pinecone/core-2020-05-10-deduplication huggingface dataset:
Cell Type-Specific Expression of Fasciclin II Isoforms Reveals Neuronal–Glial Interactions during Peripheral Nerve Growth

AbstractDuring the formation of the insect peripheral nervous system (PNS), the cell adhesion receptor fasciclin II has been shown to play a prominent role in axonal fasciculation and synapse formation during motor neuron outgrowth. In the moth Manduca, fasciclin II (MFas II) is expressed both as a transmembrane isoform (TM-MFas II) and a glycosyl phosphatidylinositol-linked isoform (GPI-MFas II). By using RNA and antibody probes, we have shown that these two isoforms are expressed in nonoverlapping patterns: TM-MFas II is expressed exclusively by neurons and becomes localized to their most motile regions, while GPI-MFas II is expressed primarily by the glial cells that ensheath the peripheral nerves. This cell-type specificity of expression allowed us to monitor the nature of neuronal–glial interactions during PNS development. The outgrowth of TM-MFas II-positive axons in many regions preceded the arrival of GPI-MFas II-expressing glial processes that enwrapped them. In a few key locations, however, GPI-MFas II-positive glial cells differentiated before the arrival of the first axons and prefigured their subsequent trajectories. Prior inhibition of GPI-MFas II expression disrupted the subsequent outgrowth of axons at these locations but not elsewhere in the PNS. Our results suggest that the two isoforms of MFas II play distinct roles with respect to cellular motility and nerve formation
Differential Adhesion Leads to Segregation and Exclusion of N-Cadherin-Deficient Cells in Chimeric Embryos

AbstractCadherin-mediated cell–cell interactions are thought to be critical in controlling cell sorting during embryogenesis. Here, we report that chimeric embryos generated with N-cadherin-deficient (N-cadherin−/−) embryonic stem cells develop further than embryos completely lacking N-cadherin only when the myocardium consists of N-cadherin-positive cells. Initially, the N-cadherin-negative and -positive cells mix together to form chimeric tissues; however, by embryonic day 9.5, the N-cadherin−/− cells segregate from the wild-type cells forming distinct aggregates. The chimeric embryos have large aggregates of N-cadherin−/− myocardial cells in the heart lumen, indicating that the cells are unable to maintain cell–cell contacts with N-cadherin-positive myocytes. This sorting-out phenomenon also is apparent in somites, neural tube, and developing brain where N-cadherin−/− cells form distinct lumenal structures. These studies demonstrate that N-cadherin-mediated adhesion is critical for maintaining cell–cell interactions in tissues undergoing active cellular rearrangements and increased mechanical stress associated with morphogenesis
Mutation of the Zebrafish glass onion Locus Causes Early Cell-Nonautonomous Loss of Neuroepithelial Integrity Followed by Severe Neuronal Patterning Defects in the Retina

AbstractMutation of the glass onion locus causes drastic neuronal patterning defects in the zebrafish retina and brain. The precise stratified appearance of the wild-type retina is absent in the mutants. The glass onion phenotype is first visible shortly after the formation of optic primordia and is characterized by the rounding of cells and disruption of the ventricular surface in the eye and brain neuroepithelia. With exception of the dorsal- and ventral-most regions of the brain, neuroepithelial cells lose their integrity and begin to distribute ectopically. At later stages, the laminar patterning of retinal neurons is severely disrupted. Despite the lack of lamination, individual retinal cell classes differentiate in the glass onion retina. Mosaic analysis reveals that the glass onion mutation acts cell nonautonomously within the retina and brain, as neuroepithelial cell morphology and polarity in these tissues are normal when mutant cells develop in wild-type hosts. We conclude that the glass onion mutation affects cell–cell signaling event(s) involved in the maintenance of the neuroepithelial cell layer shortly after its formation. The disruption of neuroepithelial integrity may be the cause of the neuronal patterning defects following neurogenesis. In addition, the expression of the glass onion phenotype in a subset of neuroepithelial cells as well as its onset following the initial formation of the neuroepithelial sheets indicate the presence of genetically distinct temporal and spatial subdivisions in the development of this histologically uniform tissue
Simultaneous Measurement of Intracellular Nitric Oxide and Free Calcium Levels in Chordate Eggs Demonstrates That Nitric Oxide Has No Role at Fertilization

