pinecone/core-2020-05-10-deduplication huggingface dataset:
A Role fornautilusin the Differentiation of Muscle Precursors

AbstractIn theDrosophilaembryo,nautilusis expressed in a subset of muscle precursors and differentiated fibers and is capable of inducing muscle-specific transcription, as well as myogenic transformation. In this study, we examine the consequences ofnautilusloss-of-function on the development of the somatic musculature. Genetic and molecular characterization of two overlapping deficiencies,Df(3R)nau-9andDf(3R)nau-11a4,revealed that both of these deficiencies remove thenautilusgene without affecting a common lethal complementation group. Individuals transheterozygous for these deficiencies survive to adulthood, indicating thatnautilusis not an essential gene. These embryos are, however, missing a subset of muscle fibers, providing evidence that (1) some muscle loss can be tolerated throughout larval development and (2)nautilusdoes play a role in muscle development. Examination of muscle precursors in these embryos revealed thatnautilusis not required for the formation of muscle precursors, but rather plays a role in their differentiation into mature muscle fibers. Thus, we suggest thatnautilusfunctions in a subset of muscle precursors to implement their specific differentiation programs
Experimental Induction ofBMP-4Expression Leads to Apoptosis in the Paraxial and Lateral Plate Mesoderm

AbstractIn the avian embryo, epithelialization of the segmental plate and formation of an epithelial dermomyotome depend on signals from the neural tube and the ectoderm overlying the paraxial mesoderm. In this study, we report that ectoderm removal in combination with barrier insertion between the axial organs and the segmental plate leads to an induction ofBMP-4expression in the paraxial mesoderm. In the lateral plate, ectoderm removal alone leads to an increase ofBMP-4expression. Application of BMP-4 protein results in a lack of epithelialization of the paraxial mesoderm. In order to investigate whether the loss of epithelial structures after these manipulations can be attributed to a change in cell fate, a change in cell proliferation, or the induction of apoptosis, the paraxial mesoderm was tested for expression ofMsx-2, BMP-2, BMP-4,andBMP-7.Moreover, BrdU and TUNEL staining were carried out. The inhibition of epithelialization after ectoderm removal alone and after segregation of the axial organs is accompanied neither by an increase in apoptosis nor by a reduction of the proliferation rate in the paraxial mesoderm. On the other hand, an ectopicBMP-4expression in the paraxial mesoderm after ectoderm removal in combination with barrier insertion coincides with the occurrence of apoptotic cells and reduction of proliferation rate in this tissue. Increase of apoptosis and decrease in cell proliferation are observed in the paraxial and lateral plate mesoderm also after application of BMP-4 protein
Tissues Exhibiting Inhibiory and Repulsive Activities during the Initial Stages of Neurite Outgrowth from the Dorsal Root Ganglion in the Chick Embryo

AbstractTo elucidate the mechanisms underlying the projection of dorsal root ganglion (DRG) axons into the dorsal root entry zone in the dorsolateral region of the spinal cord, we examined tissue interactions which affect neurite outgrowth from DRG. We cultured explants or dissociated cells of DRG from embryonic day 4 (E4) chick embryos in combination with E3 spinal cord, notochord, and dermomyotome in three-dimensional collagen gels. The ventral spinal cord, notochord, and dermomyotome, which are located close to the initial projection pathway of DRG but do not receive direct innervation, strongly inhibited DRG neurite outgrowth and repelled DRG neurites. These inhibitory/repulsive cues appear diffusible in nature, because this activity was observed in the absence of direct contacts between tissue explants and DRG neurites. Furthermore, in heterochronic cultures, E9 DRG lost its responsiveness to inhibitory/repulsive factors from E3 ventral spinal cord, while retaining responsiveness to E3 notochord and dermomyotome, suggesting that the E3 ventral spinal cord may secrete a different inhibitory/repulsive signal than notochord and dermomyotome. Putative inhibitory/repulsive signals secreted from tissues along the axonal pathway may serve to guide growing DRG axons to the dorsal root entry zone
Glycosylphosphatidylinositol-Anchored Cell Surface Proteins Regulate Position-Specific Cell Affinity in the Limb Bud

