pinecone/core-2020-05-10-deduplication huggingface dataset:
Evidence That Phospholipase C from the Sperm Is Not Responsible for Initiating Ca2+ Release at Fertilization in Mouse Eggs

AbstractRelease of Ca2+ from intracellular stores at fertilization of mammalian eggs is mediated by inositol 1,4,5-trisphosphate (IP3), but the mechanism by which the sperm initiates IP3 production is not yet understood. We tested the hypothesis that phospholipase C (PLC) activity introduced into the mouse egg as a consequence of sperm–egg fusion is responsible for causing Ca2+ release. We demonstrated that microinjecting purified, recombinant PLCγ1 protein into mouse eggs caused Ca2+ oscillations like those seen at fertilization. However, the PLC activity in the minimum amount of purified PLCγ1 protein needed to elicit Ca2+ release when injected into eggs was ∼500–900 times the PLC activity contained in a single sperm. This indicates that a single mouse sperm does not contain enough PLC activity to be responsible for causing Ca2+ release at fertilization. We also examined whether phosphatidylinositol 3-kinase (PI3K) could have a role in this process, and found that several inhibitors of PI3K-mediated signaling had no effect on Ca2+ release at fertilization
A Population of Caudally Migrating Cranial Neural Crest Cells: Functional and Evolutionary Implications

AbstractThe deployment of the cranial neural crest is central to the patterning of the skeletomuscular elements of the vertebrate head, with cranial muscles invariably attaching to skeletal elements formed by crest from the same axial level. Here we demonstrate, through gene expression analysis, ablation studies and fate-mapping, the existence of a population of caudally migrating cranial crest that arise from the postotic neural tube. As with the rest of the postotic crest, these cells express the transcription factor Mafb, and this marker can be used to highlight their posterior migration. They pass out between the anterior somite and the otic vesicle, before turning caudally and running along the base of the somites. With long-term fate mapping, we show that these cells migrate to the clavicle and settle at the site of formation of the attachment point for the cleidohyoid muscle. As such, the influence of the cranial neural crest in organising skeletomuscular connectivity seems to extend beyond the head into the trunk. These results are of further importance as they help explain how, even though the pectoral girdle and the skull became physically dissociated during tetrapod evolution, skeletomuscular connectivity has been maintained
Overexpression of Smad2 Reveals Its Concerted Action with Smad4 in Regulating TGF- β-Mediated Epidermal Homeostasis

AbstractMembers of the transforming growth factor-β (TGF-β) superfamily are critical regulators for epithelial growth and can alter the differentiation of keratinocytes. Transduction of TGF-β signaling depends on the phosphorylation and activation of Smad proteins by heteromeric complexes of ligand-specific type I and II receptors. To understand the function of TGF-β and activin-specific Smad, we generated transgenic mice that overexpress Smad2 in epidermis under the control of keratin 14 promoter. Overexpression of Smad2 increases endogenous Smad4 and TGF-β1 expression while heterozygous loss of Smad2 reduces their expression levels, suggesting a concerted action of Smad2 and -4 in regulating TGF-β signaling during skin development. These transgenic mice have delayed hair growth, underdeveloped ears, and shorter tails. In their skin, there is severe thickening of the epidermis with disorganized epidermal architecture, indistinguishable basement membrane, and dermal fibrosis. These abnormal phenotypes are due to increased proliferation of the basal epidermal cells and abnormalities in the program of keratinocyte differentiation. The ectodermally derived enamel structure is also abnormal. Collectively, our study presents the first in vivo evidence that, by providing an auto-feedback in TGF-β signaling, Smad2 plays a pivotal role in regulating TGF-β-mediated epidermal homeostasis
Nodal Regulates Trophoblast Differentiation and Placental Development

