pinecone/core-2020-05-10-deduplication huggingface dataset:
Distinct and Overlapping Expression Patterns of Ligands for Eph-Related Receptor Tyrosine Kinases during Mouse Embryogenesis

AbstractRecent studies have implicated Eph-related receptor tyrosine kinases and their membrane-bound ligands in restricting or stimulating the movement of cells and axons. Members of these large families of receptors and ligands fall into two major binding specificity classes, in which the GPI-anchored subgroup of ligands can each bind to all members of a subgroup of receptors, whereas the transmembrane ligands interact with a distinct subgroup of receptors. Analysis of expression patterns is therefore important in order to understand which receptor–ligand interactions occurin vivo.We have cloned mouse orthologues of five members of the ligand family and analysed in detail their developmental expression, in comparison with each other, and with the receptor specificity class they can interact with. We find that B61, AL-1/RAGS, LERK4, and ELF-1, members of the GPI-anchored subgroup of ligands, have both distinct and overlapping aspects to their expression in early mesoderm, somites, and branchial arches; in complex, dynamic patterns in the limb; and in spatial domains and specific neurons in the CNS. Similarly, Elk-L is expressed in hindbrain segments, the roof plate, and floor plate, which overlaps with that of other transmembrane ligands, but has distinct expression in somites. The expression domains of ligands are complementary to those of the corresponding receptors in a number of tissues, including the midbrain, hindbrain, and differentiating limbs, consistent with potential roles in restricting cell movement. In addition, we find that there are some overlaps in expression of receptors and ligands, for example in somites and the early limb. Taken together with previous studies showing that Eph-related receptors also have distinct but overlapping expression patterns, these data indicate that each ligand may have stage- and tissue-specific interactions with an individual member or multiple members of the receptor family
Human E2F-1 Reactivates Cell Cycle Progression in Ventricular Myocytes and Represses Cardiac Gene Transcription

AbstractThe “pocket” protein- and p300-binding domains of E1A mediate alternative pathways that, independently, provoke S phase reentry in ventricular muscle cells and repress cardiac-specific transcription. In the present study, we utilized recombinant adenovirus to deliver mammalian E2F-1, whose release from pocket proteins may underlie effects of E1A and mitogenic signaling. Like E1A, E2F-1 proved cytotoxic in the absence of E1B. Used along with E1B to avert apoptosis, E2F-1 inhibited the cardiac and skeletal α-actin promoters, serum response factor abundance, and sarcomeric actin biosynthesis, while inducing DNA synthesis and proliferating cell nuclear antigen. Image analysis of Feulgen-stained nuclei corroborated a parallel increase in DNA content, with accumulation in G2/M. Thus, E2F-1 suffices for all observed actions of E1A in cardiac myocytes
An Identified Set of Visceral Muscle Bands Is Essential for the Guidance of Migratory Neurons in the Enteric Nervous System ofManduca sexta

AbstractDuring the formation of the enteric nervous system (ENS) inManduca,a population of ∼300 enteric neurons (the EP cells) become distributed along the foregut and midgut by migrating onto specific sets of visceral muscle bands. Only after their migration is complete do the neurons express a variety of position-specific phenotypes, including a peptidergic phenotype that is usually restricted to a subset of EP cells on the midgut. To investigate whether direct interactions between the EP cells and these pathways are necessary for either neuronal migration or differentiation, we have investigated the developmental origins and functional role of the muscle bands in embryonic culture. Using scanning electron microscopy, immunohistochemistry, and mitotic labeling with bromodeoxyuridine, we found that the eight major muscle bands of the midgut form by the coalescence of longitudinal muscle fibers on the midgut surface, apparently in response to regional cues associated with the underlying epithelium. These bands then serve as migratory pathways for the EP cells, which travel rapidly along the bands (but not onto adjacent interband musculature) and then complete their differentiation. Dye labeling of individual EP cells revealed that prior to migration onset, each neuron extended widely distributed filopodia onto both the band and interband regions of the midgut surface. As the muscle bands coalesced, however, the leading process of each EP cell became increasingly confined to a specific band, onto which it subsequently migrated. In a series of surgical manipulations of both the muscle bands and the migratory neurons, we demonstrated that these pathways are both necessary and sufficient to support the migratory behavior of the EP cells. Surgical interventions that prevented the neurons from contacting the muscle bands inhibited migration, while contact between isolated EP cells and a muscle band supported both their migration and differentiation. However, the acquisition of mature phenotypes by the EP cells was not strictly dependent on the migration of these neurons to their expected positions. In particular, the onset of neuropeptide expression could be detected in at least some of the neurons whose migration onto the midgut had been blocked. Thus, in the embryonic ENS, the migration and delayed differentiation of the EP cells represent precisely coordinated aspects of development that are nevertheless regulated in an independent manner
A Mutation in Zebrafish Affecting a Localized Cellular Function Required for Normal Ear Development

