pinecone/core-2020-05-10-deduplication huggingface dataset:
Epithelial Cell Wedging and Neural Trough Formation Are Induced Planarly inXenopus,without Persistent Vertical Interactions with Mesoderm

AbstractIn this study we investigate the induction of the cell behaviors underlying neurulation in the frog,Xenopus laevis.Although planar signals from the organizer can induce convergent extension movements of the posterior neural tissue in explants, the remaining morphogenic processes of neurulation do not appear to occur in absence of vertical interactions with the organizer (R. Kelleret al.,1992,Dev. Dyn.193, 218–234). These processes include: (1) cell elongation perpendicular to the plane of the epithelium, forming the neural plate; (2) cell wedging, which rolls the neural plate into a trough; (3) intercalation of two layers of neural plate cells to form one layer; and (4) fusion of the neural folds. To allow planar signaling between all the inducing tissues of the involuting marginal zone and the responding prospective ectoderm, we have designed a “giant sandwich” explant. In these explants, cell elongation and wedging are induced in the superficial neural layer by planar signals without persistent vertical interactions with underlying, involuted mesoderm. A neural trough forms, and neural folds form and approach one another. However, the neural folds do not fuse with one another, and the deep cells of these explants do not undergo their normal behaviors of elongation, wedging, and intercalation between the superficial neural cells, even when planar signals are supplemented with vertical signaling until the late midgastrula (stage 11.5). Vertical interactions with mesoderm during and beyond the late gastrula stage were required for expression of these deep cell behaviors and for neural fold fusion. These explants offer a way to regulate deep and superficial cell behaviors and thus make possible the analysis of the relative roles of these behaviors in closing the neural tube
Interspecies Exchange of a Hoxd Enhancer in Vivo Induces Premature Transcription and Anterior Shift of the Sacrum

AbstractThe precise activation, in space and time, of vertebrateHoxgenes is an essential requirement for normal morphogenesis. In order to assess for the functional potential of evolutionary conservedHoxregulatory sequences, a phylogenetically conserved bipartite regulatory element necessary for proper spatial and temporal activation of theHoxd-11gene was replaced by its fish counterpart in theHoxDcomplex of mice, using an ES cell-based targeted exchange. Fetuses carrying this replacement activatedHoxd-11transcription prematurely, which led to a rostral shift of its expression boundary and a consequent anterior transposition of the sacrum. These results demonstrate the high phylogenetic conservation of regulatory mechanisms acting over vertebrateHoxcomplexes and suggest that minor time difference (heterochronies) inHoxgene activation may have contributed to important morphological variations in the course of evolution
Limb Initiation and Development Is Normal in the Absence of the Mesonephros

AbstractWith rapid progress in understanding the genes that control limb development and patterning interest is becoming focused on the factors that permit the emergence of the limb bud. The current hypothesis is that FGF-8 from the mesonephros induces limb initiation. To test this, the inductive interaction between the Wolffian duct and intermediate mesoderm was blocked rostral to the limb field, preventing mesonephric differentiation while maintaining the integrity of the limb field. The experimental outcome was monitored by following expression ofcSim1andLmx1,molecular markers for the duct and the mesonephros, respectively. Evidence is presented that the intermediate mesoderm undergoes apoptosis when the inductive interaction with the Wolffian duct is blocked.fgf-8expression was undetectable in the mesonephric area of embryos with confirmed absence of mesonephros; nevertheless, limb buds formed and limb development was normal. The mesonephros in general, and specifically itsfgf-8expression, was shown to be unnecessary for limb initiation and development; the hypothesis linking the mesonephros and limb development is not supported. Further studies of axial influences on limb initiation should now concentrate on medial structures such as Hensen's node and paraxial mesoderm; the alternative that no axial influences are required should also be examined
Genetic and Functional Analysis of neuronatin in Mice with Maternal or Paternal Duplication of Distal Chr 2