AbstractNodal has been thought to be an embryo-specific factor that regulates development, but nodal is also expressed in the mouse placenta beginning at midgestation, specifically in the spongiotrophoblasts. In an insertional null nodal mutant, not only is embryonic development disrupted, but mouse placental development is also grossly altered with the loss of the diploid spongiotrophoblasts and labyrinth and an expansion of the polyploid giant cell layer. A hypomorphic mutation in nodal results in an expansion of the giant cell and spongiotrophoblast layers, and a decrease in labyrinthine development. Expression of nodal in trophoblast cell cultures is sufficient to inhibit trophoblast giant cell differentiation, demonstrating that nodal can act directly on trophoblasts. The mechanism of nodal action includes the inhibition of junB gene transcription. These results suggest that nodal may be involved in redirecting trophoblast fate towards the midgestational expansion of the labyrinth region while maintaining the thin layer of trophoblast giant cells and the underlying layer of spongiotrophoblasts that form the boundary between the maternal and extraembryonic compartments
A Possible Role for the Cnidarian Homologue of Serum Response Factor in Decision Making by Undifferentiated Cells

AbstractWe have isolated the serum response factor (SRF) homologue from two hydrozoans, the freshwater polyp Hydra vulgaris and the marine colonial Hydractinia echinata; we have termed the Hydra gene HvSRF and the Hydractinia gene HeSRF. The MADS-box of both genes is identical in sequence and more similar to SRFs of other organisms than to non-SRF MADS-box-containing proteins from other organisms. Within the N terminus of the predicted protein, a motif of 14 amino acids is nearly identical between Hydra and Hydractinia. This motif is absent from other known SRF sequences. In the adult Hydra polyp, SRF is predominantly expressed in cells of the interstitial cell (I-cell) lineage. Expression of SRF ceases when I-cells differentiate into nerve cells, nematocytes, or gland cells. In the course of sexual reproduction in Hydractinia, SRF is expressed in female germ cells. During embryogenesis, SRF transcripts are observed in all blastomeres. Later on, SRF expression is turned off in cells forming the ectodermal layer but further on is expressed in cells of the central cell mass, from which the endodermal epithelial cells and the I-cell lineage originate. Expression eventually becomes restricted to the I-cell lineage. We conclude that hydrozoan SRF is expressed in all these cells, which still have the property for differentiation. In adult Hydra, the abundance of SRF transcripts varies during the day. The pacemaker of this diurnal rhythm is the feeding regime. HvSRF expression decreases by 4 h after feeding and returns to the initial level 12 h after feeding. When feeding is stopped, the cycle of SRF expression persists through the first day when the animals are not fed. It has been shown that feeding partly synchronizes the cell cycle of the epithelial cells but not that of the I-cells. We suggest that the epithelial cells affect SRF expression in I-cells and thereby influence the decision of I-cells to enter a differentiation pathway
Fertilization Blocks Apoptosis of Starfish Eggs by Inactivation of the MAP Kinase Pathway

AbstractFully grown starfish oocytes are arrested at prophase of meiosis I. The hormonal stimulation of 1-methyladenine (1-MA) induces meiosis reinitiation and germinal vesicle breakdown (GVBD). Optimal development occurs when maturing oocytes are fertilized between GVBD and first polar body emission. In the absence of sperm, oocytes complete both meiotic divisions to yield haploid interphase-arrested eggs. We now report that spontaneous and synchronous activation of caspase-3 in starfish eggs occurs 9–12 h after 1-MA stimulation. Then, caspase-dependent membrane blebbing and egg fragmentation occur, indicating that mature eggs undergo apoptosis if not fertilized. Activation of caspase-3 and induction of apoptosis are blocked both by a MEK inhibitor and by emetine treatment which inhibits MEK kinase (Mos) synthesis. Conversely, when recombinant GST-Mos is injected into the emetine-treated eggs, apoptosis is induced. These results indicate that persistent activation of the Mos/MEK/MAP kinase cascade gives the death-activating signal in starfish eggs. Fertilization inactivates the MAP kinase pathway and suppresses apoptosis, followed by normal development
Regulation of MAP Kinase by the BMP-4/TAK1 Pathway in Xenopus Ectoderm

