pinecone/core-2020-05-10-deduplication huggingface dataset:
Mutual Regulation ofdecapentaplegicandhedgehogduring the Initiation of Differentiation in theDrosophilaRetina

AbstractNeuronal differentiation in theDrosophilaretinal primordium, the eye imaginal disc, begins at the posterior tip of the disc and progresses anteriorly as a wave. The morphogenetic furrow (MF) marks the boundary between undifferentiated anterior cells and differentiating posterior cells. Anterior progression of differentiation is driven by Hedgehog, synthesized by cells located posterior to the MF. We report here thathedgehog(hh), which is expressed prior to the start of differentiation along the disc's posterior margin, also plays a crucial role in the initiation of differentiation. Using a temperature-sensitive allele we show thathhis normally required at the posterior margin to maintain the expression ofdecapentaplegic(dpp) and of the proneural geneatonal.In addition, we find that ectopic differentiation driven by ectopicdppexpression or loss ofwinglessfunction requireshh.Consistent with this is our observation that ectopicdppinduces the expression ofhhalong the anterior margin even in the absence of differentiation. Taken together, these data reveal a novel positive regulatory loop betweendppandhhthat is essential for the initiation of differentiation in the eye disc
Mammalian BarH Homologue Is a Potential Regulator of Neural bHLH Genes

AbstractVertebrate neurogenesis involves sequential actions of transcription factors.neurogenins,encoding Atonal-related bHLH transcription factors, function as neuronal determination genes inXenopus. neurogeninsand another bHLH factor gene,Mash1,are expressed in distinct subsets or areas of cells giving rise to neurons, suggesting that these genes play important roles to generate distinct populations of neurons. A mammalian homologue ofBarH(MBH1) is expressed in a complementary pattern toMash1expression in the developing nervous system likeneurogenins.Forced expression ofMBH1down-regulates expression ofMash1and up-regulatesneurogenin2/Math4A,a member ofneurogenins,in P19 cells during neuronal differentiation. This suggests thatMBH1is a potential regulator of mammalian neural bHLH genes, thereby establishing distinct pathways of neuronal differentiation
Roles of Secretion and the Cytoskeleton in Cell Adhesion and Polarity Establishment inPelvetia compressaZygotes

AbstractDuring the establishment of polarity, fucoid algal zygotes adhere to the substratum and select a growth axis according to environmental cues. Since little is known about the early events leading to axis selection, we investigated the chronology of cell adhesion, adhesive deposition, and axis selection induced by light (photopolarization). The requirements for secretion and the cytoskeleton in these processes and in the process of changing the orientation of an axis in response to new environmental cues (axis realignment) were also tested. Adhesive deposition occurred in two distinct stages: it was deposited uniformly on young zygotes (uniform primary adhesive) and later was deposited asymmetrically (polar secondary adhesive). Uniform primary adhesive deposition, cell adhesion, and photopolarization occurred simultaneously, and shortly thereafter, polar secondary adhesive deposition occurred at the future growth site. Uniform primary adhesive deposition and cell adhesion required secretion, but were independent of filamentous-actin (F-actin) and microtubule function. Photopolarization of young zygotes and polar secondary adhesive deposition required secretion but not microtubules. F-actin served to localize secondary adhesive deposition at the rhizoid pole; its function in polarization was more complex. F-actin was required for axis selection; however, its role in realignment of an axis depended on the light regime. The differing requirements for F-actin during development indicates that the axis is not static, but changes with time. These findings indicate that previous and future work on “axis formation” must be interpreted in the context of the developmental stage of the zygote
Alteration in Connexin 43 Gap Junction Gene Dosage Impairs Conotruncal Heart Development

