pinecone/core-2020-05-10-deduplication huggingface dataset:
Hsp25 and the p38 MAPK Pathway Are Involved in Differentiation of Cardiomyocytes

AbstractThe small heat-shock protein HSP25 is expressed in the heart early during development, and although multiple roles for HSP25 have been proposed, its specific role during development and differentiation is not known. P19 is an embryonal carcinoma cell line which can be induced to differentiate in vitro into either cardiomyocytes or neurons. We have used P19 to examine the role of HSP25 in differentiation. We found that HSP25 expression is strongly increased in P19 cardiomyocytes. Antisense HSP25 expression reduced the extent of cardiomyocyte differentiation and resulted in reduced expression of cardiac actin and the intermediate filament desmin and reduced level of cardiac mRNAs. Thus, HSP25 is necessary for differentiation of P19 into cardiomyocytes. In contrast, P19 neurons did not express HSP25 and antisense HSP25 expression had no effect on neuronal differentiation. The phosphorylation of HSP25 by the p38/SAPK2 pathway is known to be important for certain of its functions. Inhibition of this pathway by the specific inhibitor SB203580 prevented cardiomyocyte differentiation of P19 cells. In contrast, PD90589, which inhibits the ERK1/2 pathway, had no effect. Surprisingly, cardiogenesis was only sensitive to SB203580 during the first 2 days of differentiation, before HSP25 expression increases. In contrast to the effect of antisense HSP25, SB203580 reduced the level of expression of the mesodermal marker Brachyury-T during differentiation. Therefore, we propose that the p38 pathway acts on an essential target during early cardiogenesis. Once this initial step is complete, HSP25 is necessary for the functional differentiation of P19 cardiomyocytes, but its phosphorylation by p38/SAPK2 is not required
A 130-kDa Membrane Protein of Sperm Flagella Is the Receptor for Asterosaps, Sperm-Activating Peptides of Starfish Asterias amurensis

AbstractSpermatozoa of the starfish, Asterias amurensis, have a specific receptor for asterosap, a sperm-activating peptide isolated from the jelly coat of homologous eggs. We characterized the receptor by using several asterosap derivatives. Analysis of equilibrium binding of radioactive di-iodinated Bolton–Hunter reagent-labeled asterosap (125I2-BHP15) to the spermatozoa indicated that the cell has 1.1 × 105 binding sites of high affinity (Kd = 57 pM), and also the receptor showed positive cooperativity for asterosap binding. When spermatozoa were treated with fluorophore-labeled asterosap, the sperm flagella were labeled, indicating that the receptors are mostly localized in the sperm tail. When spermatozoa were reacted with radioactive asterosap prelabeled with photoaffinity cross-linkers, a single 130-kDa membrane protein of sperm flagella was specifically radiolabeled. This result was reproducible regardless of the length of spacer arm of cross-linkers so far studied. Therefore, the 130-kDa protein is likely to be the receptor for asterosaps. Modification of asterosap at the N-terminal region with bulky molecules such as carboxyfluorescein did not affect the activity of asterosap, suggesting that the N-terminus of asterosap is not involved in the ligand–receptor interaction. On the other hand, S-alkylated asterosaps did not compete with 125I2-BHP15 for binding to the receptor, indicating that disulfide linkage of asterosap is essential for the ligand–receptor interaction. The properties of the receptor, high affinity and high concentration, enabled us to apply the fluorescence polarization technique to study the molecular interaction between asterosap and the receptor. Using this method, we performed binding experiments in almost real time and found that divalent cations are significantly involved in the interaction between asterosap and the receptor
Anterior Endoderm Is Sufficient to Rescue Foregut Apoptosis and Heart Tube Morphogenesis in an Embryo Lacking Retinoic Acid