AbstractAlthough regional differences in mesenchymal cell affinity in the limb bud represent positional identity, the molecular basis for cell affinity is poorly understood. We found that treatment of the cell surface with bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) could change cell affinity in culture. When PI-PLC was added to the culture medium, segregation of the progress zone (PZ) cells from different stage limb buds was inhibited. Similarly, sorting out of the cells from different positions along the proximodistal (PD) axis of the same stage limb buds was disturbed. Since PI-PLC can remove glycosylphosphatidylinositol (GPI)-anchored membrane bound proteins from the cell surface, the GPI-anchored cell surface proteins may be involved in sorting out. To define the GPI-anchored molecules that determine the segregation of limb mesenchymal cells, we examined the effect of neutralizing antibody on the EphA4 receptor that binds to GPI-anchored cell surface ligands, called ephrin-A. Sorting out of the PZ cells at different stages could be inhibited by the neutralizing antibody to EphA4. These results suggest that EphA4 and its GPI-anchored ligands are, at least in part, involved in sorting out of limb mesenchymal cells with different proximal–distal positional values, and that GPI-anchored cell surface proteins play important roles in determining cell affinity in the limb bud
Mastermind Acts Downstream of Notch to Specify Neuronal Cell Fates in theDrosophilaCentral Nervous System

AbstractIn theDrosophilacentral nervous system, cellular diversity is generated through the asymmetric partitioning of cell fate determinants at cell division. Neural precursors (or neuroblasts) divide in a stem cell lineage to generate a series of ganglion mother cells, each of which divides once to produce a pair of postmitotic neurons or glial cells. An exception to this rule is the MP2 neuroblast, which divides only once to generate two neurons. We screened for genes expressed in the MP2 neuroblast and its progeny as a means of identifying the factors that specify cell fate in the MP2 lineage. We identified a P-element insertion line that expresses the reporter gene, tau-β-galactosidase, in the MP2 precursor and its progeny, the vMP2 and dMP2 neurons. The transposon disrupts the neurogenic gene,mastermind,but does not lead to neural hyperplasia. However, the vMP2 neuron is transformed into its sibling cell, dMP2. By contrast, expression of a dominant activated form of the Notch receptor in the MP2 lineage transforms dMP2 to vMP2. Notch signalling requires Mastermind, suggesting that Mastermind acts downstream of Notch to determine the vMP2 cell fate. We show that Mastermind plays a similar role in the neurons derived from ganglion mother cells 1-1a and 4-2a, where it specifies the pCC and RP2sib fates, respectively. This suggests that Notch signalling through Mastermind plays a wider role in specifying neuronal identity in theDrosophilacentral nervous system
The 350-kDa Sea Urchin Egg Receptor for Sperm Is Localized in the Vitelline Layer

AbstractPrevious studies have established by several methods that the 350-kDa egg receptor for sperm is localized on the plasma membrane–vitelline layer complex of the egg of the sea urchinStrongylocentrotus purpuratus.In addition, it has been found that molecules which are cross-reactive with anti-receptor antibody are present in the cortical granules located at the inner face of the plasma membrane. The objective of this study was to define more precisely the locale of the cell surface receptor. We have found that following fertilization, the immunoreactive receptor initially found on the egg surface moved to the fertilization envelope (FE) and then disappeared in parallel with the loss of sperm binding activity. A cross-linked, high-molecular-weight derivative of soybean trypsin inhibitor (hMW-SBTI) which was unable to pass through the elevating FE blocked the loss of both immunoreactivity and the sperm binding activity of the FE, but did not inhibit the vitelline delaminase activity that has been implicated in FE formation. Western blot analysis following SDS–PAGE of the proteins of the FE isolated in the presence of hMW-SBTI and benzamidine revealed the presence of the 350/320-kDa proteins which cross-reacted with anti-receptor antibody. Experiments in which molecules on the surface of unfertilized eggs were labeled with biotin and traced after FE formation revealed that a significant portion of the 350/320-kDa glycoproteins that were incorporated into the FE originated from the cell surface, rather than from the cortical granules. These findings provide strong evidence that in unfertilized eggs the egg receptor for sperm exists as part of the protein complex known as the vitelline layer which serves as a precursor of the FE. Evidence is presented indicating that some of the receptor in the vitelline layer is cryptic and a possible function for this cryptic form of the receptor is proposed
The Shaping of Pharyngeal Cartilages during Early Development of the Zebrafish