AbstractBone morphogenetic protein-4 (BMP-4) induces epidermis and represses neural fate in Xenopus ectoderm. Our previous findings implicate p42 Erk MAP kinase (MAPK) in the response to neural induction. We have examined the effects of BMP-4 on MAPK activity in gastrula ectoderm. Expression of a dominant negative BMP-4 receptor resulted in a 4.5-fold elevation in MAPK activity in midgastrula ectoderm. MAPK activity was reduced in ectoderm expressing a constitutively active BMP-4 receptor, or ectoderm treated with BMP-4 protein in the presence or absence of cycloheximide. Overexpression of TAK1 led to a reduction in MAPK activity in early gastrula ectoderm. The inhibitory effects of TAK1 could be reversed by 1 μM SB 203580, a p38 inhibitor. Treatment of isolated ectoderm with SB 203580 led to expression of otx2, NCAM, and noggin. Western blot analyses indicated that the BMP-4 pathway does not activate JNKs in ectoderm. Our findings indicate that BMP-4 inhibits ectodermal MAPK activity through a TAK1/p38-type pathway. MAPK has been shown to inactivate Smad1. Thus, our results suggest that BMP-4 and MAPK pathways are mutually antagonistic in Xenopus ectoderm, and that interactions between these pathways may govern the choice between epidermal and neural fate
The BMP/CHORDIN Antagonism Controls Sensory Pigment Cell Specification and Differentiation in the Ascidian Embryo

AbstractWe have investigated the role of the bone morphogenetic protein (BMP) pathway during neural tissue formation in the ascidian embryo. The orthologue of the BMP antagonist, chordin, was isolated from the ascidian Halocynthia roretzi. While both the expression pattern and the phenotype observed by overexpressing chordin or BMPb (the dpp-subclass BMP) do not suggest a role for these factors in neural induction, BMP/CHORDIN antagonism was found to affect neural patterning. Overexpression of BMPb induced ectopic sensory pigment cells in the brain lineages that do not normally form pigment cells and suppressed pressure organ formation within the brain. Reciprocally, overexpressing chordin suppressed pigment cell formation and induced ectopic pressure organ. We show that pigment cell formation occurs in three steps. (1) During cleavage stages ectodermal cells are neuralized by a vegetal signal that can be substituted by bFGF. (2) At the early gastrula stage, BMPb secreted from the lateral nerve cord blastomeres induces those neuralized blastomeres in close proximity to adopt a pigment cell fate. (3) At the tailbud stage, among these pigment cell precursors, BMPb induces the differentiation of specifically the anterior type of pigment cell, the otolith; while posteriorly, CHORDIN suppresses BMP activity and allows ocellus differentiation
Boundaries and Functional Domains in the Animal/Vegetal Axis of Xenopus Gastrula Mesoderm

AbstractPatterning of the Xenopus gastrula marginal zone in the axis running equatorially from the Spemann organizer—the so-called “dorsal/ventral axis”—has been extensively studied. It is now evident that patterning in the animal/vegetal axis also needs to be taken into consideration. We have shown that an animal/vegetal pattern is apparent in the marginal zone by midgastrulation in the polarized expression domains of Xenopusbrachyury (Xbra) and Xenopusnodal-related factor 2 (Xnr2). In this report, we have followed cells expressing Xbra in the presumptive trunk and tail at the gastrula stage, and find that they fate to presumptive somite, but not to ventrolateral mesoderm of the tailbud embryo. From this, we speculate that the boundary between the Xbra- and Xnr2-expressing cells at gastrula corresponds to a future tissue boundary. In further experiments, we show that the level of mitogen-activated protein kinase (MAPK) activation is polarized along the animal/vegetal axis, with the Xnr2-expressing cells in the vegetal marginal zone having no detectable activated MAPK. We show that inhibition of MAPK activation in Xenopus animal caps results in the conversion of Xnr2 from a dorsal mesoderm inducer to a ventral mesoderm inducer, supporting a role for Xnr2 in induction of ventral mesoderm
Hoxa3 and Pax1 Regulate Epithelial Cell Death and Proliferation during Thymus and Parathyroid Organogenesis