AbstractThe vitamin A deficient (VAD) quail embryo lacks active retinoids, fails to express normally GATA-4, and develops a nonlooping heart tube morphogenetic defect that is a model for congenital cardiomyopathy. VAD quail embryos, or chick embryos depleted specifically for GATA factors, show in addition abnormal foregut development, characterized by apoptosis of the endoderm cells associated with presumptive myocardium during the process of heart tube formation. Exogenous retinoic acid or transplantation of normal chick embryo anterior endoderm is sufficient to rescue apoptosis as well as GATA-4 expression and results in normal development and heart tube morphogenesis. Normal posterior endoderm also contains retinoids but is unable to rescue the VAD defect. Our results indicate that a retinoid-dependent transcriptional program, mediated at least in part by GATA factors, is critical in presumptive foregut endoderm for normal heart tube morphogenesis
Analyses of Segment-Specific Expression of Alkaline Phosphatase Activity in the Mesoderm of the Oligochaete Annelid Tubifex: Implications for Specification of Segmental Identity

AbstractIn the embryos of the oligochaete annelid Tubifex, segments VII and VIII specifically express mesodermal alkaline phophatase (ALP) activity in the ventrolateral region. In this study, we examined whether this segment-specific expression of ALP activity depends on external cues. Cell lineage analyses show that the ALP-expressing cells originate from M teloblasts. Furthermore, a set of teloblast-ablation experiments demonstrated that the seventh and eighth primary m blast cells (m7 and m8) produced from M teloblasts give rise to ALP-expressing cells in segments VII and VIII, respectively, and that primary m blast cells other than m7 and m8 lack the ability to generate ALP-expressing progeny cells. The results of another set of blastomere-ablation experiments suggest that ALP-expressing cells emerge independently of interactions with surrounding tissues. Teloblast-transplantation experiments demonstrated that m8 can generate ALP-expressing cells in an ectopical position, suggesting that it is unlikely that ALP activity emerges in response to the positional cues residing in the embryo. These results suggest that m7 and m8 are exclusively specified as precursors of ALP-expressing cells at the time of their birth from M teloblasts. We propose that segmental identities in primary m blast cells of the Tubifex embryo are determined according to the genealogical position in the M lineage and that the M teloblast possesses a developmental program through which the sequence of blast cell identities is determined
Genetic Analysis of Bristle Loss in Hybrids between Drosophila melanogaster and D. simulans Provides Evidence for Divergence of cis-Regulatory Sequences in the achaete–scute Gene Complex

AbstractThe two closely related species of Drosophila, D. melanogaster and D. simulans, display an identical bristle pattern on the notum, but hybrids between the two are lacking a variable number of bristles. We show that the loss is temperature-dependent and provide evidence for two periods of temperature sensitivity. A first period of heat sensitivity occurs during larval development and corresponds to the time when the prepattern of expression of genes whose products activate achaete–scute in the proneural clusters preceding bristle precursor formation is established. A second period of cold sensitivity corresponds to the time of emergence of the bristle precursor cells and the maintenance of their neural fate, a process requiring high levels of Achaete–Scute. Expression of achaete–scute at these two critical periods depends on cis-regulatory elements of the achaete–scute complex (AS-C). The differences between males, which have only one copy of the X-linked AS-C from D. simulans, and females, which have copies from both parental species, are compared, together with the effects of crossing in different rearrangements of the D. melanogaster AS-C that delete regulatory and/or coding sequences. We provide evidence that bristle loss in the hybrids may result from a decrease in the level of transcription at the AS-C and argue that interaction between trans-acting factors and cis-regulatory elements within the AS-C has diverged between the two species
GDNF Is a Chemoattractant for Enteric Neural Cells