AbstractIn zebrafish the cartilages of the pharynx develop during late embryogenesis and grow extensively in the larva before eventually being replaced by bone. Here we examine chondrocyte arrangements, shapes, numbers, and divisions in the young hyoid cartilages. We observe two distinct developmental phases, morphogenesis and growth. The first phase generates stereotypically oriented chondrocyte stacks that might form by intercalations among cells within the precartilage condensations. In mutants that have deformed cartilages the orientation of the stacks is changed, and we propose that their correct formation underlies the correct initial shaping of the organ. The following period of rapid, nearly isometric cartilage growth occurs by divisions of chondrocytes that are largely located near the joints, and appears to be under quite separate regulation
Neural Crest-Specific and General Expression of Distinct Metalloprotease–Disintegrins in EarlyXenopus laevisDevelopment

AbstractMetalloprotease–disintegrins are a family of membrane-anchored glycoproteins that have been implicated in diverse cellular processes, including fertilization and myoblast fusion, release of TNFα from the plasma membrane, and neurogenesis. Here we report the cloning of cDNAs encoding three full-length (xMDC9, xMDC11b, and xMDC13), and one partial (xMDC11a) metalloprotease–disintegrin from the amphibianXenopus laevis,and the analysis of their expression during earlyX. laevisdevelopment and in adult tissues. The most notable finding was the highly localized and specific expression pattern ofxmdc11aat the tailbud stage in the cranial neural crest and in a subset of neural tube cells in the trunk region. In contrast, expression of the closely relatedxmdc11bwas not detectable during the early stages ofX. laevisdevelopment, and remained low in the adult tissues examined here. Distinct expression patterns were also observed for two other highly relatedX. laevisgenes,xmdc13andadam13(Alfandariet al.,1997). Whileadam13is expressed in the somitic mesoderm and in neural crest cells, but not in adult testis,xmdc13expression is low and ubiquitous in the developing embryo, but is clearly present in adult testis. Finally,xmdc9,the putative orthologue of human and mousemdc9,was found at all stages of development, and in all tissues examined, suggesting a function that may be utilized by most or all cells. The noteworthy features of these fourxmdcgenes and the implications of their distinct spatial and temporal expression patterns are discussed
Development of the Avian Iris and Ciliary Body: Mechanisms of Cellular Differentiation during the Smooth-to-Striated Muscle Transition

AbstractThe avian iris and ciliary body undergoes a transition from smooth-to-striated muscle during embryonic development. Using antibodies specific for smooth muscle-specific α-actin and myosin heavy chain, we confirm that a smooth-to-striated muscle transition occurs between E8 and E17 in both iris and ciliary body of the chick. To study the mechanisms regulating the transition in muscle type, we analyzed the fate of quail clones derived from E7 iris cells. When cells were cloned alone, 45/71 colonies differentiated into smooth muscle and 10/71 became striated muscle. None of the colonies were mixed with respect to muscle phenotype, indicating a lack of pluripotent stem cells. Furthermore, clones giving rise to nonstriated muscle could not be forced to incorporate into myotubes when cocultured with chick myocytes. Clones grown in coculture with chick embryo fibroblasts or E11 iris cells had very high cloning efficiencies (>98%). Significantly more clones differentiated into striated muscle when cocultured with E11 cells (60/156) than when cocultured with fibroblasts (29/108). This was due to an increased recruitment of undifferentiated cells into striated muscle, rather than a change in the percentage of cells differentiating into smooth muscle.In vivoandin vitro,various smooth and striated muscle-specific markers including contractile proteins, acetylcholine receptor subtypes, and transcription factors were colocalized in cells. Although our data argue against a multipotent stem cell for smooth and striated muscle cells, they cannot exclude a role for transdifferentiation. Cumulatively these results suggest that both smooth muscle and migratory myoblasts contribute to the development of myotubes in the avian iris and that this process is regulated in a non-cell-autonomous fashion by locally generated signals
Inhibition of Phosphoinositide Metabolism or Chelation of Intracellular Calcium Blocks FSH-Induced but Not Spontaneous Meiotic Resumption in Mouse Oocytes

