pinecone/core-2020-05-10-deduplication huggingface dataset:
Rib Truncations and Fusions in the Sp2HMouse Reveal a Role for Pax3 in Specification of the Ventro-lateral and Posterior Parts of the Somite

AbstractThesplotch (Pax3)mouse mutant serves as a model for developmental defects of several types, including defective migration of dermomyotomal cells to form the limb musculature. Here, we describe abnormalities of the ribs, neural arches, and acromion inSp2Hhomozygous embryos, indicating a widespread dependence of lateral somite development onPax3function. Moreover, the intercostal and body wall muscles, derivatives of the ventrolateral myotome, are also abnormal inSp2Hhomozygotes.Pax3is expressed in the dermomyotome, but not in either the sclerotome or the myotome, raising the possibility thatPax3-dependent inductive influences from the dermomyotome are necessary for early specification of lateral sclerotome and myotome. Support for this idea comes from analysis of gene expression markers of lateral sclerotome (tenascin-Candscleraxis) and myotome (myogenin, MyoD,andMyf5). All exhibit ventrally truncated domains of expression inSp2Hhomozygotes, potentially accounting for the rib and intercostal muscle truncations. In contrast, the medial sclerotomal markerPax1is expressed normally in mutant embryos, arguing thatPax3is not required for development of the medial sclerotome. Most of the somitic markers show ectopic expression in anteroposterior and mediolateral dimensions, suggesting a loss of definition of somite boundaries insplotchand explaining the rib and muscle fusions. An exception isMyf5,which is not ectopically expressed inSp2Hhomozygotes, consistent with the previous suggestion thatPax3andMyf5function in different pathways of skeletal myogenesis. PDGFα and its receptor are candidates for mediating signalling between myotome and sclerotome. We find that both genes are misexpressed inSp2Hembryos, suggesting that PDGFα/PDGFRα may function downstream ofPax3,accounting for the close similarities between thesplotchandPatchmutant phenotypes. Our findings point to additional regulatory functions for the Pax3 transcription factor, apart from those already demonstrated for development of the neural tube, neural crest, and dermomyotome
Thalamocortical Axons Are Influenced by Chemorepellent and Chemoattractant Activities Localized to Decision Points along Their Path

AbstractThalamocortical axons (TCAs), which originate in dorsal thalamus, project ventrally in diencephalon and then dorsolaterally in ventral telencephalon to their target, the neocortex. To elucidate potentially key decision points in TCA pathfinding and hence the possible localization of guidance cues, we used DiI-tracing to describe the initial trajectory of TCAs in mice. DiI-labeled TCAs extend ventrally on the lateral surface of ventral thalamus. Rather than continuing this trajectory onto the lateral surface of the hypothalamus, TCAs make a sharp lateral turn into ventral telencephalon. This behavior suggests that the hypothalamus is repulsive and the ventral telencephalon attractive for TCAs. In support of this hypothesis, we find that axon outgrowth from explants of dorsal thalamus is biased away from hypothalamus and toward ventral telencephalon when cocultured at a distance in collagen gels. Thein vivoDiI analysis also reveals a broad cluster of retrogradely labeled neurons in the medial part of ventral telencephalon positioned within or adjacent to the thalamocortical pathway prior to or at the time TCAs are extending through it. The axons of these neurons extend into or through dorsal thalamus and appear to be coincident with the oppositely extending TCAs. These findings suggest that multiple cues guide TCAs along their pathway from dorsal thalamus to neocortex: TCAs may fasciculate on the axons of ventral telencephalic neurons as they extend through ventral thalamus and the medial part of ventral telencephalon, and chemorepellent and chemoattractant activities expressed by hypothalamus and ventral telencephalon, respectively, may cooperate to promote the turning of TCAs away from hypothalamus and into ventral telencephalon
Dynein–Dynactin Function and Sensory Axon Growth duringDrosophilaMetamorphosis: A Role for Retrograde Motors

AbstractMutations in the genes for components of the dynein–dynactin complex disrupt axon path finding and synaptogenesis during metamorphosis in theDrosophilacentral nervous system. In order to better understand the functions of this retrograde motor in nervous system assembly, we analyzed the path finding and arborization of sensory axons during metamorphosis in wild-type and mutant backgrounds. In wild-type specimens the sensory axons first reach the CNS 6–12 h after puparium formation and elaborate their terminal arborizations over the next 48 h. InGlued1andCytoplasmic dynein light chainmutants, proprioceptive and tactile axons arrive at the CNS on time but exhibit defects in terminal arborizations that increase in severity up to 48 h after puparium formation. The results show that axon growth occurs on schedule in these mutants but the final process of terminal branching, synaptogenesis, and stabilization of these sensory axons requires the dynein–dynactin complex. Since this complex functions as a retrograde motor, we suggest that a retrograde signal needs to be transported to the nucleus for the proper termination of some sensory neurons
Evolutionary Conservation of MyoD Function and Differential Utilization of E Proteins