AbstractIn situ hybridization revealed that GDNF mRNA in the mid- and hindgut mesenchyme of embryonic mice was minimal at E10.5 but was rapidly elevated at all gut regions after E11, but with a slight delay (0.5 days) in the hindgut. GDNF mRNA expression was minimal in the mesentery and in the pharyngeal and pelvic mesenchyme adjacent to the gut. To examine the effect of GDNF on enteric neural crest-derived cells, segments of E11.5 mouse hindgut containing crest-derived cells only at the rostral ends were attached to filter paper supports and grown in catenary organ culture. With GDNF (100 ng/ml) in the culture medium, threefold fewer neurons developed in the gut explants and fivefold more neurons were present on the filter paper outside the gut explants, compared to controls. Thus, in controls, crest-derived cells colonized the entire explant and differentiated into neurons, whereas in the presence of exogenous GDNF, most crest-derived cells migrated out of the gut explant. This is consistent with GDNF acting as a chemoattractant. To test this idea, explants of esophagus, midgut, superior cervical ganglia, paravertebral sympathetic chain ganglia, or dorsal root ganglia from E11.5–E12.5 mice were grown on collagen gels with a GDNF-impregnated agarose bead on one side and a control bead on the opposite side. Migrating neural cells and neurites from the esophagus and midgut accumulated around the GDNF-impregnated beads, but neural cells in other tissues showed little or no chemotactic response to GDNF, although all showed GDNF-receptor (Ret and GFRα1) immunoreactivity. We conclude that GDNF may promote the migration of crest cells throughout the gastrointestinal tract, prevent them from straying out of the gut (into the mesentery and pharyngeal and pelvic tissues), and promote directed axon outgrowth
Spatial and Temporal Patterns of Cell Division during Early Xenopus Embryogenesis

AbstractWe describe the spatial and temporal patterns of cell division in the early Xenopus embryo, concentrating on the period between the midblastula transition and the early tailbud stage. Mitotic cells were identified using an antibody recognising phosphorylated histone H3. At least four observations are of interest. First, axial mesodermal cells, including prospective notochord, stop dividing after involution and may not divide thereafter. Second, cell division is more pronounced in the neural plate than in nonneural ectoderm, and the pattern of cell division becomes further refined as neurogenesis proceeds. Third, cells in the cement gland cease proliferation completely as they begin to accumulate pigment. Finally, the precursors of peripheral sensory organs such as the ear and olfactory placode undergo active cell proliferation when they arise from the sensorial layer of the ectoderm. These observations and others should provide a platform to study the relationship between the regulation of developmental processes and the cell cycle during Xenopus embryogenesis
Trophoblast Giant-Cell Differentiation Involves Changes in Cytoskeleton and Cell Motility

AbstractTrophoblast giant-cell differentiation is well-characterized at the molecular level, yet very little is known about how molecular changes affect the cellular functions of trophoblast in embryo implantation. We have found, using both explanted E7.5 mouse embryo ectoplacental cone and the rat choriocarcinoma (Rcho-1) cell line, that trophoblast differentiation is distinguished by dramatic changes in cytoarchitecture and cell behavior. Undifferentiated trophoblast cells contain little organized actin and few small, peripheral focal complexes and exhibit high membrane protrusive activity, while differentiated trophoblast giant cells contain prominent stress fibers, large internal as well as peripheral focal adhesions, and become immotile. The dramatic changes in cell behavior and cytoskeletal organization of giant cells correlate with changes in the activities of the Rho family of small GTPases and a decrease in tyrosine phosphorylation of focal adhesion kinase. Together, these data provide detailed insight into the cellular properties of trophoblast giant cells and suggest that giant-cell differentiation is characterized by a transition from a motile to a specialized epithelial phenotype. Furthermore, our data support a phagocytic erosion, rather than a migratory infiltration, mechanism for trophoblast giant-cell invasion of the uterine stroma
Expression of Hoxb13 and Hoxc10 in Developing and Regenerating Axolotl Limbs and Tails

