pinecone/core-2020-05-10-deduplication huggingface dataset:
Specification of the Hindbrain Fate in the Zebrafish

AbstractWe determine the timing of neural commitment by hindbrain tissue in the zebrafish using microsurgical transplantation. When transplanted at shield stage to the ventral side of the embryo, presumptive hindbrain cells are not committed, as they can adapt to their environment and give rise to epidermis. In contrast, when transplanted at 80% epiboly, hindbrain cells retain their neural fate and express neural-specific antigens. Moreover, they are able to maintain regional fate, as is evident by the expression of the hindbrain-specific marker, Krox20. In addition, we observe that committed hindbrain tissues are able to induce presumptive ventral epidermis to form neural crest derivatives, otic vesicles, and neural tissues. We propose that hindbrain progenitors have acquired regional identity as a group at 80% epiboly even before making vertical contact with axial mesoderm. These results suggest that planar induction may constitute a significant component in the zebrafish neural patterning pathway
Fiber Apoptosis in Developing Rat Muscles Is Regulated by Activity, Neuregulin

AbstractMotor neurons are thought to critically regulate the survival of a subset of developing muscle fibers. In muscles that develop in the absence of innervation, primary muscle fibers appear to form in normal numbers, but their long-term survival is thought to require innervation-induced suprathreshold activity. Here I examine interactions between motor neurons and muscle fibers in newborn rats. I report that a small fraction of muscle fibers in developing muscles undergo apoptosis. Many, if not all, of these fibers appear to have lost innervation owing to the retraction of nerve terminals. That the apoptosis is initiated by the loss of functional innervation is suggested by a severalfold increase in the magnitude of fiber apoptosis following denervation and muscle paralysis. Finally, both naturally occurring and denervation-induced muscle fiber apoptosis can be prevented by exogenous administration of neuregulin. These results argue that the survival of all or a subset of developing muscle fibers is ultimately regulated by neuregulin. Furthermore, these results suggest a model in which innervation-induced suprathreshold activity indirectly regulates muscle fiber survival by modulating the levels of neuregulin at developing neuromuscular junctions
Involvement of Thyroid Hormone and Its α Receptor in Avian Neurulation

AbstractWe have analyzed the expression pattern of c-erbAα and c-erbAβ which encode the thyroid hormone receptors (T3Rα and T3Rβ) during early chicken embryogenesis. Only c-erbAα expression was detected by RT-PCR and whole-mountin situhybridization. c-erbAα transcripts were found to be already present at low level in embryos before egg incubation. During neurulation a marked increase was observed in neurectoderm. A reporter cell line was then constructed and used to demonstrate the release of significant amount of thyroid hormone (T3) from egg yolk by area opaca cells before gastrulation. During gastrulation T3 was found to be enriched in the primitive streak and Hensen's node. Introduction of excess T3 frequently resulted in abnormal development of anterior structures, mainly neural tube defects and anencephalia. These observations suggest that T3Rα, like the closely related retinoic acid receptors, fulfills functions which are important for embryonic development well before the onset of thyroid gland function
Multiple Elements RegulateMash1Expression in the Developing CNS

AbstractMash1, a transcription factor of the basic helix–loop–helix class, is expressed during embryogenesis in restricted regions of the nervous system. An essential role for Mash1 in neural development was demonstrated previously in mice carrying a targeted disruption of theMash1gene. Regulation of the precise temporal and spatial expression ofMash1is thus likely to be important for proper neural development. In this study, sequences that regulateMash1expression in the central nervous system were characterized by assaying the expression oflacZreporter genes in transgenic embryos. A 1158-bp enhancer localized ∼7 kb upstream of theMash1coding region was identified. Deletions within this enhancer region reveal the presence of both positive and negativecis-acting elements. Analysis of multiple sequences within the enhancer demonstrate that different elements preferentially function in different regions within theMash1-specific CNS expression domain. In addition, a role for sequences 3′ of theMash1coding region is revealed, providing evidence for posttranscriptional control ofMash1expression in multiple CNS domains
Na/K-ATPase-Mediated86Rb+Uptake and Asymmetrical Trophectoderm Localization of α1 and α3 Na/K-ATPase Isoforms during Bovine Preattachment Development

