pinecone/core-2020-05-10-deduplication huggingface dataset:
Altered Retinoid Signaling in the Heads of Small eye Mouse Embryos

AbstractThe vitamin A derivative retinoic acid (RA) is necessary for eye development, though its role in signaling within eye tissues is poorly understood. We investigated this question in two transgenic mouse strains carrying a retinoic acid response element (RARE) fused to β-galactosidase that identify regions of the embryo expressing activated retinoic acid receptors. Retinoid signaling appears in the retina and lens ectoderm of wild-type embryos prior to neural tube closure, when lens induction is under way. To determine if there are interactions between retinoid signaling and the transcription factor Pax-6, also essential for lens development, we examined RARE transgene expression in Small eye (Sey) mice, which carry a Pax-6 mutation. Retinoid signaling in the eye, nose, and forebrain of Sey embryos is decreased, with the most severe effects in the developing lens. In Sey mice the lens anlage cannot respond to exogenous RA after E9, though it is responsive earlier; the retina and other neural ectoderm can respond to RA at any stage. In Sey mice the ability of presumptive lens and retina to produce and/or sequester RA is also decreased, as assayed with a retinoid–reporter cell line. These results implicate retinoid signaling in lens formation and show that RA signaling in the developing eye is dependent upon Pax-6
Expression of a Novel Receptor Tyrosine Kinase Gene and a paired-like Homeobox Gene Provides Evidence of Differences in Patterning at the Oral and Aboral Ends of Hydra

AbstractAxial patterning of the aboral end of the hydra body column was examined using expression data from two genes. One, shin guard, is a novel receptor protein-tyrosine kinase gene expressed in the ectoderm of the peduncle, the end of the body column adjacent to the basal disk. The other gene, manacle, is a paired-like homeobox gene expressed in differentiating basal disk ectoderm. During regeneration of the aboral end, expression of manacle precedes that of shin guard. This result is consistent with a requirement for induction of peduncle tissue by basal disk tissue. Our data contrast with data on regeneration of the oral end. During oral end regeneration, markers for tissue of the tentacles, which lie below the extreme oral end (the hypostome), are detected first. Later, markers for the hypostome itself appear at the regenerating tip, with tentacle markers displaced to the region below. Additional evidence that tissue can form basal disk without passing through a stage as peduncle tissue comes from LiCl-induced formation of patches of ectopic basal disk tissue. While manacle is ectopically expressed during formation of basal disk patches, shin guard is not. The genes examined also provide new information on development of the aboral end in buds. Although adult hydra are radially symmetrical, expression of both genes in the bud's aboral end is initially asymmetrical, appearing first on the side of the bud closest to the parent's basal disk. The asymmetry can be explained by differences in positional information in the body column tissue that evaginates to form a bud. As predicted by this hypothesis, grafts reversing the orientation of evaginating body column tissue also reverse the orientation of asymmetrical gene expression
Neural Cell Adhesion Molecule (NCAM) and Myoblast Fusion

AbstractConsiderable evidence points to an involvement of neural cell adhesion molecule (NCAM) in myoblast fusion. Changes in the level of NCAM expression, isoform specificity, and localization in muscle cells and tissues correspond to key morphogenetic events during muscle differentiation and repair. Furthermore, anti-NCAM antibodies have been shown by others to reduce the rate of myoblast fusion, whereas overexpression of NCAM cDNAs increases the rate of myoblast fusion compared to controls. In this study we have used a novel fusion assay based on intracistronic complementation of lacZ, in combination with fluorescent X-gal histochemistry and immunocytochemistry to assess levels of NCAM expression in individual muscle cells. Our results indicate that a substantial proportion of newly fused myoblasts have NCAM expression levels unchanged from the levels of the surrounding unfused population suggesting that increased expression of NCAM is not required for wild-type myoblasts to fuse. Moreover, pure populations of primary myoblasts isolated from mice homozygous null for NCAM and therefore lacking the molecule, when placed in differentiation medium, consistently fused to form contractile myotubes with kinetics equivalent to wild-type primary myoblasts. We conclude that the increase in expression of NCAM, although typically observed during myogenesis, is not essential to myoblast fusion to form myotubes
Functional Analysis of Spermatogonial Stem Cells in Steel and Cryptorchid Infertile Mouse Models