AbstractThe expression of Hox complex genes in correct spatial and temporal order is critical to patterning of the body axis and limbs during embryonic development. In order to understand the role such genes play in appendage regeneration, we have compared the expression of two 5′ Hox complex genes: Hoxb13 and Hoxc10 during development and regeneration of the body axis and the limbs of axolotls. In contrast to higher vertebrates, Hoxb13 is expressed not only in the tip of the developing tail, but also in the distal mesenchyme of developing hind limbs, and at low levels in developing forelimbs. Hoxc10 is expressed as two transcripts during both development and regeneration. The short transcript (Hoxc10S) is expressed in the tip of the developing tail, in developing hind limbs, and at low levels in developing forelimbs. The long transcript (Hoxc10L) is expressed in a similar pattern, with the exception that no expression in developing forelimbs could be detected. Hoxb13 and both transcripts of Hoxc10 are expressed at high levels in the regenerating spinal cord during tail regeneration, and in both regenerating hind limbs and forelimbs. The up-regulation of expression of these genes during forelimb regeneration, relative to the very low levels of expression during forelimb development, suggests that they play a critical and perhaps unique role in regeneration. This is particularly true for Hoxc10L, which is not expressed during forelimb development, but is expressed during forelimb regeneration; thus making it the first truly “regeneration-specific” gene transcript identified to date
Overexpression of a Slit Homologue Impairs Convergent Extension of the Mesoderm and Causes Cyclopia in Embryonic Zebrafish

AbstractSlit is expressed in the midline of the central nervous system both in vertebrates and invertebrates. In Drosophila, it is the midline repellent acting as a ligand for the Roundabout (Robo) protein, the repulsive receptor which is expressed on the growth cones of the commissural neurons. We have isolated cDNA fragments of the zebrafish slit2 and slit3 homologues and found that both genes start to be expressed by the midgastrula stage well before the axonogenesis begins in the nervous system, both in the axial mesoderm, and slit2 in the anterior margin of the neural plate and slit3 in the polster at the anterior end of the prechordal mesoderm. Later, expression of slit2 mRNA is detected mainly in midline structures such as the floor plate cells and the hypochord, and in the anterior margins of the neural plates in the zebrafish embryo, while slit3 expression is observed in the anterior margin of the prechordal plate, the floorplate cells in the hindbrain, and the motor neurons both in the hindbrain and the spinal cord. To study the role of Slit in early embryos, we overexpressed Slit2 in the whole embryos either by injection of its mRNA into one-cell stage embryos or by heat-shock treatment of the transgenic embryos which carries the slit2 gene under control of the heat-shock promoter. Overexpression of Slit2 in such ways impaired the convergent extension movement of the mesoderm and the rostral migration of the cells in the dorsal diencephalon and resulted in cyclopia. Our results shed light on a novel aspect of Slit function as a regulatory factor of mesodermal cell movement during gastrulation
Tie2-Cre Transgenic Mice: A New Model for Endothelial Cell-Lineage Analysis in Vivo

AbstractEndocardial cells are thought to contribute at least in part to the formation of the endocardial cushion mesenchyme. Here, we created Tie2-Cre transgenic mice, in which expression of Cre recombinase is driven by an endothelial-specific promoter/enhancer. To analyze the lineage of Cre expressing cells, we used CAG-CAT-Z transgenic mice, in which expression of lacZ is activated only after Cre-mediated recombination. We detected pan-endothelial expression of the Cre transgene in Tie2-Cre;CAG-CAT-Z double-transgenic mice. This expression pattern is almost identical to Tie2-lacZ transgenic mice. However, interestingly, we observed strong and uniform lacZ expression in mesenchymal cells of the atrioventricular canal of Tie2-Cre;CAG-CAT-Z double-transgenic mice. We also detected lacZ expression in the mesenchymal cells in part of the proximal cardiac outflow tract, but not in the mesenchymal cells of the distal outflow tract and branchial arch arteries. LacZ staining in Tie2-Cre;CAG-CAT-Z embryos is consistent with endocardial–mesenchymal transformation in the atrioventricular canal and outflow tract regions. Our observations are consistent with previously reported results from Cx43-lacZ, Wnt1-Cre;R26R, and Pax3-Cre;R26R transgenic mice, in which lacZ expression in the cardiac outflow tract identified contributions in part from the cardiac neural crest. Tie2-Cre transgenic mice are a new genetic tool for the analyses of endothelial cell-lineage and endothelial cell–specific gene targeting
Ephrin-A6, a New Ligand for EphA Receptors in the Developing Visual System