AbstractZebrafish holds great potential as a model system for studying inner ear development because genetic techniques are highly efficient and inner ear development is a conspicuous and manipulable feature of zebrafish embryogenesis. Here we describe analysis of a semilethal dominant mutation, termedmonolith(mnl), that specifically perturbs formation of the anterior (utricular) otolith in the developing ear. Other than the utricular otolith deficiency, all structures in the ear appear morphologically normal in mutant embryos, including posterior otoliths and all sensory epithelia. Expression patterns of several ear marker genes (msxC, msxD,anddlx3) also appear normal in the mutant. To identify the cell type(s) affected by themnlmutation, chimeras were generated by transplanting dye-labeled +/+ cells into unlabeledmnl/mnlhost embryos. Roughly half of such chimeras formed utricular otoliths normally, indicating that the transplanted wild-type cells rescued their mutant hosts. Detailed analysis of +/+ cell fates revealed that virtually all chimeras in which +/+ cells formed support cells in the utricular sensory epithelium were rescued. In contrast, wild-type cells forming other cell types (such as hair cells) or colonizing other regions of the host were not sufficient to facilitate rescue. These data indicate that support cells are required for normal otolith formation, providing the first experimentally established role for support cells in vertebrate sensory epithelia. The data also provide the first clear indication that otolith formation is controlled independently in different regions of the ear by localized cellular functions
The Initial Phase of Gastrulation in Sea Urchins Is Accompanied by the Formation of Bottle Cells

AbstractThe morphogenetic processes responsible for the initial phase of gastrulation in sea urchins have yet to be satisfactorily defined. Using conventional and confocal microscopy we have analyzed the buckling of the vegetal plate to form the archenteron in embryos ofStrongylocentrotus purpuratus.The cells of the vegetal plate elongate and a ring of 34 to 36 bottle cells forms within the vegetal plate during invagination. Rhodamine phalloidin staining reveals a reorganization of the actin cytoskeleton associated with these changes in cell shape. During buckling, the ring of bottle cells within the vegetal plate fluoresce intensely at their apical surface and in the narrow neck region. Ionophore A23187 induces precocious buckling and the formation of the ring of bottle cells. The calcium channel blocker verapamil and the calmodulin inhibitor trifluoperazine reversibly inhibit buckling and the formation of the ring of bottle cells. Treatment with antibodies to the apical lamina, which interferes with the initial stage of gastrulation, blocks the appearance of the vegetal plate phalloidin staining. Measurements of the dimensions of cells and an analysis of shape changes suggest that the formation of bottle cells reduces the surface area of the vegetal plate by more than 50%. We propose that actin-mediated changes in cell shape within the vegetal plate are responsible for producing forces which cause buckling of the vegetal plate during the initial phase of gastrulation
A Molecular Mechanism for Synapse Elimination: Novel Inhibition of Locally Generated Thrombin Delays Synapse Loss in Neonatal Mouse Muscle

