L3 is expressed in a graded fashion throughout the tectum and L4 is maintained at its posterior margin. Growth cone collapse and pathway selection assays demonstrate that both these proteins have a collapse activity for retinal ganglion cells. When faced with a choice of substrate on which to grow, temporal axons from chick retinal ganglion cells selectively avoided membranes from Cos cells transfected with L3, whereas nasal axons did not. Both temporal and nasal axons avoided membranes from Cos cells transfected with L4. The expression patterns together with the functional data suggest that although both ligands may be able to guide retinal ganglion cells axons in vitro, they have different roles in the guidance of retinotectal projections in vivo. The expression of L3 is consistent with a role in the guidance of retinal ganglion cells to their targets on the tectum whereas that of L4 suggests a role in delineating the posterior boundary of the optic tectum.
TSO1 functions in cell division during Arabidopsis flower development
Authors: Liu Zhongchi , Running Mark P. , Meyerowitz Elliot M. 
Published: April 2021

ABSTRACT
We describe an Arabidopsis mutant, tso1, which develops callus-like tissues in place of floral organs. The tso1 floral meristem lacks properly organized three cell layers, and the nuclei of these cells are irregular in size and shape. Further analyses reveal partially formed cell walls and increased DNA ploidy in tso1 floral meristem cells, indicating defects in mitosis and cytokinesis. Our finding that TSO1 is required for organ formation in floral tissues but not in other tissues indicates that TSO1 may encode a floral-specific cell division component, or that TSO1 function is redundant in nonfloral tissues.
Importance of nidogen binding to laminin γ1 for branching epithelial morphogenesis of the submandibular gland
Authors: Kadoya Yuichi , Salmivirta Katriina , Talts Jan Fredrik , Kadoya Kuniko , Mayer Ulrike , Timpl Rupert , Ekblom Peter 
Published: April 2021

ABSTRACT
Epithelial-mesenchymal interactions are major driving forces for the development of most solid organs. The importance of these interactions was first shown for the embryonic submandibular gland more than 40 years ago. We here present evidence that interactions between two basement membrane components, nidogen (entactin) and laminin γ1 chain, could be important for epithelial-mes-enchymal interactions in this gland. Nidogen mRNA was detected by in situ hybridization in the mesenchyme, and yet the protein was detected in epithelial and endothelial basement membranes. The role of nidogen-laminin interactions for epithelial morphogenesis was studied by applying antibodies to submandibular gland organ cultures. Antibodies reacting strongly with the nidogen-binding site of laminin γ1 chain drastically perturbed branching epithelial morphogenesis. Electron microscopy of the epithelial-mesenchymal interface showed that blocking antibodies disrupted the formation of the basement membrane. Epidermal growth factor was shown to increase the expression of nidogen in mesenchyme, and could counteract the effect of the blocking antibodies. We suggest that nidogen could be an important mesenchymal factor for submandibular gland development.
Altered cellular proliferation and mesoderm patterning in Polycomb-M33-deficient mice
Authors: Coré Nathalie , Bel Sophie , Gaunt Stephen J. , Aurrand-Lions Michel , Pearce Jonathan , Fisher Amanda , Djabali Malek 
Published: April 2021

ABSTRACT
In Drosophila, the trithorax-group and the Polycomb-group genes are necessary to maintain the expression of the homeobox genes in the appropriate segments. Loss-of-function mutations in those groups of genes lead to misexpression of the homeotic genes resulting in segmental homeotic transformations. Recently, mouse homologues of the Polycomb-group genes were identified including M33, the murine counterpart of Polycomb. In this report, M33 was targeted in mice by homologous recombination in embryonic stem (ES) cells to assess its function during development. Homozygous M33 (−/−) mice show greatly retarded growth, homeotic transformations of the axial skeleton, sternal and limb malformations and a failure to expand in vitro of several cell types including lymphocytes and fibroblasts. In addition, M33 null mutant mice show an aggravation of the skeletal malformations when treated to RA at embryonic day 7.5, leading to the hypothesis that, during development, the M33 gene might play a role in defining access to retinoic acid response elements localised in the regulatory regions of several Hox genes.
The C. elegans MEX-1 protein is present in germline blastomeres and is a P granule component
Authors: Guedes Susana , Priess James R. 
Published: April 2021