AbstractFunctional differences between parental genomes are due to differential expression of parental alleles of imprinted genes. Neuronatin (Nnat) is a recently identified paternally expressed imprinted gene that is initially expressed in the rhombomeres and pituitary gland and later more widely in the central and peripheral nervous system mainly in postmitotic and differentiating neuroepithelial cells.Nnatmaps to distal chromosome (Chr) 2, which contains an imprinting region that causes morphological abnormalities and early neonatal lethality. More detailed mapping analysis ofNnatshowed that it is located between the T26H and T2Wa translocation breakpoints which is, surprisingly, proximal to the reported imprinting region between the T2Wa and T28H translocation breakpoints, suggesting that there may be two distinct imprinting regions on distal chromosome 2. To investigate the potential role ofNnat,we compared normal embryos with those which were PatDp.dist2.T26H (paternal duplication/maternal deficiency of chromosome 2 distal to the translocation breakpoint T26H) and MatDp.dist2.T26H. Expression ofNnatwas detected in the PatDp.dist2.T26H embryos, where both copies ofNnatare paternally inherited, and normal embryos but no expression was detected in the MatDp.dist2.T26H embryos with the two maternally inherited copies. The differential expression ofNnatwas supported by DNA methylation analysis with the paternally inherited alleles being unmethylated and the maternal alleles fully methylated. Although experimental embryos appeared grossly similar phenotypically in the structures where expression ofNnatwas detected, differences in folding of the cerebellum were observed in neonates, and other more subtle developmental or behavioral effects due to gain or loss ofNnatcannot be ruled out
Intracellular pH Increase Driven by an Na+/H+ Exchanger upon Activation of Surf Clam Oocytes

AbstractIntracellular pH (pHi) measurements were performed in surf clam (Spisula solidissima) oocytes before and after artificial activation or fertilization [evidenced by germinal vesicle breakdown (GVBD)] by the dimethyloxazolidinedione (DMO) and 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) methods. Results using both methods showed increases of pHiof 0.3 pH unit after activation by excess K+. Using BCECF, we found an increase of similar magnitude after fertilization or after the addition of serotonin. By contrast, GVBD did not occur when the pHiwas increased to similar or even higher levels by exposing the oocytes to ammonia. In sodium-free seawater, excess K+induced GVBD but the pHiof K+-activated oocytes decreased significantly below the resting level of unactivated oocytes. The pHiincreases in K+-activated oocytes were otherwise proportional to the external Na+concentration. The amiloride derivatives dimethylamiloride and hexamethylene amiloride (at 10–50 μM) efficiently inhibited the K+-induced increase of pHibut did not block GVBD. These two derivatives were able, however, to retard K+-induced GVBD, hexamethylene amiloride being the more efficient. This retardation of K+-induced GVBD could be abolished by the simultaneous addition of ammonia. Taken altogether, these results show that a pHiincrease, driven by a typical Na+/H+exchanger, follows activation of surf clam oocytes but that this pHiincrease is neither sufficient nor required for GVBD, though it does allow its progression at an optimal rate
Zygotic Transcription Is Required to Block a Maternal Program of Apoptosis inXenopusEmbryos

AbstractAt the midblastula transition duringXenopusdevelopment, the cell cycle is remodeled, and zygotic transcription is initiated. Additionally, cyclin E1 is degraded at the midblastula transition independently of protein synthesis, the number of cell cycles, and the nuclear-to-cytoplasmic ratio. In the studies reported here, cell cycles were delayed by transient inhibition of protein synthesis with cycloheximide (100 μg/ml) prior to the midblastula transition. Even after reaccumulation of mitotic cyclins and resumption of cell divisions, cycloheximide-treated embryos did not resume DNA synthesis, failed to initiate transcription, and synchronously became apoptotic before the gastrula stage. These results were independent of the stage at which embryos were treated or the duration of treatment. Inhibition of zygotic transcription with α-amanitin also induced apoptosis. These data suggest that a developmental checkpoint at the midblastula transition is maternally regulated and can trigger apoptosis. Apoptosis induced by cycloheximide or α-amanitin was blocked by injection of RNA encodingXenopusBcl-2, suggesting that this maternal program is normally blocked by expression of an apoptotic inhibitor. Embryos pulsed with lower doses of cycloheximide (10 μg/ml) delayed development prior to the midblastula transition but resumed DNA synthesis, initiated transcription, and gastrulated normally. This indicates that the apoptotic response is initiated only when delayed embryos are unable to support initiation of zygotic transcription
Mash2 Acts Cell Autonomously in Mouse Spongiotrophoblast Development