AbstractConnexin 43 (Cx43) knockout mice and transgenic mice (CMV43) overexpressing the Cx43 gap junction gene exhibit heart defects involving the conotruncus and right ventricle. Based on the heart phenotype and Cx43 gene and transgene expression pattern, we previously proposed that the heart defects may reflect a role for gap junctions in the modulation of cardiac neural crest development. To further elucidate the mechanism by which these heart defects may arise, fetal heart structure and function in these transgenic and knockout mice were examined by magnetic resonance microscopy and Doppler echocardiography. Magnetic resonance microscopy of E14.5 fetuses revealed an enlargement of the right ventricular chamber in the heterozygous Cx43 knockout and CMV43 transgenic mice. This was accompanied by thinning of the chamber wall. In the homozygous Cx43 knockout mouse, heart malformation was also restricted to the right ventricle. This was generally characterized by two pouches at the base of the pulmonary outflow tract, but occasionally hearts with a single pouch were found. Magnetic resonance microscopy showed in some of the CMV43 and Cx43 knockout mice an attenuation of the ductus arteriosus, a phenotype which may be indicative of outflow tract obstruction. This was confirmed by thein uteroDoppler echocardiography, which showed increased outflow velocity in E12.5 to 14.5 CMV43 and Cx43 knockout fetuses. In some of these fetuses, Doppler analysis also revealed arrhythmia and absence of isovolemic contraction time. Further examination of these hearts by histology and immunohistochemistry showed abnormal myocardial development in the conotruncus. Particularly interesting was the presence of abundant subendocardial fibrous tissue expressing smooth muscle actin. In the developing heart, such mesenchyme in the outflow tract is usually considered neural crest-derived tissue. Together, these results confirm the importance of Cx43 gene dosage in conotruncal heart development and suggest that this likely involves a role for Cx43 gap junctions in cardiac crest development. In future studies, these transgenic mice may serve as valuable animal models for further studying the role of gap junctions and cardiac crest cells in conotruncal heart development
Evidence That GqFamily G Proteins Do Not Function in Mouse Egg Activation at Fertilization

AbstractEmbryonic development is initiated after the fertilizing sperm contacts the egg and triggers a process termed “egg activation,” resulting in calcium release, cortical granule exocytosis, recruitment of maternal mRNAs, and cell cycle resumption. Heterotrimeric guanine nucleotide-binding proteins (G proteins) may be involved in mouse egg activation since inhibition of G protein βγ subunits partially inhibits sperm-induced cell cycle resumption. In addition, specific events of egg activation can be initiated in the absence of sperm by acetylcholine stimulation of mouse eggs overexpressing the human m1 muscarinic receptor, a G protein-coupled receptor. In somatic cells, G proteins in the Gqfamily couple ligand stimulation of the m1 muscarinic receptor to activation of phospholipase C, resulting in the production of inositol 1,4,5-trisphosphate (IP3) and IP3-mediated release of intracellular calcium. Since IP3-mediated calcium release is involved in egg activation at fertilization, we have examined the role of Gqfamily G proteins in both sperm-independent (muscarinic receptor-mediated) and sperm-induced egg activation using a function-blocking antibody raised against the common C-terminal region of Gqand G11proteins. We show that this antibody effectively inhibits Gqfamily G proteins in mouse eggs by demonstrating that the antibody inhibits egg activation in response to stimulation of the m1 muscarinic receptor. This same antibody, however, does not inhibit sperm-induced egg activation events. These results indicate that although activation of Gqfamily G proteins can result in egg activation in the mouse, it is unlikely that these proteins are used by the sperm to initiate egg activation at fertilization
Xenopus Smad7 Inhibits both the Activin and BMP Pathways and Acts as a Neural Inducer

AbstractSmads are proteins that transduce signals on behalf of members of the TGFβ superfamily of growth factors. Recently, inhibitory Smads, Smad6, Smad7, and Dad, were isolated from human, mouse, and fly. These anti-Smads were shown to inhibit TGFβ signaling by stably associating to TGFβ type I receptors or, as it was shown for Smad6, by binding to receptor-activated Smad1. We report the cloning, distribution, and embryological activity of the Xenopus Smad7 (XSmad7). We report that XSmad7 inhibits signaling from the activin and BMP pathways in animal explants although at different thresholds. When expressed in the embryo, low concentrations of XSmad7 dorsalize the ventral mesoderm, thus inducing a secondary axis. At higher concentrations however, XSmad7 inhibits both mesoderm induction and primary axis specification. In addition, we show that XSmad7 acts as a direct neural inducer both in the context of ectodermal explants andin vivo.We discuss the implications of these findings in the biochemical context of the activin and BMP pathways as well as their implications in mesodermal, neural, and axis specification
Somitogenesis Controlled by Noggin

