pinecone/core-2020-05-10-deduplication huggingface dataset:
Zebrafish Nodal-Related Genes Are Implicated in Axial Patterning and Establishing Left–Right Asymmetry

AbstractNodal-related 1 (ndr1)andnodal-related 2 (ndr2)genes in zebrafish encode members of the nodal subgroup of the transforming growth factor-β superfamily. We report the expression patterns and functional characteristics of these factors, implicating them in the establishment of dorsal–ventral polarity and left–right asymmetry.Ndr1is expressed maternally, andndr1andndr2are expressed during blastula stage in the blastoderm margin. During gastrulation,ndrexpression subdivides the shield into two domains: a small group of noninvoluting cells, the dorsal forerunner cells, expressndr1,whilendr2RNA is found in the hypoblast layer of the shield and later in notochord, prechordal plate, and overlying anterior neurectoderm. During somitogenesis,ndr2is expressed asymmetrically in the lateral plate as are nodal-related genes of other organisms, and in a small domain in the left diencephalon, providing the first observation of asymmetric gene expression in the embryonic forebrain. RNA injections intoXenopusanimal caps showed that Ndr1 acts as a mesoderm inducer, whereas Ndr2 is an efficient neural but very inefficient mesoderm inducer. We suggest that Ndr1 has a role in mesoderm induction, while Ndr2 is involved in subsequent specification and patterning of the nervous system and establishment of laterality
Localization and Regulation of MuSK at the Neuromuscular Junction

AbstractThe receptor tyrosine kinase, MuSK, is required for the formation of the neuromuscular junction (NMJ) where MuSK becomes phosphorylated when exposed to neuronally synthesized isoforms of agrin. To understand better the mechanisms by which MuSK mediates the formation of the NMJ, we have examined how MuSK expression is regulated during development in the embryo, by neuromuscular injury in the adult and by agrinin vitro.Here we show that MuSK is associated with the earliest observable AChR clusters at the developing motor endplate and that MuSK and AChRs codistribute throughout the development of the NMJ. These two proteins are also coordinately regulated on the surfaces of cultured myotubes where MuSK and AChRs colocalize both in spontaneous and agrin-induced clusters. While MuSK is normally restricted to the motor endplate in adult muscle, denervation results in its extrajunctional expression, although a discernible concentration of MuSK remains localized to the motor endplate even 14 days after denervation. Extrajunctional MuSK is first apparent 3 days after denervation and is sharply reduced upon reinnervation. Muscle paralysis also markedly alters the expression of MuSK in adult muscle and results in increased expression of MuSK as well as increased transcription of MuSK mRNA by extrasynaptic myonuclei. Together, these findings demonstrate that MuSK expression is highly regulated by innervation, muscle activity, and agrin, while the distribution of MuSK is precisely coordinated with that of the AChR
Defect in the Maintenance of the Apical Ectodermal Ridge in theDactylaplasiaMouse

AbstractDuring vertebrate limb development the distal apex of the limb bud ectoderm is induced to form the apical ectodermal ridge (AER). The presence of the AER is required for the continued outgrowth of the limb bud. Classical embryological studies have led to the hypothesis that a secreted mesenchymal factor is required to maintain the AER. We have undertaken a detailed analysis ofDactylaplasia(Dac) mice, a semidominant mutant which displays missing central digits in the fore- and hindlimbs of heterozygous animals and monodactyly in homozygous animals. Our data show thatDacmice have a defect in the maintenance of the AER. At E10.5, the mutant AER is found to be morphologically normal. However, by E11.5 the central aspect of the AER degenerates leaving the anterior and posterior AER intact. In homozygous mice both the central and anterior AER degenerate, while the posterior extremity of the AER is unaffected. Analysis of BrdU incorporation reveals that degeneration of the AER is due to a lack of cell proliferation in the mutant AER. The loss of the AER leads to a reduction in cell proliferation in the subridge mesenchyme at E11.5. The data represent direct genetic evidence for the existence of an AER maintenance activity that is distinct from AER induction and differentiation. Moreover, the data suggest that the role of the AER maintenance factor is to promote cell proliferation in the ridge. Based on our findings, we propose a model for AER maintenance in the vertebrate limb
The Genetic Sequence of Retinal Development in the Ciliary Margin of theXenopusEye