AbstractTheMash2gene, which encodes a basic helix-loop-helix transcription factor, is one of the mammalian homologues of theDrosophila achaete-scutegenes. It is strongly expressed in diploid trophoblast cells of the postimplantation mouse embryo. Targeted mutagenesis ofMash2revealed that loss of function results in embryonic lethality at midgestation, due to placental failure associated with a lack of spongiotrophoblast and reduced labyrinthine trophoblast layers. For the further study of Mash2 function in development of the trophoblast cell lineage, we have performed chimeric analysis combiningMash2mutant and wild-type embryos. We have addressed the question of whether the phenotype of theMash2mutant embryo, which affects all of the three trophoblast cell layers, is caused by a cell autonomous or non-autonomous defect and whether Mash2 is required in both spongiotrophoblast and labyrinthine trophoblast development. Our results showed no contribution ofMash2mutant cells to the spongiotrophoblast layer in chimeric placentae at 10.5 and 12.5 days postcoitum, suggesting that the product of theMash2gene is required cell autonomously during the development of the spongiotrophoblast. However, it seems that Mash2 is not required for development of labyrinthine trophoblast or giant cells, since high contributions ofMash2mutant cells were observed in those trophoblast cell layers in the chimeric placentae analyzed. We can therefore conclude that the primary and cell-autonomous function of Mash2 appears to be an involvement in the development of diploid trophoblast cells in the ectoplacental cone to form the spongiotrophoblast cell layer of the mature chorioallantoic placenta
Defects of the Chorioallantoic Placenta in Mouse RXRα Null Fetuses

AbstractThe active derivatives of vitamin A (the retinoids) play important and multiple roles in mammalian development and homeostasis. We have previously shown that specific retinoic acid receptors are expressed in the chorioallantoic placenta of the mouse and that among these, RXRα is strongly expressed in the developing labyrinthine zone (Sapin, V., Ward, S. J., Bronner, S., Chambon, P., Dollé, P.,Dev. Dyn.208, 199–210, 1997). Here, we show that mouse fetuses with a targeted disruption of the RXRα gene develop defects of the chorioallantoic placenta. Both morphological abnormalities and alterations in the expression of molecular markers were found, mostly confined to the labyrinthine zone of placentas from mid–late gestation mutants. This region exhibited edema, abnormal stasis of maternal blood, and signs of disruption of the endothelial layer of fetal vessels. We also detected a reduction in the number of lipid droplets in the trophoblastic layer and abnormal fibrin deposits in the junctional zone of the mutant placentas. These abnormalities most probably result in an impairment of the functional capacities of exchange between the maternal and fetal circulations in the mutant placentas. Thus, placental defects could represent an extraembryonic cause of lethality for RXRα null mutant fetuses, in addition to the previously described embryonic cardiac defects
Origin and Differentiation of Supernumerary Midline Glia inDrosophilaEmbryos Deficient for Apoptosis

AbstractDrosophilaembryos deficient for programmed cell death produce 9 midline glia (MG) in addition to the wild-type complement of 3.2 MG/segment. More than 3 of the supernumerary MG derive from the MGP (MG posterior) lineage and the remainder from the MGA/MGM (MG anterior and middle) lineage. There is one unidentified additional neuron in the mesectoderm of embryos deficient for apoptosis. The supernumerary MG are not diverted from other lineages nor do they arise from an altered pattern of mitosis. Instead, these MG appear to arise from a normally existing pool of 12 precursor cells, larger than anticipated by earlier studies. During normal development, MG survival is dependent upon signaling to theDrosophilaEGF receptor. The persistence of supernumerary MG in embryos deficient for apoptosis does not alter the spatial pattern ofDrosophilaEGF receptor signaling. The number and position of MG which express genes dependent upon EGF receptor function, such aspointedorargos,are indistinguishable from wild type. Genes of the spitz group are required forDrosophilaEGF receptor function. Surviving MG in spitz group/H99double mutants continue to express genes characteristic of the MG, but the cells fail to differentiate into ensheathing glia and are displaced from the nerve cord
Conserved Anterior Boundaries of Hox Gene Expression in the Central Nervous System of the LeechHelobdella