AbstractIn vertebrates, the segmented somites, which are the medial-most component in the paraxial mesoderm, are the entity giving rise to the axial bones and skeletal muscles. We previously demonstrated that the mechanism that distinguishes the somite from the more lateral mesoderm (lateral plate) involves different levels of BMP-4 activity which is highest in the lateral plate. We report that Noggin, an antagonist of BMP-4, is expressed in the presumptive somite and appears to control effective levels of BMP-4 to differentiate somitic mesoderm from the lateral plate. When Noggin-producing cells were implanted into the presumptive lateral plate, they produced ectopic somites that were respecified from the lateral plate precursors. These somites exhibited no mediolateral (M–L) polarity, but acquired it when implanted Noggin was eliminated. Thus, in normal embryogenesis no or low BMP-4 activity realized by Noggin specifies the somites in the medial-most portion of the paraxial mesoderm, and then BMP-4 emanating from the lateral plate subsequently establishes the M–L polarity in the somites
Maternally Expressed γTub37CD inDrosophilaIs Differentially Required for Female Meiosis and Embryonic Mitosis

AbstractWe report functional analysis of γTub37CD, a maternally synthesized γ-tubulin that is highly expressed during oogenesis and utilized at centrosomes in precellular embryos. TwoγTub37CDmutants contained missense mutations that altered residues conserved in all γ-tubulins and α- and/or β-tubulins. A thirdγTub37CDmissense mutant identified a conserved motif unique to γ-tubulins. A fourthγTub37CDmutant contained a nonsense mutation and the corresponding premature stop codon generated a protein null allele. Immunofluorescence analysis of laid eggs and activated oocytes derived from the mutants revealed microtubules and meiotic spindles that were close to normal even in the absence of γTub37CD. Eggs lacking the maternal γ-tubulin were arrested in meiosis, indicative of a deficiency in activation. Analysis of meiosis within vitroactivation techniques showed that the cortical microtubule cytoskeleton of mature wild-type eggs was reorganized upon activation and expressed as transient assembly of cortical asters, and this cortical reorganization was altered inγTub37CDmutants. In precellular embryos of partial loss of function mutants, spindles were frequently abnormal and cell cycle progression was inhibited. Thus, γTub37CD functions differentially in female meiosis and in the early embryo; while involved in oocyte activation, it is apparently not required or plays a subtle role in formation of the female meiotic spindle which is acentriolar, but is essential for assembly of a discrete bipolar mitotic spindle which is directed by centrosomes organized about centrioles
Neural Induction in Whole Chick Embryo Cultures by FGF

AbstractFGFs are well known as mesodermal inducers and they have been reported to have neural inducing and/or caudalizing activity inXenopus.To evaluate the role of FGFs in neural induction and patterning of the nervous system in chick embryos, we have targeted the ectopic expression of these factors by applying FGF-soaked beads to extended primitive streak chick embryos developing in culture. The whole embryo culture system allows to directly assessing the neural inducing activity on nonneural ectodermal cells. Our results show that FGFs induce the production of ectopic neural structures in the epiblast cell layer which are independent of the endogenous neural tube. The induced neural plates express several neural positional markers (Otx-2, Krox-20, EphA4, EphA7,andcHox-B9), although they lack anterior neural markers such asBF-1.These effects are very likely to be exerted by the direct action of FGF on epiblast cells because we have found no evidence of the induction of an organizer-like activity or of the presence of new axial mesoderm induced by the growth factor. We conclude that FGFs can act as direct neural inducers and that this action is exerted independently from the axial mesoderm
A Constitutive Mutation ofALK5Disrupts Cardiac Looping and Morphogenesis in Mice

AbstractTGFβ family members are implicated in cardiac organogenesis, growth control, and positional information, including the direction of cardiac looping. However, genetic analysis of TGFβ signaling in mice has been confounded, in some cases, by noncardiac and generalized defects. Hence, deciphering TGFβ function in myocardium would benefit from cardiac-restricted mutations. We developed a constitutively activated type I receptor, ALK5L193A,P194A,T204D, and directed it to embryonic myocardium in transgenic mice. Expression of the activatedALK5gene arrests looping morphogenesis and causes a linear, dilated, hypoplastic heart tube, despite normal expression of Nkx2.5 and dHAND, cardiogenic transcription factors whose absence provokes a similar phenotype. Ventricular hypoplasia was associated with precocious induction of the cyclin-dependent kinase inhibitor, p21. Thus, an ALK5-sensitive pathway mediates looping, perhaps through control of cardiac myocyte proliferation
Abdominal B(AbdB)HoxaGenes: Regulation in Adult Uterus by Estrogen and Progesterone and Repression in Müllerian Duct by the Synthetic Estrogen Diethylstilbestrol (DES)