AbstractAt fertilization in sea urchin, the free radical nitric oxide (NO) has recently been suggested to cause the intracellular Ca2+ rise responsible for egg activation. The authors suggested that NO could be a universal activator of eggs and the present study was set up to test this hypothesis. Intracellular NO and Ca2+ levels were monitored simultaneously in eggs of the mouse or the urochordate ascidian Ascidiella aspersa. Eggs were either fertilized or sperm extracts microinjected. Sperm-induced Ca2+ rises were not associated with any global, or local, change in intracellular NO, although we were able to detect NO produced by the addition of a NO donor. Furthermore, the NO synthase inhibitor NG-nitro-l-arginine methyl ester had no effect on sperm-induced Ca2+ release but did block completely ionomycin-induced NO synthase activation. Therefore, we suggest that the current data provide evidence that NO has no role in the fertilization of these two chordate eggs
Axis Induction by Wnt Signaling: Target Promoter Responsiveness Regulates Competence

AbstractThe modulation of inductive competence is a major theme in embryonic development, but, in most cases, the underlying mechanisms are not well understood. In principle, the capacity of extracellular signals to elicit particular responses could be regulated by changes in cell surface receptors, in intracellular signaling pathways, or in the responsiveness of individual target gene promoters. As an example of regulated competence, we have examined dorsal axis induction in Xenopus embryos by Wnt signaling. Competence of Wnt proteins such as Xwnt-8 to induce an ectopic axis or the dorsal early response genes siamois and Xnr3 is lost by the onset of gastrulation, when these same ligands now produce a distinct set of “late” effects, including anterior truncation and induction of the midbrain/hindbrain marker engrailed-2. Although other Wnts apparently make use of alternative signaling mechanisms, we demonstrate that late-expressed Xwnt-8 continues to employ the canonical Wnt signaling pathway used earlier in dorsal axis induction, stabilizing cytosolic β-catenin, and activating gene expression through Tcf/Lef transcription factors. Moreover, an activated, hormone-inducible version of XTcf-3 (TVGR) that can reproduce both early and late Wnt responses when activated at appropriate stages becomes unable to induce siamois and secondary axes at the same time as Wnt ligands themselves. Finally, we show that TVGR also loses the ability to induce expression of a reporter construct containing a small fragment of the siamois promoter, implying that this fragment contains sequences governing the loss of Wnt responsiveness before gastrulation. Together, these results argue that the competence of Wnts to induce a dorsal axis is lost in the nucleus, as a result of changes in the responsiveness of target promoters
Positive and Negative Regulation of Epicardial–Mesenchymal Transformation during Avian Heart Development

AbstractIn the developing heart, the epicardium is essential for coronary vasculogenesis as it provides precursor cells that become coronary vascular smooth muscle and perivascular fibroblasts. These precursor cells are derived from the epicardium via epithelial–mesenchymal transformation (EMT). The factors that regulate epicardial EMT are unknown. Using a quantitative in vitro collagen gel assay, we show that serum, FGF-1, -2, and -7, VEGF, and EGF stimulate epicardial EMT. TGFβ-1 stimulates EMT only weakly, while TGFβ-2 and -3 do not stimulate EMT. TGFβ-1, -2, or -3 strongly inhibits transformation of epicardial cells stimulated with FGF-2 or heart-conditioned medium. TGFβ-3 does not block expression of vimentin, a mesenchymal marker, but appears to inhibit EMT by blocking epithelial cell dissociation and subsequent extracellular matrix invasion. Blocking antisera directed against FGF-1, -2, or -7 substantially inhibit conditioned medium-stimulated EMT in vitro, while antibodies to TGFβ-1, -2, or -3 increase it. We confirmed FGF stimulation and TGFβ inhibition of epicardial EMT in organ culture. Immunoblot analysis confirmed the presence of FGF-1, -2, and -7 and TGFβ-1, -2, and -3 in conditioned medium, and we localized these growth factors to the myocardium and epicardium of stage-appropriate embryos by immunofluorescence. Our results strongly support a model in which myocardially derived FGF-1, -2, or -7 promotes epicardial EMT, while TGFβ-1, -2, or -3 restrains it. Epicardial EMT appears to be regulated through a different signaling pathway than endocardial EMT
Tantalus, a Novel ASX-Interacting Protein with Tissue-Specific Functions