AbstractActivity-dependent, polyneuronal synapse elimination (ADPSE) is a programmed, regressive event in the development of the nervous system and readily studied at the neuromuscular junction, where it is complete 15–20 days after birth. Local excess, or imbalanced, protease activity is one of several possible underlying mechanisms. In this regard, thrombin mediates activity-dependent synapse loss in anin vitromodel of ADPSE. To test the involvement of thrombinin vivo,we locally applied the leech thrombin-specific inhibitor, hirudin. We monitored neuromuscular behavior, correlated with acetylcholinesterase and silver nitrate histochemistry at endplates, for changes in the timecourse ofin vivosynapse elimination and assayed both thrombin activity and prothrombin expression in developing muscle. Hirudin retarded elimination, without altering motor performance, uniquely at Postnatal Day 5 (P5) and maximally at P9. Reverse transcription–polymerase chain reaction (PCR) showed that neonatal muscle was a source of local prothrombin, with peak expression during the first week after birth. A specific chromogenic assay revealed that local thrombin, activated from muscle-derived prothrombin, peaked during maximal synapse remodeling
Specific Induction of Apoptosis in P19 Embryonal Carcinoma Cells by Retinoic Acid and BMP2 or BMP4

AbstractRetinoic acid (RA) affects the response of many cells to growth factors, including the bone morphogenetic proteins (BMPs). The BMPs are members of the TGF-β family of growth factors, originally identified by their bone-inducing activities. Their widespread expression suggests many roles other than that in osteogenesis. Because RA modulates the cell's response to growth factors, this may be a means by which the retinoids exert some of their known teratogenic effects. One such cellular response may be apoptosis. While apoptosis is required for normal development, the location and timing of its induction must be carefully controlled. Recently, several TGF-β family members have been implicated in the induction of apoptosis in certain cell types. We show here, using P19 embryonal carcinoma cells, that the combination of RA and BMP2 or BMP4 synergistically induces apoptosis in 40% of the population within 24 hr. In contrast, RA alone induces apoptosis in only 10–15% of the population and each of the BMPs alone minimally induces apoptosis. Apoptosis depends on the dose of both the RA and the BMP as well as on new protein synthesis. Further, the induction of apoptosis prevents the formation of fully differentiated neurons and glial cells and instead leads to primarily smooth muscle cell differentiation. These results suggest that some of the malformations caused by retinoids may be due to the induction of inappropriate apoptosis in cells exposed to BMPs
Positive Feedback between MAP Kinase and Mos duringXenopusOocyte Maturation

AbstractMos is a serine–threonine protein kinase and a key regulator of meiosis. One function ofXenopusMos is to activate mitogen-activated protein kinase (MAPK) through direct phosphorylation and activation of MAPK kinase (MAPKK). All three members of this signal cascade can individually induce hormone-independent reentry of oocytes into meiosis I. However, their inducing efficiency is reduced in the absence of protein synthesis. Here we show thatde novoMos synthesis is required for induction of meiosis I by active MAPKK or Mos–MAPK coinjection. In addition, MAPK efficiently phosphorylates Mos at Ser-3in vitro.These results suggest that a positive feedback loop exists between MAPK and Mos during oocyte maturation.De novosynthesis of Mos, and other proteins, is required for progression from meiosis I to the metaphase arrest at meiosis II; therefore, one function of MAPK during normalXenopusoocyte maturation might be to stimulate the synthesis or accumulation of Mos that is required for the completion of meiosis
Evidence for the Existence of at Least Two Timing Mechanisms That Contribute to Oligodendrocyte Generationin Vitro

AbstractWe have been studying oligodendrocyte generationin vitroto obtain insights into how the timely generation of these cells might be regulated. Our studies suggest the existence of timing mechanisms quite different from those of existing models, wherein it is proposed that timely oligodendrocyte generation is associated with synchronous and symmetric differentiation controlled by cell-intrinsic biological clocks. Our results are most consistent with the hypothesis that the propensity of a clone of dividing oligodendrocyte type-2 astrocyte (O-2A) progenitors initially to generate at least one oligodendrocyte may be regulated by cell-intrinsic mechanisms, but that cell-extrinsic signals regulate the extent of further oligodendrocyte generation. In cultures of embryonic rat cortex grown in the presence of platelet-derived growth factor (PDGF), oligodendrocytes appeared in a timely manner in the absence of clonal differentiation. In contrast with previous suggestions, the presence or absence of thyroid hormone (T3) did not alter the probability of individual clones of O-2A progenitors generating at least one oligodendrocytein vitroat a time equal to the rat's day of birth. Instead, T3 increased the proportion of oligodendrocytes generated within clones. For postnatally derived progenitor cells, the initial appearance of oligodendrocytes also was followed by further asymmetric generation of these cells, with the ratio of progenitors to oligodendrocytes within clones being regulated by environmental signals. T3 and ciliary neurotrophic factor increased oligodendrocyte generation, while neurotrophin-3 (NT-3) suppressed oligodendrocyte generation. Also in contrast to previous reports, NT-3 was not required for the promotion of extensive division of O-2A progenitor cells by PDGF
Synergistic Effects of Vg1 and Wnt Signals in the Specification of Dorsal Mesoderm and Endoderm