AbstractThe ciliary marginal zone is a perpetually self-renewing proliferative neuroepithelium at the perimeter of the retina in amphibians and fish. In the ciliary marginal zone (CMZ), cells are spatially ordered with respect to cellular development, deep stem cells being most peripheral and differentiating retinal progenitors being most central. This spatial gradient in the CMZ recapitulates embryonic retinogenesis and provides a powerful system to examine the relative order of gene expression during this process. A number of neurogenic and proneural genes have been described to have interacting roles in the development of the vertebrate nervous system, and so it is of major importance to put these genes in a hierarchical pathway. In no other system yet described are the developmental stages of neurogenesis arrayed so clearly in a spatial pattern as in the CMZ. We have therefore taken advantage of this system, using doublein situhybridizations on cross sections of the CMZ, to compare the spatial patterns of 15 proneural, neurogenic, and other genes involved in early and late phases of retinal development. In addition, we have positioned these expression patterns with respect to cell division. What emerges from this work is a spatial ordering of gene expression that predicts a genetic hierarchy governing vertebrate retinogenesis. By injecting messenger RNA for some of these genes into blastomeres of theXenopusembryo and examining the effects on expression of the putative downstream genes, we have been able to corroborate some of the relationships between genes predicted to act sequentially
Genetic Requirements for PIE-1 Localization and Inhibition of Gene Expression in the Embryonic Germ Lineage ofCaenorhabditis elegans

AbstractIn earlyCaenorhabditis elegansembryos, production of new mRNAs is inhibited in the germ lineage. This inhibition requires the germline factor PIE-1, and correlates with the absence in germline blastomeres of a phosphoepitope on RNA polymerase II (RNAPII-H5). We show that PIE-1 is uniformly distributed in oocytes and newly fertilized eggs, and becomes localized asymmetrically in the late one-cell stage. To begin to dissect the mechanisms required for PIE-1 localization and inhibition of RNAPII-H5 expression, we have examined the distribution of PIE-1 and RNAPII-H5 in maternal-effect mutants that disrupt embryonic development. We find that mutants that disrupt the asymmetric divisions of germline blastomeres mislocalize PIE-1, and activate RNAPII-H5 expression in the germ lineage. In contrast, mutants that alter somatic cell identities do not affect PIE-1 localization or RNAPII-H5 expression. Our observations suggest that PIE-1 represses mRNA transcription in each germline blastomere in a concentration-dependent manner. We also show that in wild-type, and in mutants where PIE-1 is mislocalized, the cellular and subcellular distribution of PIE-1 remarkably parallels that of the P granules, suggesting that the localizations of these two germline components are coordinately regulated
Requirement for the Vasa RNA Helicase ingurkenmRNA Localization

AbstractLocalization of specific mRNAs to distinct sites within theDrosophilaoocyte is an early and key step in establishing the anterior–posterior and dorsal–ventral axes. We describe a new function for the RNA helicase encoded by the “posterior” group genevasa(vas) in control of localization of the mRNA encoded by the “dorsal–ventral” patterning genegurken(grk). Two new ethyl methane sulfonate-induced, female sterile alleles ofvashave been isolated. In these mutantsgrkmRNA fails to become localized properly and GRK protein is barely detectable. Surprisinglyfs(1)K10, a recessive female sterile mutation that results in mislocalization ofGRKmRNA to the anterior end of the oocyte, is epistatic to thesevasalleles. This result demonstrates that GRK protein levels sufficient to dorsalize the egg chamber can accumulate invasmutants, iffs(1)K10is also mutant. Taken together these results suggest that regulation ofGRKmRNA localization normally occurs, directly or indirectly, through the VAS RNA-dependent RNA helicase and may suggest that accumulation of GRK protein normally depends onGRKmRNA localization
Isolation of the Rat Spermatid Manchette and Its Perinuclear Ring