AbstractThe Drosophila trithorax- and Polycomb-group (trxG and PcG) proteins maintain activated and repressed transcriptional states at specific target gene loci. The Additional sex combs (Asx) gene is of particular interest as it appears to function in both protein complexes and yet its effects on target genes are more restricted. A novel protein, Tantalus (TAN), was identified in a yeast two-hybrid screen for ASX-interacting proteins that might confer tissue-specific ASX functions. TAN contains consensus nuclear localization sites and binds DNA in vitro. However, its subcellular localization varies in a tissue-specific fashion. In salivary glands, TAN is predominantly nuclear and associates with 66 euchromatic sites on polytene chromosomes, more than half of which overlap with ASX. These loci do not include the homeotic genes of the ANT and BX complexes bound by other PcG and trxG proteins. Rather, tan mutant defects are restricted to sensory organs. We show that one of these defects, shared by Asx, is genetically enhanced by Asx. Taken together, the data suggest that TAN is a tissue-specific cofactor for ASX, and that its activity may be partially controlled by subcellular trafficking
Chick CFC Controls Lefty1 Expression in the Embryonic Midline and Nodal Expression in the Lateral Plate

AbstractMembers of the EGF-CFC family of proteins have recently been implicated as essential cofactors for Nodal signaling. Here we report the isolation of chick CFC and describe its expression pattern, which appears to be similar to Cfc1 in mouse. During early gastrulation, chick CFC was asymmetrically expressed on the left side of Hensen's node as well as in the emerging notochord, prechordal plate, and lateral plate mesoderm. Subsequently, its expression became confined to the heart fields, notochord, and posterior mesoderm. Implantation experiments suggest that chick CFC expression in the lateral plate mesoderm is dependent on BMP signaling, while in the midline its expression depends on an Activin-like signal. The asymmetric expression domain within Hensen's node was not affected by application of FGF8, Noggin, or Shh antibody. Implantation of cells expressing human or mouse CFC2, or chick CFC on the right side of Hensen's node randomized heart looping without affecting expression of genes involved in left–right axis formation, including SnR, Nodal, Car, or Pitx2. Application of antisense oligodeoxynucleotides to the midline of Hamburger–Hamilton stage 4-5 embryos also randomized heart looping, but in contrast to the overexpression experiments, antisense oligodeoxynucleotide treatment resulted in bilateral expression of Nodal, Car, Pitx2, and NKX3.2, whereas Lefty1 expression in the midline was transiently lost. Application of the antisense oligodeoxynucleotides to the lateral plate mesoderm abolished Nodal expression. Thus, chick CFC seems to have a dual function in left–right axis formation by maintaining Nodal expression in the lateral plate mesoderm and controlling expression of Lefty1 expression in the midline territory
Neural Induction in the Absence of Mesoderm: β-Catenin-Dependent Expression of Secreted BMP Antagonists at the Blastula Stage in Xenopus

AbstractA growing body of work indicates that neural induction may be initiated prior to the establishment of the gastrula mesodermal organizer. Here, we examine neural induction in Xenopus embryos in which mesoderm induction has been blocked by Cerberus-short, a reagent that specifically inhibits Nodal-related (Xnr) signals. We find that extensive neural structures with cyclopic eyes and brain tissue are formed despite the absence of mesoderm. This neural induction correlates with the expression of chordin and other BMP inhibitors—such as noggin, follistatin, and Xnr3—at the blastula stage, and requires β-Catenin signaling. Activation of the β-Catenin pathway by mRNA microinjections or by treatment with LiCl leads to differentiation of neurons, as well as neural crest, in ectodermal explants. Xnr signals are required for the maintenance, but not for the initiation, of BMP antagonist expression. Recent work has demonstrated a role for β-Catenin signaling in neural induction mediated by the transcriptional down-regulation of BMP-4 expression. The present results suggest an additional function for β-Catenin, the early activation of expression of secreted BMP antagonists, such as Chordin, in a preorganizer region in the dorsal side of the Xenopus blastula
Bmp2b and Oep Promote Early Myocardial Differentiation through Their Regulation of gata5