AbstractIn amphibians, dorsoventral asymmetry is established by cortical rotation, a cytoplasmic rearrangement in the egg which activates a dorsal determinant on one side of the zygote. This determinant has been proposed to be either Vg1, an endodermally derived molecule that can directly induce ectoderm to form dorsal mesoderm, or a member of the Wnt family, which patterns the ectoderm such that it forms dorsal mesoderm in response to ventral inductive signals. In this study, we have investigated whether the endogenous dorsal determinant(s) functions as a direct inducer of dorsal mesoderm (Vg1-like) or whether it acts to pattern the response of ectoderm to inductive signals (Wnt-like). We report here that cortical rotation enhances both the dorsal-inductive activity of endodermal cells and the response of ectodermal cells to endogenous inductive signals and that both of these activities are required for notochord induction in ectoderm/endoderm recombinants. While ectopically expressed Xwnt-8b can substitute for the dorsalizing signals activated in either ectoderm or endoderm, and can allow notochord formation in recombinants, Vg1 alone is not sufficient to induce notochord in ectodermal explants in the absence of signals activated by cortical rotation. Coexpression of Xwnt-8b along with Vg1 restores ectodermal competence to form notochord. Finally, in endodermal explants, ectopically expressed Xwnt-8b, but not Vg1, can divert the fate of ventral endodermal cells along a dorsal pathway. Thus, while Vg1 is most likely required for induction of mesodermin vivo,our data suggest that a maternal Wnt-like signal acts synergistically with Vg1 to specify a dorsal fate not only in the mesoderm, but also in the endoderm
Surgical Removal of Limb BudSonic hedgehogResults in Posterior Skeletal Defects

AbstractUsingSonic Hedgehog(Shh) as a marker for polarizing region cells we have repeated the experiments of MacCabeet al.(1973) and Fallon and Crosby (1975) in an attempt to reexamine the question of a continuous role for the polarizing region during limb development. We report that the earlier experiments probably leftShh-expressing cells after surgery. Our results show thatShh-expressing cells do not regenerate and complete removal of the polarizing region results in truncations along the anteroposterior (A–P) axis; further, A–P patterning cannot be restored when a bead soaked in FGF is implanted in the limb bud mesenchyme to maintain outgrowth after extirpation of the polarizing region. However, in order to reproducibly remove allShh-positive cells, it is possible that cells with posterior limb skeletal fate also must be removed. Therefore, microsurgical approaches do not permit an unequivocal answer to the question raised in this and the earlier papers and it remains a reasonable possibility that at least up to stage 20–21 the polarizing region plays a continuous role in patterning of the limb bud during its development
Expression Pattern of Collagen IX and Potential Role in the Segmentation of the Peripheral Nervous System

AbstractSegmentation of the peripheral nervous system of vertebrates requires guidance cues located in the adjacent somitic mesoderm. Recent experiments suggest that inhibitory molecules in the posterior somite may influence segmentation by restricting the outgrowth of axons and the migration of neural crest cells to the anterior somite. A potential candidate for an inhibitory molecule is collagen IX, a chondroitin sulfate proteoglycan made by sclerotome cells of the somite and by the notochord. Immunohistochemical localization of collagen IX demonstrated that its expression in the posterior sclerotome of the somite correlates with axon outgrowth and neural crest cell migration through the anterior sclerotome.In vitro,sensory neurites on fibronectin, and motor neurites on basal lamina extract, avoid regions which contain substrate-bound collagen IX. This effect can be abolished by chondroitinase treatment, suggesting that the glycosaminoglycan component of the molecule is responsible for this activity. Further, collagen IX elicits a similar avoidance behavior by neural crest cellsin vitro.These data suggest that collagen IX contributes to the segmentation of the peripheral nervous systemin vivo
Ooplasmic Redistribution inTubifexEggs with Selectively Impaired Cortical Actin Cytoskeleton