AbstractThe manchette is a transient structure that develops during spermiogenesis. It consists of three components: a perinuclear ring, a microtubule mantle inserted in the ring, and dense plaques attached at the distal end of the mantle. A procedure has been developed for the fractionation of intact manchettes from rat spermatids. Each fractionation step was monitored by indirect immunofluorescence using an antibody to unmodified α-tubulin. Indirect immunofluorescence and electron microscopy demonstrate that fractionated manchettes are relatively intact. A thermocleavage step was used to sever the microtubule mantle from the perinuclear ring. Microtubules of the mantle collected in a stabilizing buffer containing Taxol formed long bundles of side-by-side aligned microtubules. The perinuclear ring sample consisted of circular-shaped units of different diameter with truncated microtubules still attached to the ring, a property that enabled the initial recognition of the rings by α-tubulin antibody staining. Indirect immunofluorescence and immunoblotting experiments using isoform-specific antibodies to α-tubulins show that the manchette contains acetylated, tyrosinated, glutamylated α-tubulin and an α-3/7 tubulin isoform. The same α-tubulin isoforms were observed in the axoneme of the sperm tail. Two-dimensional polyacrylamide gel electrophoresis fractionation maps of silver-stained proteins of the intact manchette show four predominant proteins: α- and β-tubulins, β-actin, vimentin, and a 62-kDa protein. The latter persisted in thermocleaved perinuclear ring samples. Results of this study indicate that the newly developed procedure for the fractionation of manchettes will facilitate a direct characterization of posttranslationally modified tubulin variants, microtubule-associatedproteins, and the components of the perinuclear ring of this largely neglected structure of the spermiogenic process
Sea Urchin FGFR Muscle-Specific Expression: Posttranscriptional Regulation in Embryos and Adults

AbstractWe have shown previously byin situhybridization that a gene encoding a fibroblast growth factor receptor (SpFGFR) is transcribed in many cell types during the initial phases of sea urchin embryogenesis (Strongylocentrotus purpuratus) (McCoonet al., J. Biol. Chem. 271,20119–20195, 1996). Here we demonstrate by immunostaining with affinity-purified antibody that SpFGFR protein is detectable only in muscle cells of the embryo and appears at a time suggesting that its function is not in commitment to a muscle fate, but instead may be required to support the proliferation, migration, and/or differentiation of myoblasts. Surprisingly, we find thatSpFGFRtranscripts are enriched in embryo nuclei, suggesting that lack of processing and/or cytoplasmic transport in nonmuscle cells is at least part of the posttranscriptional regulatory mechanism. Western blots show that SpFGFR is also specifically expressed in adult lantern muscle, but is not detectable in other smooth muscle-containing tissues, including tube foot and intestine, or in coelomocytes, despite the presence ofSpFGFRtranscripts at similar concentrations in all these tissues. We conclude that in both embryos and adults, muscle-specific SpFGF receptor synthesis is controlled primarily at a posttranscriptional level. We show by RNase protection assays that transcripts encoding the IgS variant of the ligand binding domain of the receptor, previously shown to be enriched in embryo endomesoderm fractions, are the predominant, if not exclusive,SpFGFRtranscripts in lantern muscle. Together, these results suggest that only a minority ofSpFGFRtranscripts are processed, exported, and translated in both adult and embryonic muscle cells and these contain predominantly, if not exclusively, IgS ligand binding domain sequences
Multiple Roles forNotchinDrosophilaMyogenesis

AbstractNotchplays a role in many cell fate decisions in the developingDrosophilaembryo, often at successive stages during the formation of a single tissue. In the embryonic mesoderm,Notchis involved in the process by which muscle progenitors are selected from a field of equivalent myoblasts. We have investigated the roles ofNotchin somatic myogenesis and show thatNotchcan affect at least two additional steps in muscle development. Subsequent to the initial specification of progenitors, myoblast identity remains sensitive to mesodermalNotchactivity until the time of fusion. Additionally,Notchis capable of suppressing muscle development nonautonomously by regulating a signal that emanates from the ectoderm
Morphogenesis of Digits in the Avian Limb Is Controlled by FGFs, TGFβs, and Noggin through BMP Signaling