ABSTRACT
In the nematode Caenorhabditis elegans, germ cells arise from early embryonic cells called germline blastomeres. Cytoplasmic structures called P granules are present in the fertilized egg and are segregated into each of the germline blastomeres during the first few cleavages of the embryo. Mutations in the maternally expressed gene mex-1 disrupt the segregation of P granules, prevent the formation of germ cells, and cause inappropriate patterns of somatic cell differentiation. We have cloned the mex-1 gene and determined the distribution pattern of the mex-1 gene products. The MEX-1 protein contains two copies of an unusual ‘finger’ domain also found in the PIE-1 protein of C. elegans. PIE-1 has been shown to be expressed in germline blastomeres, and is a component of P granules. We show here that MEX-1 also is present in germline blastomeres and is a P granule component, although MEX-1 is a cytoplasmic protein while PIE-1 is present in both the nucleus and cytoplasm. We further show that MEX-1 is required to restrict PIE-1 expression and activity to the germline blastomeres during the early embryonic cleavages.
The Drosophila mushroom body is a quadruple structure of clonal units each of which contains a virtually identical set of neurones and glial cells
Authors: Ito Kei , Awano Wakae , Suzuki Kazumi , Hiromi Yasushi , Yamamoto Daisuke 
Published: April 2021

ABSTRACT
The mushroom body (MB) is an important centre for higher order sensory integration and learning in insects. To analyse the development and organisation of the MB neuropile in Drosophila, we performed cell lineage analysis in the adult brain with a new technique that combines the Flippase (flp)/FRT system and the GAL4/UAS system. We showed that the four mushroom body neuroblasts (MBNbs) give birth exclusively to the neurones and glial cells of the MB, and that each of the four MBNb clones contributes to the entire MB structure. The expression patterns of 19 GAL4 enhancer-trap strains that mark various subsets of MB cells revealed overlapping cell types in all four of the MBNb lineages. Partial ablation of MBNbs using hydroxyurea showed that each of the four neuroblasts autonomously generates the entire repertoire of the known MB substructures.
Fibroblast growth factors are necessary for neural retina but not pigmented epithelium differentiation in chick embryos
Authors: Pittack Catrin , Grunwald Gerald B. , Reh Thomas A. 
Published: April 2021

ABSTRACT
During eye development, optic vesicles evaginate laterally from the neural tube and develop into two bilayered eye cups that are composed of an outer pigment epithelium layer and an inner neural retina layer. Despite their similar embryonic origin, the pigment epithelium and neural retina differentiate into two very distinct tissues. Previous studies have demonstrated that the developmental potential of the pigmented epithelial cells is not completely restricted; until embryonic day 4.5 in chick embryos, the cells are able to switch their phenotype and differentiate into neural retina when treated with fibroblast growth factors (FGF) (Park, C. M., and Hollenberg, M. J. (1989). Dev. Biol. 134, 201-205; Pittack, C., Jones, M., and Reh, T. A. (1991). Development 113, 577-588; Guillemot, F. and Cepko, C. L. (1992). Development 114, 743-754). These studies motivated us to test whether FGF is necessary for neural retina differentiation during the initial stages of eye cup development. Optic vesicles from embryonic day 1.5 chick were cultured for 24 hours as explants in the presence of FGF or neutralizing antibodies to FGF2. The cultured optic vesicles formed eye cups that contained a lens vesicle, neural retina and pigmented epithelium, based on morphology and expression of neural and pigmented epithelium-specific antigens. Addition of FGF to the optic vesicles caused the presumptive pigmented epithelium to undergo neuronal differentiation and, as a consequence, a double retina was formed. By contrast, neutralizing antibodies to FGF2 blocked neural differentiation in the presumptive neural retina, without affecting pigmented epithelial cell differentiation. These data, along with evidence for expression of several FGF family members and their receptors in the developing eye, indicate that members of the FGF family may be required for establishing the distinction between the neural retina and pigmented epithelium in the optic vesicle.
A Xenopus type I activin receptor mediates mesodermal but not neural specification during embryogenesis
Authors: Chang Chenbei , Wilson Paul A. , Mathews Lawrence S. , Hemmati-Brivanlou Ali 
Published: April 2021

ABSTRACT
Activins and other ligands in the TGFb superfamily signal through a heteromeric complex of receptors. Disruption of signaling by a truncated type II activin receptor, XActRIIB (previously called XAR1), blocks mesoderm induction and promotes neuralization in Xenopus embryos. We report the cloning and characterization of a type I activin receptor, XALK4. Like truncated XActRIIB, a truncated mutant (tXALK4) blocks mesoderm formation both in vitro and in vivo; moreover, an active form of the receptor induces mesoderm in a ligand-independent manner. Unlike truncated XActRIIB, however, tXALK4 does not induce neural tissue. This difference is explained by the finding that tXALK4 does not block BMP4-mediated epidermal specification, while truncated XActRIIB inhibits all BMP4 responses in embryonic explants. Thus, the type I and type II activin receptors are involved in overlapping but distinct sets of embryonic signaling events.
The embryonic cerebellum contains topographic cues that guide developing inferior olivary axons
Authors: Chédotal Alain , Bloch-Gallego Evelyne , Sotelo Constantino 
Published: April 2021