AbstractMembers of both the bone morphogenetic protein (Bmp) and EGF-CFC families have been implicated in vertebrate myocardial development. Zebrafish swirl (swr) encodes Bmp2b, a member of the Bmp family required for patterning the dorsoventral axis. Zebrafish one-eyed pinhead (oep) encodes a maternally and zygotically expressed member of the EGF-CFC family essential for Nodal signaling. Both swr/bmp2b and oep mutants exhibit severe defects in myocardial development. swr/bmp2b mutants exhibit reduced or absent expression of nkx2.5, an early marker of the myocardial precursors. Embryos lacking zygotic oep (Zoep mutants) display cardia bifida and, as we show here, also display reduced or absent nkx2.5 expression. Recently, we have demonstrated that the zinc finger transcription factor Gata5 is an essential regulator of nkx2.5 expression. In this paper, we investigate the relationships between bmp2b, oep, gata5, and nkx2.5. We show that both swr/bmp2b and Zoep mutants exhibit defects in gata5 expression in the myocardial precursors. Forced expression of gata5 in swr/bmp2b and Zoep mutants restores robust nkx2.5 expression. Moreover, overexpression of gata5 in Zoep mutants restores expression of cmlc1, a myocardial sarcomeric gene. These results indicate that both Bmp2b and Oep regulate gata5 expression in the myocardial precursors, and that Gata5 does not require Bmp2b or Oep to promote early myocardial differentiation. We conclude that Bmp2b and Oep function at least partly through Gata5 to regulate nkx2.5 expression and promote myocardial differentiation. We integrate these and other data to propose a pathway of the molecular events regulating early myocardial differentiation in zebrafish
Cyclin E and Its Associated cdk Activity Do Not Cycle during Early Embryogenesis of the Sea Urchin

AbstractFemale sea urchins store their gametes as haploid eggs. The zygote enters S-phase 1 h after fertilization, initiating a series of cell cycles that lack gap phases. We have cloned cyclin E from the sea urchin Strongylocentrotus purpuratus. Cyclin E is synthesized during oogenesis, is present in the germinal vesicle, and is released into the egg cytoplasm at oocyte maturation. Cyclin E synthesis is activated at fertilization, although there is no increase in cyclin E protein levels due to continuous turnover of the protein. Cyclin E protein levels decline in morula embryos, while cyclin E mRNA levels remain high. After the blastula stage, cyclin E mRNA and protein levels are very low, and cyclin E expression is predominant only in cells that are actively dividing. These include cells in the left coelomic pouch, which forms the adult rudiment in the embryo. The cyclin E present in the egg is complexed with a protein kinase. Activity of the cyclin E/cdk2 changes little during the initial cell cycles. In particular, cyclin E-cdk2 levels remain high during both S-phase and mitosis. Our results suggest that progression through the early embryonic cell cycles in the sea urchin does not require fluctuations in cyclin E kinase activity
Overexpression of Camello, a Member of a Novel Protein Family, Reduces Blastomere Adhesion and Inhibits Gastrulation in Xenopus laevis

AbstractVertebrate gastrulation involves complex coordinated movements of cells and cell layers to establish the axial structures and the general body plan. Adhesion molecules and the components of extracellular matrix were shown to be involved in this process. However, other participating molecules and detailed mechanisms of the control of gastrulation movements remain largely unknown. Here, we describe a novel Xenopus gene camello (Xcml) which is expressed in the suprablastoporal zone of gastrulating embryos. Injection of Xcml RNA into dorsovegetal blastomeres retards or inhibits gastrulation movements. Database searches revealed a family of mammalian mRNAs encoding polypeptides highly similar to Xcml protein. Characteristic features of the camello family include the presence of the central hydrophobic domain and the N-acetyltransferase consensus motifs in the C-terminal part, as well as functional similarity to Xcml revealed by overexpression studies in Xenopus embryos. Xcml expression results in the decrease of cell adhesion as demonstrated by the microscopic analysis and the blastomere aggregation assay. Cell fractionation and confocal microscopy data suggest that Xcml protein is localized in the secretory pathway. We propose that Xcml may fine tune the gastrulation movements by modifying the cell surface and possibly extracellular matrix proteins passing through the secretory pathway
Dosage-Dependent Gene Regulation in Multicellular Eukaryotes: Implications for Dosage Compensation, Aneuploid Syndromes, and Quantitative Traits