AbstractThe thymus and parathyroid glands in mice develop from a thymus/parathyroid primordium that forms from the endoderm of the third pharyngeal pouch. We investigated the molecular mechanisms that promote this unique process in which two distinct organs form from a single primordium, using mice mutant for Hoxa3 and Pax1. Thymic ectopia in Hoxa3+/−Pax1−/− compound mutants is due to delayed separation of the thymus/parathyroid primordium from the pharynx. The primordium is hypoplastic at its formation, and has increased levels of apoptosis. The developing third pouch in Hoxa3+/−Pax1−/− compound mutants initiates normal expression of the parathyroid-specificGcm2 and thymus-specific Foxn1 genes. However, Gcm2 expression is reduced at E11.5 in Pax1−/− single mutants, and further reduced or absent in Hoxa3+/−Pax1−/− compound mutants. Subsequent to organ-specific differentiation from the shared primordium, both the parathyroids and thymus developed defects. Parathyroids in compound mutants were smaller at their formation, and absent at later stages. Parathyroids were also reduced in Pax1−/− mutants, revealing a new function forPax1 in parathyroid organogenesis. Thymic hypoplasia at later fetal stages in compound mutants was associated with increased death and decreased proliferation of thymic epithelial cells. Our results suggest that a Hoxa3–Pax1 genetic pathway is required for both epithelial cell growth and differentiation throughout thymus and parathyroid organogenesis
Guinea Pig Fertilin Exhibits Restricted Lateral Mobility in Epididymal Sperm and Becomes Freely Diffusing during Capacitation

AbstractThe guinea pig sperm protein fertilin functions in sperm–egg plasma membrane binding. Fertilin is initially present in the plasma membrane of the whole head in testicular sperm, then becomes concentrated into the posterior head domain during epididymal passage. Fertilin remains localized to the posterior head plasma membrane following the acrosome reaction, when it functions in sperm–egg interaction. Fluorescence redistribution after photobleaching was used to examine the lateral mobility of fertilin in both acrosome-intact and acrosome-reacted sperm. Fertilin exhibited highly restricted lateral mobility in both testicular and epididymal sperm (D < 10−10 cm2/s). However, fertilin in acrosome-reacted sperm was highly mobile within the membrane bilayer (D = 1.8 × 10−9 cm2/s and %R = 84). Measurement of the lateral mobility of fertilin in capacitated, acrosome-intact sperm revealed two populations of cells. In approximately one-half of the cells, lateral mobility of fertilin was similar to sperm freshly isolated from the cauda epididymis; while in the other half fertilin was highly mobile. The release of fertilin from interactions that restrict its lateral mobility may regulate its function in sperm–egg interaction
Msx-2 and p21 Mediate the Pro-Apoptotic but Not the Anti-Proliferative Effects of BMP4 on Cultured Sympathetic Neuroblasts

AbstractThe differentiation, survival, and proliferation of developing sympathetic neuroblasts are all coordinately promoted by neurotrophins. In this study, we demonstrate that bone morphogenetic protein 4 (BMP4), a factor known to be necessary for the differentiation of sympathetic neurons (Schneider et al., 1999), conversely reduces both survival and proliferation of cultured E14 sympathetic neuroblasts. The anti-proliferative effects of BMP4 occur more rapidly than the pro-apoptotic actions and appear to involve different intracellular mechanisms. BMP4 treatment induces expression of the transcription factor Msx-2 and the cyclin-dependent kinase inhibitor p21CIP1/WAF1 (p21). Treatment of cells with oligonucleotides antisense to either of these genes prevents cell death after BMP4 treatment but does not significantly alter the anti-proliferative effects. Thus Msx-2 and p21 are necessary for BMP4-mediated cell death but not for promotion of exit from cell cycle. Although treatment of cultured E14 sympathetic neuroblasts with neurotrophins alone did not alter cell numbers, BMP4-induced cell death was prevented by co-treatment with either neurotrophin-3 (NT-3) or nerve growth factor (NGF). This suggests that BMP4 may also induce dependence of the cells on neurotrophins for survival. Thus, sympathetic neuron numbers may be determined in part by factors that inhibit the proliferation and survival of neuroblasts and make them dependent upon exogenous factors for survival
Genetic Dissection of the Drosophila Cubitus interruptus Signaling Complex