AbstractSpermatogenesis is a complex and productive process that originates from stem cell spermatogonia and ultimately results in formation of mature spermatozoa. The stem cell undergoes self-renewal throughout life, but study of its biological characteristics has been difficult because a very small number (2 to 3 in 104 cells) exist in the testis and they can only be identified by function. Although the development of the spermatogonial transplantation technique has provided an assay system for stem cells, efficient methods to enrich stem cells have not been available. Here, we examined two infertile mouse models, Steel/SteelDickie(Sl/Sld) and experimental cryptorchid, as a source of testis cell populations enriched in stem cells. The Sl/Sld testis showed little enrichment, which raises questions about how adult stem cell number is determined and about the currently accepted belief that adult stem cells are independent of Sl factor. The cells recovered from cryptorchid testes were enriched for stem cells 25-fold (colonies) or 50-fold (area) compared to wild-type testes. The cryptorchid condition does not affect stem cell activity, but eliminates almost all differentiated cells, and about 1 in 200 cells is a stem cell. Thus, cryptorchid testes provide an important approach for purification and characterization of spermatogonial stem cells
Characterization of Polo-like Kinase 1 during Meiotic Maturation of the Mouse Oocyte

AbstractWe have characterized plk1 in mouse oocytes during meiotic maturation and after parthenogenetic activation until entry into the first mitotic division. Plk1 protein expression remains unchanged during maturation. However, two different isoforms can be identified by SDS–PAGE. A fast migrating form, present in the germinal vesicle, seems characteristic of interphase. A slower form appears as early as 30 min before germinal vesicle breakdown (GVBD), is maximal at GVBD, and is maintained throughout meiotic maturation. This form gradually disappears after exit from meiosis. The slow form corresponds to a phosphorylation since it disappears after alkaline phosphatase treatment. Plk1 activation, therefore, takes place before GVBD and MAPK activation since plk1 kinase activity correlates with its slow migrating phosphorylated form. However, plk1 phosphorylation is inhibited after treatment with two specific p34cdc2 inhibitors, roscovitine and butyrolactone, suggesting plk1 involvement in the MPF autoamplification loop. During meiosis plk1 undergoes a cellular redistribution consistent with its putative targets. At the germinal vesicle stage, plk1 is found diffusely distributed in the cytoplasm and enriched in the nucleus and during prometaphase is localized to the spindle poles. At anaphase it relocates to the equatorial plate and is restricted to the postmitotic bridge at telophase. After parthenogenetic activation, plk1 becomes dephosphorylated and its activity drops progressively. Upon entry into the first mitotic M-phase at nuclear envelope breakdown plk1 is phosphorylated and there is an increase in its kinase activity. At the two-cell stage, the fast migrating form with weak kinase activity is present. In this work we show that plk1 is present in mouse oocytes during meiotic maturation and the first mitotic division. The variation of plk1 activity and subcellular localization during this period suggest its implication in the organization and progression of M-phase
Ring Formation Drives Invagination of the Vulva in Caenorhabditis elegans: Ras, Cell Fusion, and Cell Migration Determine Structural Fates

AbstractDirected cell rearrangements occur during gastrulation, neurulation, and organ formation. Despite the identification of developmental processes in which invagination is a critical component of pattern formation, little is known regarding the underlying cellular and molecular details. Caenorhabditis elegans vulval epithelial cells undergo morphological changes that generate an invagination through the formation of seven stacked rings. Here, we study the dynamics of ring formation during multivulva morphogenesis of a let-60/ras gain-of-function mutant as a model system to explore the cellular mechanisms that drive invagination. The behavior of individual cells was analyzed in a let-60/ras mutant by three-dimensional confocal microscopy. We showed that stereotyped cell fusion events occur within the rings that form functional and nonfunctional vulvae in a let-60/ras mutant. Expression of let-60/ras gain-of-function results in abnormal cell migration, ectopic cell fusion, and structural fate transformation. Within each developing vulva the anterior and posterior halves develop autonomously. Contrary to prevailing hypotheses which proposed three cell fates (1°, 2°, and 3°), we found that each of the seven rings is a product of a discrete structural pathway that is derived from arrays of seven distinct cell fates (A, B, C, D, E, F, and H). We have also shown how autonomous ring formation is the morphogenetic force that drives invagination of the vulva
A Sequence-Specific RNA Binding Complex Expressed in Murine Germ Cells Contains MSY2 and MSY4