AbstractThis study evaluated Na/K-ATPase α1- and α3-subunit isoform polypeptide expression and localization during bovine preattachment development. Na/K-ATPase cation transport activity from the one-cell to blastocyst stage was also determined by measuring ouabain-sensitive86Rb+uptake. Both α1- and α3-subunit polypeptides were detected by immunofluorescence to encircle the entire cell margins of each blastomere of inseminated zygotes, cleavage stage embryos, and morulae. Immunofluorescent localization of α1-subunit polypeptide in bovine blastocysts revealed an α1 immunofluorescence signal confined to the basolateral membrane margins of the trophectoderm and encircling the cell periphery of each inner cell mass (ICM) cell. In contrast, α3-subunit polypeptide immunofluorescence was localized primarily to the apical cell surfaces of the trophectoderm with a reduced signal present in basolateral trophectoderm regions. There was no apparent α3-subunit signal in the ICM. Analysis of86Rb+transportin vitrodemonstrated ouabain-sensitive activity throughout development from the one-cell to the six- to eight-cell stage of bovine development.86Rb+uptake by morulae (day 6 postinsemination) did not vary significantly from uptake detected in cleavage stage embryos; however, a significant increase was measured at the blastocyst stage (P< 0.05). Treatment of embryos with cytochalasin D (5 μg/ml) did not influence86Rb+uptake in cleavage stage embryos. Cytochalasin D treatment however was associated with a significant rise in ion transport in morulae and blastocysts (13.49 and 61.57 fmol/embryo/min, respectively) compared to untreated controls (2.65 and 22.83 fmol/embryo/min, respectively). Our results, for the first time, demonstrate that multiple Na/K-ATPase α-subunit isoforms are distributed throughout the first week of mammalian development and raise the possibility that multiple isozymes of the Na/K-ATPase contribute to blastocyst formation
The Role of Morphogenetic Cell Death duringDrosophilaEmbryonic Head Development

AbstractThis article addresses the role of programmed cell death (apoptosis) during embryonic head development ofDrosophila.Previous studies showed thatreaper(rpr) is expressed in and required by cells undergoing apoptosis. We have analyzed the correlation between the pattern of expression ofrprand morphogenetic movements affecting head development. Furthermore, we have investigated the defects in head development resulting from the absence of apoptosis in embryos deficient forrpr.Our results show that, in the head, domains of high incidence of cell death as marked by expression ofrprcorrelate with regions where most morphogenetic movements occur; these regions are involved in formation of mouth structures, the internalization of neural progenitors, and head involution. Cellular events driving these movements are delamination, invagination, and intercalation as well as disruption and reformation of contacts among epithelial cells. The analysis ofrpr-deficient embryos demonstrates that, despite of the widespread occurrence of apoptosis during normal head morphogenesis, many aspects of this process proceed in an apparently unperturbed manner even when cell death is blocked. In particular, movements that happen early during embryonic development and that are evolutionarily more ancient (e.g., formation of the dorsal ridge and the pharynx) take place almost normally inrpr-deficient embryos. Later events which are mostly associated with head involution (e.g., retraction of the clypeolabrum, formation of the dorsal pouch, fusion of lateral gnathal lobes) are evolutionarily more recent and fail to occur normally inrpr-deficient embryos
GDNF and ET-3 Differentially Modulate the Numbers of Avian Enteric Neural Crest Cells and Enteric Neuronsin Vitro