AbstractIn the final stages of limb morphogenesis, autopodial cells leaving the progress zone differentiate into cartilage or undergo apoptotic cell death, depending on whether they are incorporated into the digital rays or interdigital spaces. Most evidence indicates that these two opposite fates of the autopodial mesoderm are controlled by BMP signaling. However, the molecular basis for these two distinct actions of BMPs, including the receptors involved in the process, is controversial. In this study we have addressed this question by exploring the presence in the developing autopod of diffusible signals able to modulate BMP function and by analyzing the effects of their exogenous administration on the pattern of expression of BMP receptor genes. Our findings show thattgfβ2andnoggingenes are expressed in the condensing region of the developing digital rays in addition to the well-known distribution in the autopodial tissues of FGFs (apical ectodermal ridge, AER) and BMPs (AER, progress zone mesoderm, and interdigital regions). Exogenous administration of all the factors causes changes in the expression of thebmpR-1bgene which are followed by parallel alterations of the skeletal phenotype: FGFs inhibit the expression ofbmpR-1bcompatible with their function in the maintenance of the progress zone mesoderm in an undifferentiated state; and TGFβs induce the expression ofbmpR-1band promote ectopic chondrogenesis, compatible with a function in the establishment of the position of the digital rays. In addition we provide evidence for the occurrence of an interactive loop between BMPs and noggin accounting for the spatial distribution ofbmpR-1bwhich may control the size and shape of the skeletal pieces. In contrast to thebmpR-1bgene, thebmpR-1agene is expressed at low levels in the autopodial mesoderm and its expression is not modified by any of the tested factors regardless of their effects on chondrogenesis or cell death. Finally, the role of BMPs in programmed cell death is confirmed here by the intense inhibitory effect of noggin on apoptosis, but the lack of correlation between changes in the pattern of cell death induced by treatment with the studied factors and the expression of eitherbmpR-1aorbmpR-1bgenes suggest that a still-unidentified BMP receptor may account for this BMP function
Centrosome Reduction during Mouse Spermiogenesis

AbstractThe sperm does not contribute the centrosome during murine fertilization. To determine the manner in which a functional centrosome is reduced, we have studied centrosome degeneration during spermiogenesis of mice. The round spermatids display normal centrosomes consisting of a pair of centrioles along with γ-tubulin containing foci. However, they do not seem to organize microtubules. Elongating spermatids display γ-tubulin spots in the neck region, while microtubules are organized from the perinuclear ring as the manchette. Electron microscopic studies using immunogold labeling revealed that γ-tubulin is mainly localized in the centriolar adjunct from which an aster of microtubules emanates. Microtubules repolymerized randomly in the cytoplasm after nocodazole treatment and reversal. γ-Tubulin dissociates from the neck region and is discarded in the residual bodies during spermiation. The distal centriole degenerates during testicular stage of spermiogenesis, while the proximal centriole is lost during epididymal stage. Loss of centrosomal protein and centrioles in mouse sperm further confirm the maternal inheritance of centrosome during murine fertilization
Intercellular Bridges between Epithelial Cells in theDrosophilaOvarian Follicle: A Possible Aid to Localized Signaling

AbstractIn the epithelium ofDrosophilaovarian follicles, cytoplasm-filled intercellular bridges connect epithelial cells. This study presents further descriptive information about the morphology of these intercellular bridges and the extent of their distribution. We also offer speculations concerning the possible developmental importance of the epithelial bridges. These bridges, whose luminal diameters averaged 0.25 μm, are smaller than those forming the ring canals joining germline cells: nor do they increase their size over time. The membranes limiting the bridges are lined on the cytoplasmic side with an electron-dense material to which is attached a monolayer of filaments which encircle the bridge. By decoration with the S1 fragment of myosin, these filaments are confirmed as actin filaments. Following disruption of gap junctional dye coupling by treatment with 1 mM octanol, microinjection of Lucifer yellow CH revealed the extent and distribution of follicle cell intercellular bridges to be confined to arrays of no more than eight cells/cluster, with many such independent clusters comprising the epithelium. Thus cell-to-cell movement throughout the epithelium of cytosolic regulatory molecules cannot occur via these intercellular bridges. However, weak signals affecting only one or a few cells in each cluster would be amplified throughout the group by spread through the intercellular bridges
The Origin of the Subepicardial Mesenchyme in the Avian Embryo: An Immunohistochemical and Quail–Chick Chimera Study