AbstractThe protamine mRNAs are stored for up to 8 days as translationally repressed ribonucleoprotein particles during murine spermatogenesis. Translational repression of the protamine 1, Prm1, mRNA is controlled by sequences in its 3′-untranslated region (UTR). In this study we used the yeast three-hybrid system to clone Msy4, which encodes a novel member of the Y box family of nucleic acid binding proteins. MSY4 specifically binds to a site within the 5′ most 37 nucleotides in the Prm1 3′ UTR. Msy4 is highly expressed in the testis, and the protein is detected in the cytoplasm of germ cells in both the testis and the ovary, where repressed messages are stored. Analysis of a previously described 48/50-kDa binding activity in testis extracts by electrophoretic mobility shift assays and immunoprecipitation indicates the activity is composed of MSY4 and MSY2, another mouse Y box protein. Polysome analysis demonstrates MSY4 is associated with mRNPs, consistent with MSY4 having a role in storing repressed messages
Engrailed-1 Misexpression in Chick Embryos Prevents Apical Ridge Formation but Preserves Segregation of Dorsal and Ventral Ectodermal Compartments

AbstractUsing lineage tracers, we recently showed dorsal and ventral ectodermal compartments along the sides of the body in chick embryos. The compartments are formed both in presumptive limb-forming regions where they position the apical ridge and also in presumptive interlimb (flank). Here we show, using a novel technique combining fate mapping and in situ hybridisation, that the ventral compartment coincides with the Engrailed-1 (En-1) domain of expression. This coincidence suggests that En-1 could maintain the ventral compartment and be necessary for apical ridge formation. To test this hypothesis, we ectopically expressed En-1 via retroviral transfer and then examined limb development and cell lineage restriction in the ectoderm. En-1 misexpression can completely prevent formation of both normal limbs and ectopic limbs induced in the flank by application of FGF-2. In both cases, there are no morphological signs of apical ectodermal ridge formation and expression of ridge-associated genes is undetectable. In striking contrast, the lineage restriction between dorsal and ventral ectoderm is not altered. Therefore, En-1 is involved in the regulation of ridge formation but not compartment maintenance
Axon Guidance in the Mouse Optic Chiasm: Retinal Neurite Inhibition by Ephrin “A”-Expressing Hypothalamic Cells in Vitro

AbstractIn the mammalian visual system, retinal axons undergo temporal and spatial rearrangements as they project bilaterally to targets on the brain. Retinal axons cross the neuraxis to form the optic chiasm on the hypothalamus in a position defined by overlapping domains of regulatory gene expression. However, the downstream molecules that direct these processes remain largely unknown. Here we use a novel in vitro paradigm to study possible roles of the Eph family of receptor tyrosine kinases in chiasm formation. In vivo, Eph receptors and their ligands distribute in complex patterns in the retina and hypothalamus. In vitro, retinal axons are inhibited by reaggregates of isolated hypothalamic, but not dorsal diencephalic or cerebellar cells. Furthermore, temporal retinal neurites are more inhibited than nasal neurites by hypothalamic cells. Addition of soluble EphA5-Fc to block Eph “A” subclass interactions decreases both the inhibition and the differential response of retinal neurites by hypothalamic reaggregates. These data show that isolated hypothalamic cells elicit specific, position-dependent inhibitory responses from retinal neurites in culture. Moreover, these responses are mediated, in part, by Eph interactions. Together with the in vivo distributions, these data suggest possible roles for Eph family members in directing retinal axon growth and/or reorganization during optic chiasm formation
Role of cAMP-Dependent Protein Kinase during Growth and Early Development of Dictyostelium discoideum