AbstractThe formation of striated muscle in both vertebrates and invertebrates involves the activity of the MyoD family of basic-helix-loop-helix (bHLH) transcription factors. The high degree of evolutionary conservation of MyoD-related proteins, both in the sequence of their bHLH domains and in their general developmental expression patterns, suggests that these factors are also conserved at the level of function. We have addressed this directly using MyoD and E protein factors from vertebrates,Drosophila,andCaenorhabditis elegans.Various MyoD and E factor combinations were tested for their ability to interactin vitroand to functionin vivoin the myogenic conversion of 10T12mouse fibroblasts. We found that the ability of different homo- and heterodimers to bind DNAin vitrowas an accurate measure of biological activityin vivo.A second assessment of conserved function comes from the ability of these factors to rescue aC. elegans hlh-1(CeMyoD) null mutation. We found that bothDrosophilaand chicken MyoD-related factors were able to rescue aC. elegansCeMyoD loss-of-function mutation. These results demonstrate a remarkable degree of functional conservation of these myogenic factors despite differences in E-protein interactions
Connexin 43 Expression Reflects Neural Crest Patterns during Cardiovascular Development

AbstractWe used transgenic mice in which the promoter sequence for connexin 43 linked to a lacZ reporter was expressed in neural crest but not myocardial cells to document the pattern of cardiac neural crest cells in the caudal pharyngeal arches and cardiac outflow tract. Expression of lacZ was strikingly similar to that of cardiac neural crest cells in quail–chick chimeras. By using this transgenic mouse line to compare cardiac neural crest involvement in cardiac outflow septation and aortic arch artery development in mouse and chick, we were able to note differences and similarities in their cardiovascular development. Similar to neural crest cells in the chick, lacZ-positive cells formed a sheath around the persisting aortic arch arteries, comprised the aorticopulmonary septation complex, were located at the site of final fusion of the conal cushions, and populated the cardiac ganglia. In quail–chick chimeras generated for this study, neural crest cells entered the outflow tract by two pathways, submyocardially and subendocardially. In the mouse only the subendocardial population of lacZ-positive cells could be seen as the cells entered the outflow tract. In addition lacZ-positive cells completely surrounded the aortic sac prior to septation, while in the chick, neural crest cells were scattered around the aortic sac with the bulk of cells distributed in the bridging portion of the aorticopulmonary septation complex. In the chick, submyocardial populations of neural crest cells assembled on opposite sides of the aortic sac and entered the conotruncal ridges. Even though the aortic sac in the mouse was initially surrounded by lacZ-positive cells, the two outflow vessels that resulted from its septation showed differential lacZ expression. The ascending aorta was invested by lacZ-positive cells while the pulmonary trunk was devoid of lacZ staining. In the chick, both of these vessels were invested by neural crest cells, but the cells arrived secondarily by displacement from the aortic arch arteries during vessel elongation. This may indicate a difference in derivation of the pulmonary trunk in the mouse or a difference in distribution of cardiac neural crest cells. An independent mouse neural crest marker is needed to confirm whether the differences are indeed due to species differences in cardiovascular and/or neural crest development. Nevertheless, with the differences noted, we believe that this mouse model faithfully represents the location of cardiac neural crest cells. The similarities in location of lacZ-expressing cells in the mouse to that of cardiac neural crest cells in the chick suggest that this mouse is a good model for studying mammalian cardiac neural crest and that the mammalian cardiac neural crest performs functions similar to those shown for chick
Multiple Mechanisms Contribute to the Avoidance of Avian Epidermis by Sensory Axons