AbstractVagal (hindbrain) neural crest cells migrate rostrocaudally in the gut to establish the enteric nervous system. Glial-derived neurotrophic factor (GDNF) and its receptor(s), and endothelin-3 (ET-3) and its receptor, are crucial for enteric nervous system development. Mutations interrupting either of these signaling pathways cause aganglionosis in the gut, termed Hirschsprung's disease in humans. However, the precise functions of GDNF and ET-3 in enteric neurogenesis are still unknown. We isolated precursor cells of the enteric nervous system from the vagal level neural crest of E1.7 quail embryos prior to entry into the gut and from the developing midgut at stages corresponding to migrating (E4.7) and longer resident differentiating cells (E7) using HNK-1 immunoaffinity and magnetic beads. These cells were tested for their response to GDNF and ET-3 in culture. ET-3 and GDNF had little effectin vitroon the growth, survival, migration, or neurogenesis of E1.7 vagal neural crest cells. In contrast, GDNF increased the proliferation rate and numbers of enteric neural precursors isolated from the E4.7 and E7 gut. Also, many more neurons and neurites developed in cultures treated with GDNF, disproportionately greater than the effect on cell numbers. At high cell density and in the presence of serum, ET-3, and GDNF had an additive effect on proliferation of neuron precursor cells. In defined medium, or low cell density, ET-3 reduced cell proliferation, overriding the proliferative effect of GDNF. Regardless of the culture condition, the stimulatory effect of GDNF on neuron numbers was strikingly diminished by the simultaneous presence of ET-3. We propose first that GDNF promotes the proliferation in the migratory enteric neural precursor cell population once the cells have entered the gut and is especially crucial for the differentiation of these cells into nonmigrating, nonproliferating enteric neurons. Second, we suggest that ET-3 modulates the action of GDNF, inhibiting neuronal differentiation to maintain the precursor cell pool, so ensuring sufficient population numbers to construct the entire enteric nervous system. Third, we suggest that generalized defects in enteric neural precursor cell numbers and differentiation due to mutations in the ET-3 and GDNF systems are converted to distal gut neural deficiencies by the rostrocaudal migration pattern of the precursors. Fourth, we suggest that additional factors such as those found in serum and produced by the enteric neural cells themselves are likely also to be involved in enteric nervous system development and consequently in Hirschsprung's disease
Cell-Intrinsic Timers and Thyroid Hormone Regulate the Probability of Cell-Cycle Withdrawal and Differentiation of Oligodendrocyte Precursor Cells

AbstractDuring vertebrate development many types of precursor cells divide a limited number of times before they stop dividing and terminally differentiate. It is unclear what causes the cells to stop dividing when they do. We have been studying this problem in the oligodendrocyte cell lineage, which is responsible for myelination in the vertebrate central nervous system. Here we show for the first time that in clonal cultures of oligodendrocyte precursor cells purified from embryonic day 18 (E18) rat optic nerves the first oligodendrocytes develop within 3–4 days, equivalent to the time they first differentiate in the nerve, and that this timely differentiation depends on the presence of thyroid hormone. These findings suggest that a cell-intrinsic, thyroid-hormone-regulated timer determines when the first oligodendrocytes develop. Whereas the first oligodendrocytes develop asynchronously within clones, the vast majority develop after the first week in culture and do so more synchronously within clones. We show that β1 thyroid hormone receptors in the precursor cells increase in clonal cultures in the absence of thyroid hormone in parallel with the increasing sensitivity of the cells to the cell-cycle-arresting activity of thyroid hormone; moreover, the increase in β1 receptors, like the timer itself, is accelerated at 33°C compared to 37°C, suggesting that the increase in receptors may be part of the intrinsic timer. Finally, we show that the precursor cells do not divide indefinitely when stimulated to divide extensively in the absence of thyroid hormone but, instead, eventually stop dividing and either die or differentiate
Disregulation of Ocular Morphogenesis by Lens-Specific Expression of FGF-3/Int-2 in Transgenic Mice

AbstractFGF-3, originally named int-2, was discovered as an oncogene frequently activated in mammary carcinomas resulting from the chromosomal integration of the mouse mammary tumor virus (MMTV). Int-2 was later designated FGF-3 based on sequence homology with other members of the fibroblast growth factor (FGF) family. FGF-1 is the prototypical member of the FGF family, and is the only family member which activates all known FGF receptor isoforms. Transgenic mice expressing in the lens a form of FGF-1 engineered to be secreted show premature differentiation of the entire lens epithelium. In contrast, transgenic mice engineered to secrete FGF-2 in the lens do not undergo premature differentiation of the lens epithelium (C. M. Stolenet al.,1997,Development124, 4009–4017). To further assess the roles of FGFs and FGF receptors in lens development, the αA-crystallin promoter was used to target expression of FGF-3 to the developing lens of transgenic mice. The expression of FGF-3 in the lens rapidly induced epithelial cells throughout the lens to elongate and to express fiber cell-specific proteins including MIP and β-crystallins. This premature differentiation of the lens epithelium was followed by the degeneration of the entire lens. Since FGF-1 and FGF-3 can both activate one FGF receptor isoform (FGFR2 IIIb) that is not activated by FGF-2, these results suggest that activation of FGFR2 IIIb is sufficient to induce fiber cell differentiation throughout the lens epitheliumin vivo.Furthermore, transgenic lens cells expressing FGF-3 were able to induce the differentiation of neighboring nontransgenic lens epithelial cells in chimeric mice. Expression of FGF-3 in the lens also resulted in developmental alterations of the eyelids, cornea, and retina, and in the most severely affected transgenic lines, the postnatal appearance of intraocular glandular structures
In VivoRegulation of Cyclin A/Cdc2 and Cyclin B/Cdc2 through Meiotic and Early Cleavage Cycles in Starfish