AbstractcAMP-dependent protein kinase (PKA) is an essential regulator of gene expression and cell differentiation during multicellular development of Dictyostelium discoideum. Here we show that PKA activity also regulates gene expression during the growth phase and at the transition from growth to development. Overexpression of PKA leads to overexpression of the discoidinIγ promoter, while expression of the discoidinIγ promoter is reduced when PKA activity is reduced, either by expression of a dominant negative mutant of the regulatory subunit or by disruption of the gene for the catalytic subunit (PKA-C). The discoidin phenotype of PKA-C null cells is cell autonomous. In particular, normal secretion of discoidin-inducing factors was demonstrated. In addition, PKA-C null cells are able to respond to media conditioned by PSF and CMF. We conclude that PKA is a major activator of discoidin expression. However, it is not required for production or transduction of the inducing extracellular signals. Therefore, PKA-dependent and PKA-independent pathways regulate the expression of the discoidin genes
Exogenous FGF-4 Can Suppress Anterior Development in the Mouse Embryo during Neurulation and Early Organogenesis

AbstractMembers of the fibroblast growth factor (FGF) family of peptide growth factors are widely expressed in the germ layer derivatives during gastrulation and early organogenesis of the mouse. We have investigated the effect of administering recombinant FGF-4 in the late-primitive streak stage embryo to test if the patterning of the body plan may be influenced by this growth factor. Shortly after FGF treatment the embryonic tissues up-regulated the expression of Brachyury and the RTK signaling regulator Spry2, suggesting that FGF signaling was activated as an immediate response to exogenous FGF. Concomitantly, Hesx1 expression was suppressed in the prospective anterior region of the embryo. After 24 h of in vitro development, embryos displayed a dosage-related suppression of forebrain morphogenesis, disruption of the midbrain–hindbrain partition, and inhibition of the differentiation of the embryonic mesoderm. Overall, development of the anterior–posterior axis in the late gastrula is sensitive to the delivery of exogenous FGF-4. The early response associated with the expression of Spry2 suggests that the later phenotype observed could be primarily related to an inhibition of the FGF signaling pathway
Evolution of Vulva Development in the Cephalobina (Nematoda)

AbstractVentral cord and vulva development are analyzed in a large sample of nematode species of the suborder Cephalobina. We find a specific range of evolutionary variations at distinct developmental steps. (1) Unlike Caenorhabditis elegans and relatives, the vulva is formed from the four precursor cells P(5–8).p or, exceptionally, from P(6,7).p only. (2) The vulval competence group is restricted to these four cells or is larger. (3) The fates of more anterior and posterior Pn.p cells vary between closely related species (mostly cell death versus epidermal fate). (4) The mechanism of vulval cell fate patterning varies within a single genus, even between strains of the same species. (5) We describe the first example of a vulval cell lineage that is asymmetric between the anterior and the posterior sides of the vulva. For a selection of the investigated taxa, phylogenetic trees were constructed in order to map vulval characters and infer evolutionary polarities. We can conclude that in this group, death of the Pn.p cells probably constitutes a derived character state compared to a syncytial fate. Rhabditophanes sp. and Strongyloides ratti are placed as sister taxa, probably sharing an exclusive common ancestor in which the number of precursor cells forming the vulva was reduced from four to two
More Than 95% Reversal of Left–Right Axis Induced by Right-Sided Hypodermic Microinjection of Activin into Xenopus Neurula Embryos