AbstractIt has been proposed that the subepicardial mesenchymal cells (SEMC) originate from the primitive epicardium and also from migration of extracardiac mesenchyme from the liver area. We have studied the possibility of an origin of SEMC through transformation of the proepicardial mesothelium, as well as the potential of the early proepicardium to generate epicardium and SEMC in quail–chick chimeras. The study was carried out in quail and chick embryos between HH16 and HH29 stages. Most proepicardial cells, mesothelial as well as mesenchymal, were cytokeratin and vimentin immunoreactive, suggesting a cytoskeletal shift from the epithelial to the mesenchymal type. Furthermore, we immunolocated, in the proepicardial mesothelium, three proteins specifically expressed during the endothelial–mesenchymal transition of the endocardial cushions, namely the JB3/fibrillin-associated antigen, the ES/130 protein and the smooth muscle cell α-actin. Grafts of proepicardial tissue from HH16–17 quail embryos into chick embryos of the same age originated large areas of donor-derived epicardium, including mesothelial, mesenchymal, and vascular cells. The donor-derived primitive epicardium showed segment-specific features, being squamous and adhered to the myocardium on the atrial wall and showing morphological signs of ingression in the atrioventricular groove and outflow tract. These morphological traits together with the distribution of vimentin, the ES/130 protein, and the JB3/fibrillin-associated antigen suggested a localized transformation of some epicardial mesothelial cells into mesenchyme. Most of the donor-derived cells, mesothelial and mesenchymal, showed the vascular marker QH1, which frequently colocalized with cytokeratin. Heterotopic grafts of quail splanchnopleura into the pericardial cavity of chick embryos originated a squamous, epicardial-like, cytokeratin-immunoreactive cell layer on the heart surface, as well as a few QH1+subepicardial and intramyocardial cells. The results suggest that a substantial part of the subepicardial mesenchyme, including the progenitors of the cardiac vessels, originates from the transformation of proepicardial and epicardial mesothelial cells into mesenchyme, and that the epicardial transition could be driven by a segment-specific myocardial signal
Evidence That Dorsal–Ventral Differences in Gap Junctional Communication in the EarlyXenopusEmbryo Are Generated by β-Catenin Independent of Cell Adhesion Effects

AbstractGap junctional communication (GJC) is regulated in the earlyXenopusembryo and quantitative differences in junctional communication correlate with the specification of the dorsal–ventral axis. To address the mechanism that is responsible for regulating this differential communication, we investigated the function of β-catenin during the formation of the dorsal–ventral axis inXenopusembryos by blocking its synthesis with antisense oligodeoxynucleotides. This method has previously been shown to reduce the level of β-catenin in the early embryo, prior to zygotic transcription, and to inhibit the formation of the dorsal axis (Heasmanet al., 1994,Cell79, 791–803). We show here that antisense inhibition of β-catenin synthesis also reduces GJC among cells in the dorsal hemisphere of 32-cell embryos to levels similar to those observed among ventral cells. Full-length β-catenin mRNA can restore elevated levels of dorsal GJC when injected into β-catenin-deficient oocytes, demonstrating the specificity of the β-catenin depletion with the antisense oligonucleotides. Thus, endogenous β-catenin is required for the observed differential GJC. This regulation of GJC is the earliest known action of the dorsal regulator, β-catenin, inXenopusdevelopment. Two lines of evidence, presented here, indicate that β-catenin acts within the cytoplasm to regulate GJC, rather than through an effect on cell adhesion. First, when EP-cadherin is overexpressed and increased adhesion is observed, embryos display both a ventralized phenotype and reduced dye transfer. Second, a truncated form of β-catenin (i.e., the ARM region), that lacks the cadherin-binding domain, restores dorsal GJC to β-catenin-depleted embryos. Thus, β-catenin appears to regulate GJC independent of its role in cell–cell adhesion, by acting within the cytoplasm through a signaling mechanism