AbstractMammalian oocytes are arrested at the diplotene phase of the first meiotic division until ovulation. In the mouse, germinal vesicle breakdown (GVBD) and progression to metaphase II is thought to be triggered by a positive signal originating in the follicular cells following stimulation by the luteinizing hormone (LH) surge. Isolated, fully grown oocytes can also undergo spontaneous reinitiation of meiosisin vitroin the absence of gonadotrophin stimulation. To investigate the mechanism of meiotic resumption, inhibitors of phosphoinositide metabolism and an intracellular calcium chelator were used during maturationin vitrounder different conditions. In a series of experiments, isolated cumulus cell–oocyte complexes (COCs) maintained in meiotic arrest by hypoxanthine were induced to resume meiosis by treatment with follicle-stimulating hormone (FSH). Under these conditions, both LiCl and neomycin, which inhibit phosphoinositide hydrolysis, produced a dose-dependent inhibitory effect on meiotic resumption. Similar results were obtained when FSH-induced meiotic resumption was observed in the presence of the acetoxymethyl ester form of 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA/AM), an intracellular calcium chelator. In hypoxanthine-arrested oocytes, GVBD induced by epidermal growth factor (EGF), which mimics FSH action inin vitromaturation, was also repressed by LiCl and neomycin. Conversely, meiotic resumption triggered by a pulse of 8-bromo-cyclic adenosine monophosphate (8-Br cAMP) was not affected by these two inhibitors. In experiments in which oocytes were cultured under conditions which permit spontaneous meiotic maturation, resumption of meiosis was not affected by either inhibition of phosphoinositide hydrolysis or chelation of intracellular calcium. Therefore, it appears that meiotic resumption induced by hormone stimulation requires activation of the phosphoinositide pathway and mobilization of intracellular calcium. In contrast, spontaneous maturation probably occurs through a different mechanism because it is not affected by inhibition of this signaling pathway
spadetail-Dependent Cell Compaction of the Dorsal Zebrafish Blastula

AbstractThe dorsal marginal zone of the zebrafish blastula, equivalent to the amphibian Spemann organizer, is destined to become the tissues of the notochord and prechordal plate. Preceding gastrulation in the zebrafish, we find that these future mesendodermal cells acquire a cohesive cell behavior characterized by flattening and maximization of intercellular contacts, somewhat resembling cell compaction in mouse blastocysts. This behavior may suppress cell intermingling. Surprisingly, this blastula cell compaction requires normal function ofspadetail,a gene known to be necessary for the dorsal convergent cell movement of paraxial mesoderm later in the gastrula. We propose thatspadetail-dependent cell compaction subtly controls the early mixing and dispersal of dorsal cells that coalesce into the prospective organizer region. This early process may be necessary for the correct location of the boundary separating axial and paraxial cells
Regionalized Organizing Activity of the Neural Tube Revealed by the Regulation of lmx1 in the Otic Vesicle

AbstractLIM homeodomain genes have been involved in patterning in a variety of organisms. I have analyzed the expression of lmx1 during early ear development and explored its regulation by the neuroectoderm. Experiments were carried out on chick embryos. During early somitic stages (4–6 somites), lmx1 was expressed in the neural tube and in a stripe of the dorsal ectoderm. The ectodermal expression domain was then restricted to the otic placode (7–10 somites). At otic cup stages, lmx1 was downregulated in ventral and medial aspects of the otic epithelium facing the neural tube. This resulted in a dorsal and lateral restriction of lmx1 that persisted until the otic vesicle stage. The dependence of lmx1 on interactions with the neuroectoderm was explored by carrying out ablations of the neural tube in organotypic explants containing the otic presumptive ectoderm. Both the formation of the otic vesicle and expression of lmx1 were dependent on the presence of the neural ectoderm during stages preceding placode formation (4–6 somites). Thereafter, the formation of the otic vesicle was progressively autonomous, and by the stage of 10 somites the otic ectoderm developed into otic vesicles and expressed lmx1 in foreign environments. Dorsal and ventral neuroectoderms displayed differential effects on lmx1 expression. Ablation of the dorsal neural tube resulted in a reduced expression of lmx1, which was more dramatic during early placode and preplacode stages (5–7 somites). Removal of the ventral aspect of the neural tube (including the notochord) had opposite effects, expression of lmx1 increased, and its domain expanded. The formation of the otic vesicle, however, was supported by either the dorsal or ventral neuroectoderm. The experiments suggest that lmx1 is involved in early patterning of the otic vesicle, and they provide evidence for the regional segregation of organizing activities within the neural tube
Gap Junctions Are Involved in the Early Generation of Left–Right Asymmetry