AbstractMolecular developmental studies of fly and mouse embryos have shown that the identity of individual body segments is controlled by a suite of homeobox-containing genes called the Hox cluster. To examine the conservation of this patterning mechanism in other segmented phyla, we here describe four Hox gene homologs isolated from glossiphoniid leeches of the genusHelobdella.Based on sequence similarity and phylogenetic analysis, the leech genesLox7, Lox6, Lox20,andLox5are deemed to be orthologs of theDrosophilageneslab, Dfd, Scr,andAntp,respectively. Sequence similarities betweenLox5andAntpoutside the homeodomain and phylogenetic reconstructions suggest that the Antennapedia family of Hox genes (as defined by Bürglin, 1994) had already expanded to include at least two discreteAntpandUbx/abdAprecursors prior to the annelid/arthropod divergence.In situhybridization reveals that the fourLoxgenes described in this study are all expressed at high levels within the segmented portion of the central nervous system (CNS), with variable levels of expression in the segmental mesoderm. Little or no expression was seen in peripheral ectoderm or endoderm, or in the unsegmented head region (prostomium). EachLoxgene has a distinct anterior expression boundary within one of the four rostral segments, and the anterior-posterior (AP) order of these expression boundaries is identical to that reported for the orthologous Hox gene products in fly and mouse. This finding supports the idea that the process of AP axis differentiation is conserved among the higher metazoan phyla with respect to the regional expression of individual Hox genes along that axis. One unusual feature of leech Hox genes is the observation that some genes are only expressed during later development -- beginning at the time of terminal cell differentiation -- whereas others begin expression at a much earlier stage, and their RNA ceases to be detectable shortly after the onset of expression of the ‘late’ Hox genes. The functional significance of this temporal disparity is unknown, but it is noteworthy that only the two ‘early’ Hox genes display high levels of mesodermal expression
Inhibitory Effects of Ventral Signals on the Development of Brn-3.0-Expressing Neurons in the Dorsal Spinal Cord

AbstractBrn-3.0, a POU-domain transcription factor, is expressed in specific postmitotic neurons in the dorsal part of the neural tube which are among the first spinal cord neurons to appear in development. In the mature spinal cord, the Brn-3.0 cells form a numerous population of scattered neurons in the intermediate spinal gray. Ablation of the notochord in chick embryos extends the domain of Brn-3.0 expression into the ventral neural tube, while ectopic grafts of notochord tissue suppress Brn-3.0 expression. The notochord effects on Brn-3.0 expression are reproducedin vivoby the implantation of a local source of recombinant Shh protein. The down-regulation of Brn-3.0 expression in the dorsal spinal cord by the notochord and Shh contrasts with the known inductive effects of these ventral signals on the approximately simultaneous development of the spinal motor neurons. In cultured explants of neural plate from the region of the presumptive spinal cord, Brn-3.0 neurons develop in the absence of surface ectoderm and ventral midline tissue, suggesting that the Brn-3.0 phenotype may represent a “default” developmental pathway for early spinal cord neurons. Together these results advance the understanding of the mechanism of the generation of neuronal diversity in the developing vertebrate CNS
xnf7 Functions in Dorsal–Ventral Patterning of the Xenopus Embryo

AbstractXenopusnuclear factor 7 (xnf7) is a maternally expressed nuclear protein that is retained in the cytoplasm from oocyte maturation until the midblastula transition (MBT). Mutations of the xnf7 phosphorylation sites to glutamic acids (dnxnf7) resulted in the retention of the endogenous protein in the cytoplasm past the MBT, indicating that cytoplasmic retention is a phosphorylation dependent process. In addition, dnxnf7 acted as a dominant negative mutant by keeping the endogenous xnf7 protein in the cytoplasm past the MBT. Overexpression of dnxnf7 in future dorsal blastomeres resulted in a ventralized or posteriorized phenotype in which the embryos lacked anterior structures, while overexpression in ventral blastomeres resulted in dorsalized embryos. dnxnf7 also affected the expression of both dorsal and ventral mesodermal markers. These data suggest that xnf7 functions in dorsal/ventral patterning and that the movement of the protein from the cytoplasm to the nucleus at the MBT is critical for the execution of a genetic program conferring a dorsal or ventral identity to the mesoderm
The Region Encoded by the Alternatively Spliced Exon IIIA in Mesenchymal Fibronectin Appears Essential for Chondrogenesis at the Level of Cellular Condensation