AbstractMice deficient for theAbdominal B (AbdB) HoxgeneHoxa-10exhibit reduced fertility due to defects in implantation. During the peri-implantation periodHoxa-10is sequentially expressed in the uterine epithelium and stroma. These observations, combined with the stringent regulation of uterine implantation by ovarian steroids, prompted us to test whether estrogen and progesterone directly regulate the expression ofHoxa-10and otherAbdB Hoxagenes. Here we show thatHoxa-10expression in the adult uterus is strongly activated by progesterone. This activation is blocked by the progesterone receptor antagonist RU486 and is independent of new protein synthesis. In addition,Hoxa-10expression is repressed by estrogen in a protein synthesis-independent manner. Analysis of adjacentAbdB Hoxagenes reveals thatHoxa-9anda-11are also activated in a colinear fashion by progesterone but differentially regulated by estrogen. These results suggest that the regulation ofAbdB Hoxgene expression in the adult uterus by ovarian steroids is a property related to position within the cluster, mediated by the direct action of estrogen and progesterone receptors upon these genes. We next examined whether the embryonic expression ofHoxa10is regulable by hormonal factors. Previous work has demonstrated that perinatal administration of the synthetic estrogen diethylstilbestrol (DES) to mice and humans produces uterine, cervical, and oviductal malformations. Certain of these phenotypes resemble those inHoxa-10knockout mice, suggesting thatHoxa-10gene expression might be repressed by DES during reproductive tract morphogenesis. Exposure of the developing female reproductive tract to DES, eitherin vivoor in organ culture, represses the expression ofHoxa-10in the Müllerian duct. Thus, these data not only establish a direct link between ovarian steroids andAbdB Hoxagene expression in the adult uterus, but also provide a potential mechanism for the teratogenic effects of DES on the developing reproductive tract
Dynamic Patterns of Retinoic Acid Synthesis and Response in the Developing Mammalian Heart

AbstractRetinoic acid (RA) has been implicated in cardiac morphogenesis by its teratogenic effects on the heart, although its role in normal cardiogenesis remains unknown. To define the parameters of RA action in cardiac morphogenesis, we analyzed the patterns of ligand synthesis, response, and inactivation in the developing mouse heart. Activation of a lacZ transgene controlled by an RA response element (RARE) was compared to the localization of the retinaldehyde-oxidizing dehydrogenase RALDH2, the earliest RA synthetic enzyme in the mouse embryo, and to the expression of a gene encoding an RA-degrading enzyme (P450RA). We observed that RALDH2 localization and RA response were virtually superimposable throughout heart development. Initially, both RALDH2 and RARE-LacZ activity were restricted to the sinus venosa in unlooped hearts, but were high in the dorsal mesocardium, while P450RA expression was restricted to the endocardium. Later stages were characterized by a sequential, noncontiguous progression of RALDH2 accumulation and RA response, from the sinus venosa to atria, dorsal–medial conotruncus, aortic arches, and the epicardium. This dynamic pattern of RA response was a direct result of localized RALDH2, since hearts of cultured embryos were uniformly competent to respond to an exogenous RA challenge. These observations support a model in which the influence of endogenous RA on heart development depends upon localized presentation of the ligand, with only limited diffusion from the source of its synthesis
Progenitor Dispersal and the Origin of Early Neuronal Phenotypes in the Chick Embryo Spinal Cord

AbstractUsing DiI and fluorescent dextrans, we have created fate maps of the neural plate and early neural tube describing the extent of progenitor cell dispersal and the spatial origin of morphologically distinct neuronal cell types along the dorsoventral axis of the developing chick spinal cord. Nonuniform dispersal and mixing of progenitors occur within the early neuroepithelium, with the degree of dispersal being determined by the initial position of the cells along the mediolateral axis of the neural plate. Dispersal is greatest in the midregions of the ventricular epithelium and decreases toward the dorsal and ventral midlines. Phenotypically diverse classes of neurons are born at specific dorsoventral locations in the neural tube. Motor neurons are the most ventral cell type generated followed, at progressively more dorsal positions, by distinct classes of interneurons. Several genes show dorsoventrally restricted patterns of expression within the neural tube and the fate maps were used to investigate the relationship between one of these genes,Pax3,and progenitor cell dispersal and fate. The results indicate that the dorsoventral pattern ofPax3expression is not maintained by restrictions to cell mixing and are consistent with a role for this transcription factor in specifying the identity of neurons with contralateral descending axons
A Common Neural Progenitor for the CNS and PNS