AbstractIn starfish, fertilization occurs naturally at late meiosis I. In the absence of fertilization, however, oocytes complete meiosis I and II, resulting in mature eggs arrested at the pronucleus stage, which are still fertilizable. In this study, we isolated cDNAs of starfish cyclin A and Cdc2, and monitored extensively the cell cycle dynamics of cyclin A and cyclin B levels and their associated Cdc2 kinase activity, Tyr phosphorylation of Cdc2, and Cdc25 phosphorylation states throughout meiotic and early embryonic cleavage cyclesin vivo.In meiosis I, cyclin A was undetectable and cyclin B/Cdc2 alone exhibited histone H1 kinase activity, while thereafter both cyclin A/Cdc2 and cyclin B/Cdc2 kinase activity oscillated along with the cell cycle. Cyclin B-, but not cyclin A-, associated Cdc2 was subjected to regulation via Tyr phosphorylation, and phosphorylation states of Cdc25 correlated with cyclin B/Cdc2 kinase activity with some exceptions. Between meiosis I and II and at the pronucleus stage, cyclin A and B levels remained low, Cdc2 Tyr phosphorylation was undetectable, and Cdc25 remained phosphorylated depending on MAP kinase activity, showing a good correlation between these two stages. Upon fertilization of mature eggs, Cdc2 Tyr phosphorylation reappeared and Cdc25 was dephosphorylated. In the first cleavage cycle, under conditions which prevented Cdc25 activity, cyclin A/Cdc2 was activated with a normal time course and then cyclin B/Cdc2 was activated with a significant delay, resulting in the delayed completion of M-phase. Thus, in contrast to meiosis I, both cyclin A and cyclin B appear to be involved in the embryonic cleavage cycles. We propose that regulation of cyclin A/Cdc2 and cyclin B/Cdc2 is characteristic of meiotic and early cleavage cycles
Switching of Chemoattractant Receptors Programs Development and Morphogenesis inDictyostelium:Receptor Subtypes Activate Common Responses at Different Agonist Concentrations

AbstractOne of the common functional features among G-protein coupled receptors is the occurrence of multiple subtypes involved in similar signal transduction events. The cAMP chemoattractant receptor family ofDictyostelium discoideumis composed of four receptors (cAR1–cAR4), which are expressed sequentially throughout the developmental transition from a unicellular to a multicellular organism. The receptors differ in affinity for cAMP and in the sequences of their C-terminal domains. In this study, we constitutively expressed cAR1, cAR2, and cAR3 as well as a series of chimeric and mutant receptors and assessed the capacity of each to mediate chemotaxis, activation of adenylyl cyclase and actin polymerization, and rescue the developmental defect ofcar1−/car3−cells. We found that various receptors and mutants sense different concentration ranges of cAMP but all can mediate identical responses during the aggregation stage of development. The responses displayed very similar kinetics, suggesting no major differences in regulatory properties attributable to the C-terminal domains. We speculate that switching of receptor subtypes during development enables the organism to respond to the changing concentrations of the chemoattractant and thereby program morphogenesis appropriately
Additional Vegetative Growth in Maize Reflects Expansion of Fates in Preexisting Tissue, Not Additional Divisions by Apical Initials

AbstractThe maize shoot is usually determinate: the apical meristem produces a fixed number of vegetative nodes before it switches to tassel development. Culturing maize meristems, however, delays their determinacy. Cultured meristems may form up to twice the usual number of vegetative nodes. Clonal analysis of the “extra” vegetative nodes reveals that these nodes are the product of conversion, roughly equivalent to a homoeotic transformation, of tissue that otherwise would form the base of the tassel. Altered activity of the apical initials does not generate the extra vegetative growth. The conserved, stereotypical activity of the apical initials even in the face of radically prolonged vegetative growth suggests that apical initials in this annual grass may acquire a highly restricted fate (presporogenous tissue) early in embryogenesis
Overexpression of Zeste White 3 Blocks Wingless Signaling in theDrosophilaEmbryonic Midgut