AbstractFibronectin in the extracellular matrix of tissues acts as a substrate for cell adhesion and migration during development. Heterogeneity in the structure of fibronectin is largely due to the alternative splicing of at least three exons (IIIB, IIIA, and V) during processing of a single primary transcript. Fibronectin mRNA alternative splicing patterns change from B+A+V+ to B+A−V+ during chondrogenesis. In this report, immunohistochemical analysis demonstrates that while fibronectin protein containing the region encoded by exon IIIB is present throughout the limb at all stages of development, fibronectin protein containing the region encoded by exon IIIA disappears from cartilaginous regions just after condensationin vivoand in high-density mesenchymal micromass culturesin vitro.Treatment of mesenchymal micromass cultures prior to condensation with an antibody specific for the region encoded by exon IIIA disrupts the formation of cellular condensations and inhibits subsequent chondrogenesis in a dose- and time-dependent manner. Furthermore, microinjection of the exon IIIA antibody into embryonic chick limb primordiain vivoresults in malformations characterized by smaller limbs and loss of limb skeletal elements. These results strongly suggest that the presence of the region encoded by exon IIIA in mesenchymal fibronectin is necessary for the condensation event that occurs during chondrogenesis
Expression of Betacellulin and Epiregulin Genes in the Mouse Uterus Temporally by the Blastocyst Solely at the Site of Its Apposition Is Coincident with the “Window” of Implantation

AbstractIn the mouse, the process of implantation is initiated by the attachment reaction between the blastocyst trophectoderm and uterine luminal epithelium that occurs at 2200–2300 h on day 4 (day 1 = vaginal plug) of pregnancy. Several members of the EGF family are considered important in embryo–uterine interactions during implantation. This investigation demonstrates that the expression of two additions to the family, betacellulin and epiregulin, are exquisitely restricted to the mouse uterine luminal epithelium and underlying stroma adjacent to the implanting blastocyst. These genes are not expressed during progesterone-maintained delayed implantation, but are rapidly switched on in the uterus surrounding the implanting blastocyst following termination of the delay by estrogen. These results provide evidence that expression of betacellulin and epiregulin in the uterus requires the presence of an active blastocyst and suggest an involvement of these growth factors in the process of implantation
MAP and cdc2 Kinase Activities at Germinal Vesicle Breakdown inChaetopterus

AbstractIn frog oocytes, activation of mitogen-activated protein kinase (MAPK, ERK) leads to activation of cdc2 and germinal vesicle breakdown (GVBD). By contrast, in starfish, MAPK is activated after GVBD. Here we have examined the relative involvements of MAPK and cdc2 in GVBD ofChaetopterusoocytes. MAPK was rapidly tyrosine-phosphorylated and activated (within 1–2 min) in response to exposure of the oocytes either to natural seawater (the normal trigger of GVBD in this organism) or to the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), which can also elicit GVBD. This response preceded the tyrosine dephosphorylation and activation of cdc2 by several minutes. MAPK phosphorylation and activation were transient, lasting only until GVBD occurred and the spindle migrated to the cortex. The enzyme was not phosphorylated again as a result of egg activation. These results are consistent with the hypothesis that the activation of MAPK has a role in GVBD. However, PD 98059, a potent and selective inhibitor of MEK, the protein kinase that phosphorylates and activates MAPK, blocked the phosphorylation of MAPK but did not block GVBD, the dephosphorylation and activation of cdc2, or spindle formation and migration. Oocytes that underwent GVBD in PD 98059 could be fertilized and cleaved normally. Ionophore A23187, although it caused germinal vesicles to disappear and caused transient phosphorylation of MAPK, did not cause dephosphorylation of cdc2, and therefore this disappearance is artifactual. These results suggest that MAPK activation is neither obligatory nor sufficient for either GVBD or meiotic metaphase arrest inChaetopterusand that activation of MAPK and cdc2 occur on independent, parallel pathways