ABSTRACT
The formation of the olivocerebellar projection is supposed to be regulated by positional information shared between pre- and postsynaptic neurons. However, experimental evidence to support this hypothesis is missing. In the chick, caudal neurons in the inferior olive project to the anterior cerebellum and rostral ones to the posterior cerebellum. We here report in vitro experiments that strongly support the existence of anteroposterior polarity cues in the embryonic cerebellum.
We developed an in vitro system that was easily accessible to experimental manipulations. Large hindbrain explants of E7.5-E8 chick embryos, containing the cerebellum and its attached brainstem, were plated and studied using axonal tracing methods. In these cultures, we have shown that the normal anteroposterior topography of the olivocerebellar projection was acquired, even when the cerebellar lamella was detached from the brainstem and placed again in its original position. We also found that, following various experimental rotations of the anteroposterior axis of the cerebellum, the rostromedian olivary neurons still project to the posterior vermis and the caudolateral neurons to the anterior vermis, that now have inverted locations. Thus, the rotation of the target region results in the rotation of the projection. In addition, we have shown that the formation of the projection map could be due to the inability of rostromedian inferior olivary axons to grow in the anterior cerebellum. All these experiments strongly indicate that olivocerebellar fibers recognize within their target region polarity cues that organize their anteroposterior topography, and we suggest that Purkinje cells might carry these cues.
GATA-2 and GATA-3 regulate trophoblast-specific gene expression in vivo
Authors: Ma Grace T. , Roth Matthew E. , Groskopf John C. , Tsai Fong-Ying , Orkin Stuart H. , Grosveld Frank , Engel James Douglas , Linzer Daniel I. H. 
Published: April 2021

ABSTRACT
We previously demonstrated that the zinc finger transcription factors GATA-2 and GATA-3 are expressed in trophoblast giant cells and that they regulate transcription from the mouse placental lactogen I gene promoter in a transfected trophoblast cell line. We present evidence here that both of these factors regulate transcription of the placental lactogen I gene, as well as the related proliferin gene, in trophoblast giant cells in vivo. Placentas lacking GATA-3 accumulate placental lactogen I and proliferin mRNAs to a level 50% below that reached in the wild-type placenta. Mutation of the GATA-2 gene had a similar effect on placental lactogen I expression, but led to a markedly greater reduction (5- to 6-fold) in proliferin gene expression. Placentas lacking GATA-2 secrete significantly less angiogenic activity than wild-type placentas as measured in an endothelial cell migration assay, consistent with a reduction in expression of the angiogenic hormone proliferin. Furthermore, within the same uterus the decidual tissue adjacent to mutant placentas displays markedly reduced neovascularization compared to the decidual tissue next to wild-type placentas. These results indicate that GATA-2 and GATA-3 are important in vivo regulators of trophoblast-specific gene expression and placental function, and reveal a difference in the effect of these two factors in regulating the synthesis of related placental hormones.
Induction of deep layer cortical neurons in vitro
Authors: Bohner Amy P. , Akers Rebecca M. , McConnell Susan K. 
Published: April 2021

ABSTRACT
Transplantation studies suggest that the laminar fates of cerebral cortical neurons are determined by environmental signals encountered just before mitosis. In ferret, E29 progenitor cells normally produce neurons of layers 5 and 6. When transplanted during S-phase into an older ventricular zone, E29 progenitors produce neurons that change their fates and migrate to layer 2/3; however, cells transplanted later in the cell cycle migrate to their normal deep-layer positions even in an older environment (McConnell and Kaznowski, 1991). Here we utilize three culture systems to investigate the nature of the environmental signals involved in laminar specification. E29 cells were first cultured at low density to ascertain whether cell contact and/or short-range cues are required for deep layer specification. Neurons transplanted after a short time in low-density culture failed to adopt their normal fates and migrated instead to the upper layers. When crude cell contacts were restored by pelleting E29 cells together, most transplanted neurons cells became specified to their normal deep layer fates. Finally, E29 cells were transplanted after being cultured in explants that maintained the architecture of the cerebral wall. Explants allowed normal deep layer specification to occur, as transplanted cells migrated to layers 5 and 6. These results suggest that short-range cues induce multipotent progenitors to produce deep layer neurons.