AbstractThe extracellular signals encoded by the Wnt family of genes regulate growth and differentiation in several developmental processes in both vertebrates and invertebrates. Genetic studies of the signaling pathway of theDrosophilaWnt homologue, Wingless, have identified a number of genes, includingzeste white 3, which function to transduce the Wingless signal.zeste white 3encodes a serine/threonine kinase. We have previously proposed that the Wingless signal is mediated by repression of this kinase activity [E. Siegfried, E. L. Wilder, and N. Perrimon (1994)Nature367, 76–80]. Here we have tested this hypothesis by overexpressingzeste white 3in a tissue-specific fashion using the UAS/GAL4 binary expression system. We demonstrate that elevated levels ofzeste white 3in the ectoderm and mesoderm result in phenotypes that resemble a loss ofwingless. Overexpression ofzeste white 3in the mesoderm disrupts several Wingless-dependent processes including the specification of a unique cell type in the larval midgut, the formation of the second midgut constriction, and the expression of Wingless target genesUltrabithoraxanddecapentaplegicin the mesoderm andlabialin the endoderm. Zeste white 3 regulates the stability of Armadillo which is essential for transducing the Wingless signal to the nucleus. We show thatzeste white 3overexpression blocks Wingless signaling through the modulation of Armadillo since expression of a constitutively active form of Armadillo, which is independent of Zeste white 3 regulation, is epistatic to overexpression ofzeste white 3
Molecular Cloning and Characterization of Meichroacidin (Male Meiotic MetaphaseChromosome-AssociatedAcidic Protein)

AbstractWe have isolated a cDNA clone encoding a germ cell specific protein from an expression cDNA library prepared from the mouse testis, using testis-specific polyclonal antibodies. Sequence analysis of the cDNA revealed that the deduced amino acid sequence consisted of 284 residues, including a nominal repeat structure in the N-terminal region. Northern blot analysis revealed the presence of a transcript of 1.3 kb exclusively expressed in the testis and ovary, but at relatively low levels in the ovary. In contrast, no other tissues and organs expressed significant levels of the transcript. Expression of the mRNA in the testis was first detected on day 14 in postnatal development. Western blot analysis showed the presence of the protein with a molecular weight of approximately 40 kDa and an isoelectric point of 4.9. The protein was exclusively found in the testis and ovary, but in a far lesser amount in the ovary as was the case with the transcript. Immunohistochemical examination revealed that the protein was predominantly present in the cytoplasm in pachytene spermatocytes through to round spermatids. However, during the disappearance of the nuclear envelope at both the first and second meiotic divisions, the protein was localized around the metaphase chromosomes and spindles. Because of this, the name meichroacidin which stands formale meiotic metaphasechromosome-associatedacidic proteinis proposed for this antigen. The highly regulated stage-specific expression of meichroacidin and its specific association with the metaphase chromosomes and spindles suggest that the protein plays important roles in male meiosis
TheclocheandspadetailGenes Differentially Affect Hematopoiesis and Vasculogenesis

AbstractIn vertebrates, hematopoietic and vascular progenitors develop from ventral mesoderm. The first primitive wave of hematopoiesis yields embryonic red blood cells, whereas progenitor cells of subsequent definitive waves form all hematopoietic cell lineages. In this report we examine the development of hematopoietic and vasculogenic cells in normal zebrafish and characterize defects inclocheandspadetailmutant embryos. The zebrafish homologs oflmo2, c-myb, fli1, flk1, andflt4have been cloned and characterized in this study. Expression of these genes identifies embryonic regions that contain hematopoietic and vascular progenitor cells. The expression ofc-mybalso identifies definitive hematopoietic cells in the ventral wall of the dorsal aorta. Analysis ofb316mutant embryos that carry a deletion of thec-mybgene demonstrates thatc-mybis not required for primitive erythropoiesis in zebrafish even though it is expressed in these cells. Bothclocheandspadetailmutant embryos have defects in primitive hematopoiesis and definitive hematopoiesis. Theclochemutants also have significant decreases in vascular gene expression, whereasspadetailmutants expressed normal levels of these genes. These studies demonstrate that the molecular mechanisms that regulate hematopoiesis and vasculogenesis have been conserved throughout vertebrate evolution and thecloandsptgenes are key regulators of these programs