AbstractTubifexeggs contain two configurations of actin cytoskeleton (AC): a cortical thin shell of densely packed actin filaments and an endoplasmic loose network of actin filaments. Here we show that microinjection of botulinum C3 exoenzyme (ADP-ribosyltransferase) intoTubifexeggs disrupts the cortical AC, but not the endoplasmic AC. C3 exclusively ADP-ribosylates a 24-kDa protein in theTubifexegg, suggesting the involvement of this protein in the regulation of the cortical AC. Among the actin-dependent processes that occur during maturation divisions and the first cell cycle, only outward migration of ooplasm (viz., early stage of the first step of ooplasmic segregation) occurs in C3-injected eggs, although migrating ooplasm is organized into patches rather than a continuous layer as observed in intact eggs. This ooplasmic movement is inhibited by cytochalasin D treatments. These results suggest that the endoplasmic AC is able to move ooplasm centrifugally in the absence of the cortical AC. In contrast, poleward movement of subcortical ooplasm along the egg surface (viz., the second step of ooplasmic segregation) is completely abolished in C3-injected eggs, even though the endoplasmic AC is present in the subcortical ooplasm
The Nonreceptor Protein Tyrosine Phosphatase Corkscrew Functions in Multiple Receptor Tyrosine Kinase Pathways inDrosophila

AbstractCorkscrew(csw) encodes a nonreceptor protein tyrosine phosphatase (PTPase) that has been implicated in signaling from the Torso receptor tyrosine kinase (RTK).cswmutations, unliketormutations, are associated with zygotic lethality, indicating that Csw plays additional roles during development. We have conducted a detailed phenotypic analysis ofcswmutations to identify these additional functions of Csw. Our results indicate that Csw operates positively downstream of otherDrosophilaRTKs such as theDrosophilaepidermal growth factor receptor (DER), the fibroblast growth factor receptor (Breathless), and likely other RTKs. This model is substantiated by specific dosage interactions betweencswandDER.It is proposed that Csw is part of the evolutionarily conserved “signaling cassette” that operates downstream of all RTKs. In support of this hypothesis, we demonstrate that SHP-2, a vertebrate PTPase similar to Csw and previously implicated in RTK signaling, encodes the functional vertebrate homologue of Csw
Widespread Expression of β1 Integrins in the Developing Chick Retina: Evidence for a Role in Migration of Retinal Ganglion Cells

AbstractDuring extension of axons, critical neuronal interactions with extracellular matrix (ECM) and other cells are thought to be mediated in part by heterodimeric β1 integrin receptors. In this report, we examine the expression and function of β1 integrins in the developing chick retina. Expression of the β1 subunit, assayed byin situhybridization and antibody staining of dissociated cells, was widespread in undifferentiated neuroepithelial cells, before the initiation of axons. Expression persisted in most retinal cell layers throughout embryonic development, during and after axon extension. The repertoire of β1-associated α subunits was examined using reverse transcription–polymerase chain reaction. In addition to the α6 and α8 subunits previously reported, chick homologues of the α2 and α4 subunits were detected. Developmental Northern blots revealed varying patterns of integrin subunit expression and showed that expression of β1 and the mRNAs of its associated α subunits are not always coregulated during retinal development. The timing and distribution of expression suggested that β1 integrins may be involved in other developmental events in addition to axon extension. To address functions carried out by β1 integrins in the early retina, explanted eye cups were incubated in the presence of function blocking anti-β1 antibody and migration of newly born retinal ganglion cells (RGCs) was assessed. RGC migration from the ventricular zone to the vitreal border was significantly inhibited, suggesting that β1 integrins play a role in neuroblast migration in the retina