AbstractCultured spinal cord neuroepithelial (NEP) cells can differentiate into neurons, oligodendrocytes and astrocytes and are morphologically and antigenically distinct from neural crest stem cells (NCSCs) that generate the PNS. NEP cells, however, can generate p75/nestin-immunoreactive cells that are morphologically and antigenically similar to previously characterized NCSCs. NEP-derived p75-immunoreactive cells differentiate into peripheral neurons, smooth muscle, and Schwann cells in mass and clonal culture. Clonal analysis of NEP cells demonstrates that a common NEP progenitor cell generated both CNS and PNS phenotypes. Differentiation into NCSCs was promoted by BMP-2/4 and differentiation did not require cells to divide, indicating that BMP played an instructive role in the differentiation process. Thus, individual NEP cells are multipotent and can differentiate into most major types of cell in the CNS and PNS and that PNS differentiation involves a transition from a NEP stem to another more limited, p75-immunoreactive, neural crest stem cell
The Transition to Endoreduplication in Trophoblast Giant Cells Is Regulated by the mSNA Zinc Finger Transcription Factor

AbstractTerminal cell differentiation is usually associated with cell cycle exit. In some lineages, however, cells undergo continued rounds of DNA synthesis without intervening mitoses (endoreduplication) resulting in polyploid nuclei. This is striking in rodent trophoblast giant cells which contain up to 1000N of DNA. InDrosophila,theEscargotgene has been implicated in regulating the transition from mitotic cell cycles to endocycles during development. We found that a murine homologue,mSna,was expressed in mouse trophoblast and was downregulated during giant cell differentiation. The mSNA zinc finger protein bound to E-box DNA elements and, in transfected C3H10T1/2 fibroblasts, acted as a transcriptional repressor. The maximal repressive effect was dependent on both the zinc finger DNA-binding domain and the N-terminal, seven-amino-acid SNAG domain. Misexpression experiments in Rcho-1 trophoblast cells revealed thatmSnaregulates the transition from replicating precursor cells to committed giant cells: overexpression blocked, whereas antisense RNA-mediated underexpression promoted trophoblast giant cell differentiation. Overexpression ofmSnain precursor cells had no effect on cell cycle kinetics, but did increase cyclin A and B levels, implying actions during G2. These effects were dependent on both the zinc finger and SNAG domains. Together, these data suggest that mSNA has an ESCARGOT-like function to repress the transcription of genes that promote the transition from mitotic to endoreduplicative cell cycles in rodent trophoblast
TheTollPathway Is Required in the Epidermis for Muscle Development in theDrosophilaEmbryo

AbstractTheTollsignaling pathway functions in severalDrosophilaprocesses, including dorsal–ventral pattern formation and the immune response. Here, we demonstrate that this pathway is required in the epidermis for proper muscle development. Previously, we showed that the zygotic Toll protein is necessary for normal muscle development; in the absence of zygotic Toll, close to 50% of hemisegments have muscle patterning defects consisting of missing, duplicated and misinserted muscle fibers (Halfon, M.S., Hashimoto, C., and Keshishian, H.,Dev. Biol.169, 151–167, 1995). We have now also analyzed the requirements foreaster, spätzle, tube,andpelle,all of which function in theToll-mediated dorsal–ventral patterning pathway. We find thatspätzle, tube,andpelle,but noteaster,are necessary for muscle development. Mutations in these genes give a phenotype identical to that seen inTollmutants, suggesting that elements of the same pathway used forTollsignaling in dorsal–ventral development are used during muscle development. By expressing theTollcDNA under the control of distinctTollenhancer elements inTollmutant flies, we have examined the spatial requirements for Toll expression during muscle development. Expression of Toll in a subset of epidermal cells that includes the epidermal muscle attachment cells, but not Toll expression in the musculature, is necessary for proper muscle development. Our results suggest that signals received by the epidermis early during muscle development are an important part of the muscle patterning process