AbstractEvidence from a variety of data suggests that regulatory mechanisms in multicellular eukaryotes have evolved in such a manner that the stoichiometric relationship of the components of regulatory complexes affects target gene expression. This type of mechanism sets the level of gene expression and, as a consequence, the phenotypic characteristics. Because many types of regulatory processes exhibit dosage-dependent behavior, they would impact quantitative traits and contribute to their multigenic control in a semidominant fashion. Many dosage-dependent effects would also account for the extensive modulation of gene expression throughout the genome that occurs when chromosomes are added to or subtracted from the karyotype (aneuploidy). Moreover, because the majority of dosage-dependent regulators act negatively, this property can account for the up-regulation of genes in monosomics and hemizygous sex chromosomes to achieve dosage compensation
Nuclear Plasticity and Timing Mechanisms of the Initiation of Alkaline Phosphatase Expression in Cytoplasm-Transferred Blastomeres of Ascidians

AbstractEgg cytoplasm containing endoderm determinants was transferred to presumptive-muscle or presumptive-epidermis blastomeres isolated from cleavage-stage embryos of the ascidian Halocynthia roretzi. We investigated three aspects of the expression of endoderm-specific alkaline phosphatase (ALP) activity. First, we examined whether ectopic ALP expression, an indication of ectopic endoderm formation, was promoted in cytoplasm-transferred blastomeres isolated at late-cleavage stage. The results showed that the cell fate was converted by the introduced cytoplasm, even in recipient blastomeres in which the cell fate was already restricted to muscle or epidermis, and in those where expression of the muscle- or epidermis-specific genes was already initiated. Next, we examined the formation of endoderm and other tissue in embryos by double staining for ALP and muscle- or epidermis-specific marker. Regions positive for ALP and positive for muscle or epidermis marker were mutually exclusive. These results suggested that muscle- or epidermis-specific genes that were already expressed in the recipient blastomeres were down-regulated in ectopically forming endoderm cells. This is evidence for nuclear plasticity during ascidian embryogenesis. In the last series of experiments, we investigated the timing of the appearance of ALP activity in cytoplasm-transferred embryos. In the partial embryos that were derived from various combination of recipient blastomeres and donor cytoplasm obtained from various staged eggs and embryos, the timing seemed to coincide with the time that starts when cell fusion for cytoplasmic transfer was done. Therefore, the clock that determines the timing of the initiation of ALP expression is likely to start at the moment of cell fusion. Several possible hypotheses for the timing mechanism are discussed
Expression of Axolotl DAZL RNA, a Marker of Germ Plasm: Widespread Maternal RNA and Onset of Expression in Germ Cells Approaching the Gonad

AbstractHow germ cell specification occurs remains a fundamental question in embryogenesis. The embryos of several model organisms contain germ cell determinants (germ plasm) that segregate to germ cell precursors. In other animals, including mice, germ cells form in response to regulative mechanisms during development. To investigate germ cell determination in urodeles, where germ plasm has never been conclusively identified, we cloned a DAZ-like sequence from axolotls, Axdazl. Axdazl is homologous to Xdazl, a component of Xenopus germ plasm found in the vegetal pole of oocytes and eggs. Axdazl RNA is not localized in axolotl oocytes, and, furthermore, these oocytes do not contain the mitochondrial cloud that localizes Xdazl and other germ plasm components in Xenopus. Maternal Axdazl RNA is inherited in the animal cap and equatorial region of early embryos. At gastrula, neurula, and tailbud stages, Axdazl RNA is widely distributed. Axdazl first shows cell-specific expression in primordial germ cells (PGCs) approaching the gonad at stage 40, when nuage (germ plasm) appears in PGCs. These results suggest that, in axolotls, germ plasm components are insufficient to specify germ cells