AbstractInvariant left–right asymmetry of the visceral organs is a fundamental feature of vertebrate embryogenesis. While a cascade of asymmetrically expressed genes has been described, the embryonic mechanism that orients the left–right axis relative to the dorsoventral and anteroposterior axes (a prerequisite for asymmetric gene expression) is unknown. We propose that this process involves dorsoventral differences in cell–cell communication through gap junctions composed of connexin proteins. Global modulation of gap junctional states inXenopusembryos by pharmacological agents specifically induced heterotaxia involving mirror-image reversals of heart, gut, and gall bladder. Greatest sensitivity was observed between st. 5 and st. 12, well before the onset of organogenesis. Moreover, heterotaxia was also induced following microinjection of dominant negative and wild-type connexin mRNAs to modify the endogenous dorsoventral difference in junctional communication. Heterotaxia was induced by either blocking gap junction communication (GJC) dorsally or by introducing communication ventrally (but not the reverse). Both connexin misexpression and exposure to GJC-modifying drugs altered expression of the normally left-sided geneXNR-1,demonstrating that GJC functions upstream ofXNR-1in the pathway that patterns left–right asymmetry. Finally, lineage analysis to follow the progeny of microinjected cells indicated that they generally do not contribute the asymmetric organs. Together with the early sensitivity window, this suggests that GJC functions as part of a fundamental, early aspect of left–right patterning. In addition, we show that a potential regulatory mutation in Connexin43 is sufficient to cause heterotaxia. Despite uncertainty about the prevalence of the serine364to proline substitution reported in human patients with laterality defects, the mutant protein is both a mild hypomorph and a potent antimorph as determined by the effect of its expression on left–right patterning. Taken together, our data suggest that endogenous dorsoventral differences in GJC within the early embryo are needed to consistently orient left–right asymmetry
N-Cadherin/Catenin-Mediated Morphoregulation of Somite Formation

AbstractSomitogenesis during early stages in the chick and mouse embryo was examined in relation to N-cadherin-mediated adhesion. Previous studies indicated that N-cadherin localizes to the somite regions during their formation. Those observations were extended to include a spatiotemporal immunohistochemical analyses of β-catenin and α-catenin, as well as a more detailed study of N-cadherin, during segmentation, compaction, and compartmentalization of the somite. N-cadherin and the catenins appear early within the segmental plate and are expressed as small patch-like foci throughout this tissue. The small foci of immunostaining coalesce into larger clusters of N-cadherin/catenin-expressing regions. The clusters subsequently coalesce into a region of centrally localized cells that express N-cadherin/catenins at their apical surfaces. The multiple clusters are spaced wide apart in the anterior segmental plates that form the first 6 somite pairs, as contrasted to segmental plates that form somites 7 and beyond. To examine the functional significance of N-cadherin, segmental plates were exposed to antibodies that perturb N-cadherin-mediated adhesion in the chick embryo. The multiple, anomalous somites that result in these experiments indicate that each N-cadherin/catenin-expressing cluster can give rise to a somitic structure. β-Catenin involvement in somitogenesis suggests a role for Wnt-mediated signaling. Embryos treated with LiCl also show induction of similar anomalous somites indicating further the possibility that Wnt-mediated signaling may be involved in the clustering event. It is suggested that β-catenin serves to initiate the adhesion process which is spread then by N-cadherin. Later during compartmentalization, N-cadherin/catenins remain expressed by the myotome compartment. Taken together, these results suggest that the Ca2+-dependent cell adhesion molecule N-cadherin and the intracellular catenins are important in segmentation and formation of the somite and myotome compartment. It is proposed that the N-cadherin-mediated adhesion process may serve as a common, evolutionarily conserved, link in the differentiation pathways of skeletal and cardiac muscle