AbstractIn recent years, genes that show left–right (L-R) asymmetric expression patterns have been identified one after another in vertebrate gastrula–neurula embryos. However, we still have little information about when the irreversible L-R specification is established in vertebrate embryos. In this report, we show that almost 100% of the embryos develop to be L-R-inverted larvae after microinjection of activin molecules into the right lateral hypodermic space of Xenopus neurula embryos. After right-side injection of 10–250 pg activin protein, both early neurulae just after gastrulation movement (stage 13–14) and late neurulae just before neural tube closure (stage 17–18) showed almost 100% reversal of the heart and gut L-R axes. At higher doses of activin, more than 90% of the L-R-inverted embryos showed L-R reversal of both heart and gut. The survival ratio of the right-injected 4-day embryos was 90% on average. In the left-injected embryos, the occurrence of L-R inversion was less than 2% as observed in normal untreated siblings (1.7%). When the same amount of activin (1–50 pg) was microinjected into both sides of neurula embryos, the incidence of L-R inversion was reduced to 58%. The injection of activin along the dorsal midline in the trunk region also randomized the visceral L-R axis. Injection of activin into the right side changed normal left-handed expression of Xnr-1 to right-handed or bilateral expression. In contrast, left-handed expression of Pitx2 was switched to the right side by right activin injection. This is the first report of a method that achieves complete inversion of the visceral L-R axis by treatment of embryos at the neurula stage. Activin not only acts on the neurulae to cancel the original L-R specification up to the late neurula stage, but also rebuilds a new L-R axis whose left side coincides with the injection side. It is suggested that the left and right halves of neurulae have equal potential for L-R differentiation
Regeneration in Vertebrates

AbstractOne way or another, all species possess the ability to regenerate damaged tissues. The degree of regeneration, however, varies considerably among tissues within a body and among species, with urodeles being the most spectacular. Such differences in regenerative capacity are indicative of specific mechanisms that control the different types of regeneration. In this review the different types of regeneration in vertebrates and their basic characteristics are presented. The major cellular events, such as dedifferentiation and transdifferentiation, which allow complex organ and body part regeneration, are discussed and common molecular mechanisms are pinpointed
Induction of Early Transcription in One-Cell Mouse Embryos by Microinjection of the Nonhistone Chromosomal Protein HMG-I

AbstractIn the mouse embryo, the onset of zygotic transcription occurs at the end of the first cell cycle, upon completion of DNA replication. We show that the nonhistone chromosomal protein HMG-I, whose translocation into the pronuclei of one-cell embryos is linked to this first round of DNA synthesis, plays a critical role in the activation of zygotic transcription. Indeed, microinjection of purified HMG-I results in a higher nuclear accumulation of the protein and triggers an earlier activation of zygotic transcription, an effect which is abolished by the preincubation of the protein with a specific antibody directed against its AT-hook DNA-binding motifs. Significantly, microinjection of this antibody also prevents the normal onset of transcription in the embryo, suggesting that endogenous HMG-I is similarly involved in this process. Finally, microinjection of the exogenous protein modifies chromatin structure as measured by in situ accessibility to DNase I. We propose that general chromosomal architectural factors such as HMG-I can modulate the accessibility of chromatin to specialized regulatory factors, thereby promoting a transcriptionally competent state
The Control of Cyclin B1 mRNA Translation during Mouse Oocyte Maturation

AbstractIn maturing mouse oocytes, protein synthesis is required for meiotic maturation subsequent to germinal vesicle breakdown (GVBD). While the number of different proteins that must be synthesized for this progression to occur is unknown, at least one of them appears to be cyclin B1, the regulatory subunit of M-phase-promoting factor. Here, we investigate the mechanism of cyclin B1 mRNA translational control during mouse oocyte maturation. We show that the U-rich cytoplasmic polyadenylation element (CPE), a cis element in the 3′ UTR of cyclin B1 mRNA, mediates translational repression in GV-stage oocytes. The CPE is also necessary for cytoplasmic polyadenylation, which stimulates translation during oocyte maturation. The injection of oocytes with a cyclin B1 antisense RNA, which probably precludes the binding of a factor to the CPE, delays cytoplasmic polyadenylation as well as the transition from GVBD to metaphase II. CPEB, which interacts with the cyclin B1 CPE and is present throughout meiotic maturation, becomes phosphorylated at metaphase I. These data indicate that CPEB is involved in both the repression and the stimulation of cyclin B1 mRNA and suggest that the phosphorylation of this protein could be involved in regulating its activity