AbstractIn the embryonic visual system, EphA receptors are expressed on both temporal and nasal retinal ganglion cell axons. Only the temporal axons, however, are sensitive to the low concentrations of ephrin-A ligands found in the anterior optic tectum. The poor responsiveness of nasal axons to ephrin-A ligands, which allows them to traverse the anterior tectum and reach their targets in the posterior tectum, has been attributed to constitutive activation of the EphA4 receptor expressed in these axons. EphA4 is highly expressed throughout the retina, but is preferentially phosphorylated on tyrosine (activated) in nasal retina. In a screen for EphA4 ligands expressed in chicken embryonic retina, we have identified a novel ephrin, ephrin-A6. Like ephrin-A5, ephrin-A6 has high affinity for EphA4 and activates this receptor in cultured retinal cells. In the embryonic day 8 (E8) chicken visual system, ephrin-A6 is predominantly expressed in the nasal retina and ephrin-A5 in the posterior tectum. Thus, ephrin-A6 has the properties of a ligand that activates the EphA4 receptor in nasal retinal cells. Ephrin-A6 binds with high affinity to several other EphA receptors as well and causes growth cone collapse in retinal explants, demonstrating that it can elicit biological responses in retinal neurons. Ephrin-A6 expression is high at E6 and E8, when retinal axons grow to their tectal targets, and gradually declines at later developmental stages. The asymmetric distribution of ephrin-A6 in retinal cells, and the time course of its expression, suggest that this new ephrin plays a role in the establishment of visual system topography
Patterns of Cell Division and Expression of Asymmetric Cell Fate Determinants in Postembryonic Neuroblast Lineages of Drosophila

AbstractWe have studied the division of postembryonic neuroblasts (Nbs) in the outer proliferation center (OPC) and central brain anlagen of Drosophila. We focused our attention on three aspects of these processes: the pattern of cellular division, the topological orientation of those divisions, and the expression of asymmetric cell fate determinants. Although larval Nbs are of embryonic origin, our results indicate that their properties appear to be modified during development. Several conclusions can be summarized: (i) In early larvae, Nbs divide symmetrically to give rise to two Nbs while in the late larval brain most Nbs divide asymmetrically to bud off an intermediate ganglion mother cell (GMC) that very rapidly divides into two ganglion cells (GC). (ii) Symmetric and asymmetric divisions of OPC Nbs show tangential and radial orientations, respectively. (iii) This change in the pattern of division correlates with the expression of inscuteable, which is apically localized only in asymmetric divisions. (iv) The spindle of asymmetrically dividing Nb is always oriented on an apical–basal axis. (v) Prospero does not colocalize with Miranda in the cortical crescent of mitotic Nbs. (vi) Prospero is transiently expressed in one of the two sibling GCs generated by the division of GMCs. The implications of these results on cell fate specification and differentiation of adult brain neurons are discussed
The Amino Terminus of Smads Permits Transcriptional Specificity

AbstractSmad proteins transduce transforming growth factor-β signals from the cell surface to the nucleus, regulating a variety of physiologic processes. In the nucleus, Smads control gene expression by binding to both DNA and transcription factors. Individual Smads regulate distinct subsets of target genes. The key residues important for this specificity are thought to reside in the carboxyl-terminal MH2 domain. To further examine Smad specificity in vivo, we undertook structure-function studies in Xenopus laevis embryos and found that truncated Smads containing the MH2 domain activate gene transcription. A striking finding revealed by the in vivo analyses was that the functional truncated Smads all behaved identically and had lost wild-type specificity. For most Smads, wild-type activity required the presence of an MH1 domain, either in cis or in trans. Of note, even heterologous MH1 domains could restore wild-type signaling specificity to effector MH2 domains. We found a possible mechanism to account for these observations, as Smad MH1 domains altered the binding of pathway-specific transcription factors to the MH2 domain. Thus, Smad MH1 domains are important to the regulation of transcriptional specificity