AbstractMuch of our understanding of the Hedgehog (Hh) signaling pathway comes from Drosophila, where a gradient of Hh signaling regulates the function of the transcription factor Cubitus interruptus (Ci) at three levels: protein stabilization, nuclear import, and activation. Regulation of Ci occurs in a cytoplasmic complex containing Ci, the kinesin-like protein Costal-2 (Cos2), the serine-threonine kinase Fused (Fu), and the Suppressor of Fused [Su(fu)] protein. The mechanisms by which this complex responds to different levels of Hh signaling and establishes distinct domains of gene expression are not fully understood. By sequentially mutating components from the Ci signaling complex, their roles in each aspect of Ci regulation can be analyzed. The Cos2-Ci core complex is able to mediate Hh-regulated activation of Ci but is insufficient to regulate nuclear import and cleavage. Addition of Su(fu) to the core complex blocks nuclear import while the addition of Fu restores Hh regulation of Ci nuclear import and proteolytic cleavage. Fu participates in two partially redundant pathways to regulate Ci nuclear import; the kinase function plays a positive role by inhibiting Su(fu), and the regulatory domain plays a negative role in conjunction with Cos2
Manifestation of the Limb Prepattern: Limb Development in the Absence of Sonic Hedgehog Function

AbstractThe secreted protein encoded by the Sonic hedgehog (Shh) gene is localized to the posterior margin of vertebrate limb buds and is thought to be a key signal in establishing anterior–posterior limb polarity. In the Shh−/− mutant mouse, the development of many embryonic structures, including the limb, is severely compromised. In this study, we report the analysis of Shh−/− mutant limbs in detail. Each mutant embryo has four limbs with recognizable humerus/femur bones that have anterior–posterior polarity. Distal to the elbow/knee joints, skeletal elements representing the zeugopod form but lack identifiable anterior–posterior polarity. Therefore, Shh specifically becomes necessary for normal limb development at or just distal to the stylopod/zeugopod junction (elbow/knee joints) during mouse limb development. The forelimb autopod is represented by a single distal cartilage element, while the hindlimb autopod is invariably composed of a single digit with well-formed interphalangeal joints and a dorsal nail bed at the terminal phalanx. Analysis of GDF5 and Hoxd11–13 expression in the hindlimb autopod suggests that the forming digit has a digit-one identity. This finding is corroborated by the formation of only two phalangeal elements which are unique to digit one on the foot. The apical ectodermal ridge (AER) is induced in the Shh−/− mutant buds with relatively normal morphology. We report that the architecture of the Shh−/− AER is gradually disrupted over developmental time in parallel with a reduction of Fgf8 expression in the ridge. Concomitantly, abnormal cell death in the Shh−/− limb bud occurs in the anterior mesenchyme of both fore- and hindlimb. It is notable that the AER changes and mesodermal cell death occur earlier in the Shh−/− forelimb than the hindlimb bud. This provides an explanation for the hindlimb-specific competence to form autopodial structures in the mutant. Finally, unlike the wild-type mouse limb bud, the Shh−/− mutant posterior limb bud mesoderm does not cause digit duplications when grafted to the anterior border of chick limb buds, and therefore lacks polarizing activity. We propose that a prepattern exists in the limb field for the three axes of the emerging limb bud as well as specific limb skeletal elements. According to this model, the limb bud signaling centers, including the zone of polarizing activity (ZPA) acting through Shh, are required to elaborate upon the axial information provided by the native limb field prepattern
Endoderm Specification and Differentiation in Xenopus Embryos

AbstractIt is known from work with amniote embryos that regional specification of the gut requires cell–cell signalling between the mesoderm and the endoderm. In recent years, much of the interest in Xenopus endoderm development has focused on events that occur before gastrulation and this work has led to a different model whereby regional specification of the endoderm is autonomous. In this paper, we examine the specification and differentiation of the endoderm in Xenopus using neurula and tail-bud-stage embryos and we show that the current hypothesis of stable autonomous regional specification is not correct. When the endoderm is isolated alone from neurula and tail bud stages, it remains fully viable but will not express markers of regional specification or differentiation. If mesoderm is present, regional markers are expressed. If recombinations are made between mesoderm and endoderm, then the endodermal markers expressed have the regional character of the mesoderm. Previous results with vegetal explants had shown that endodermal differentiation occurs cell-autonomously, in the absence of mesoderm. We have repeated these experiments and have found that the explants do in fact show some expression of mesoderm markers associated with lateral plate derivatives. We believe that the formation of mesoderm cells by the vegetal explants accounts for the apparent autonomous development of the endoderm. Since the fate map of the Xenopus gut shows that the mesoderm and endoderm of each level do not come together until tail bud stages, we conclude that stable regional specification of the endoderm must occur quite late, and as a result of inductive signals from the mesoderm