AbstractIn birds, sensory innervation of skin is restricted to dermis, with few axons penetrating into the epidermis. This pattern of innervation is maintainedin vitro,where sensory neurites avoid explants of epidermis but grow readily on dermis. We have used this coculture paradigm to investigate the mechanisms that impede innervation of avian epidermis. The lack of epidermal innervation in birds has been attributed to diffusible chondroitin sulfate proteoglycans (CSPGs) secreted by the epidermis, although direct experimental evidence is weak. We found that elimination of CSPG function with either chondroitinase or neutralizing antibodies did not promote growth of DRG neurites onto epidermisin vitro,indicating that CSPGs alone are not responsible for preventing epidermal innervation. Moreover, the failure of sensory neurites to invade epidermis is not due exclusively to soluble chemorepulsive factors, since sensory neurites also avoid dead epidermis. This inhibition can be overridden, however, by coating epidermis with the growth-promoting molecule laminin, but only if the tissue is killed first. Epidermal innervation of laminin-coated epidermis is even more robust when CSPGs are also eliminated. Thus, the absence of growth-promoting or permissive molecules, such as laminin, may contribute to the failure of sensory neurites to invade avian epidermis. Together these results show that the inhibitory character of avian epidermis is complex. Cell- or matrix-associated CSPGs clearly contribute to the inhibition, but are not solely responsible
Microsatellite Loci in Wild-Type and InbredStrongylocentrotus purpuratus

AbstractStrongylocentrotus purpuratus,a major research model in developmental molecular biology, has been inbred through six generations of sibling matings. Though viability initially decreased, as described earlier, the inbred line now consists of healthy, fertile animals. These are intended to serve as a genomic resource in which the level of polymorphism is decreased with respect to wildS. purpuratus.To genotype the inbred animals eight simple sequence genomic repeats were isolated, in context, and PCR primers were generated against the flanking single-copy sequences. Distribution and polymorphism of these regions of the genome were studied in the genomes of 27 wild individuals and in a sample of the inbred animals at F2 and F3 generations. All eight regions were polymorphic, though to different extents, and their homozygosity was increased by inbreeding as expected. The eight markers suffice to identify unambiguously the cellular DNA of any wild or F3S. purpuratusindividual
Time Course of Ion Channel Development inXenopusMuscle Inducedin Vitroby Activin

AbstractDuring the process of mesoderm specification inXenopusembryos, cells of the equatorial region are induced to form mesoderm in response to signals from the underlying endodermal cells. One mesodermal cell type resulting from thisin vivoinduction is skeletal muscle, which has a very specific and tightly regulated course of electrical and morphological development. Previously, electrical development could be analyzed only after neurulation, once myocytes could be morphologically identified.In vitro,activin triggers a cascade of events leading to the development of specific mesodermal tissues, including skeletal muscle; however, the precise role of activinin vivois less clear. Much is now known about the mechanism and control of activin action, but very little is known about the subsequent time course of differentiation of activin-induced muscle. Such muscle is routinely identified by the presence of a small number of specific markers which, although they accurately confirm the presence of muscle, give little indication of the time course or quantitative aspects of muscle development. One of the most important functional aspects of muscle development is the acquisition of the complex electrical properties which allow it to function normally. Here we assess the ability of activin to drivein vitrothe normal highly regulated sequence of electrical development in skeletal muscle. We find that in most, but not all, respects the normal time course of development of voltage-gated ion currents is well reproduced in activin-induced muscle. This characterization strengthens the case for activin as an agent capable of inducing the detailed developmental program of muscle and now allows for analysis of the regulation of electrical development prior to neurulation
Murine Fibroblast Growth Factor Receptor 1α Isoforms Mediate Node Regression and Are Essential for Posterior Mesoderm Development

AbstractAlternative splicing in the fibroblast growth factor receptor 1 (Fgfr1) locus generates a variety of splicing isoforms, including FGFR1α isoforms, which contain three immunoglobulin-like loops in the extracellular domain of the receptor. It has been previously shown that embryos carrying targeted disruptions of all major isoforms die during gastrulation, displaying severe growth retardation and defective mesodermal structures. Here we selectively disrupted the FGFR1α isoforms and found that they play an essential role in posterior mesoderm formation during gastrulation. We show that the mutant embryos lack caudal somites, develop spina bifida, and die at 9.5–12.5 days of embryonic development because they are unable to establish embryonic circulation. The primary defect is a failure of axial mesoderm cell migration toward the posterior portions of the embryos during gastrulation, as revealed by regional marker analysis and DiI labeling. In contrast, the anterior migration of the notochord is unaffected and the embryonic structures rostral to the forelimb are relatively normal. These data demonstrate that FGF/FGFR1α signals are posteriorizing factors that control node regression and posterior embryonic development
Developmental Competence of the Gut Endoderm: Genetic Potentiation by GATA and HNF3/Fork Head Proteins

AbstractA long-standing problem in developmental biology has been to understand how the embryonic germ layers gain the competence to differentiate into distinct cell types. Genetic studies have shown that members of the GATA and HNF3/fork head transcription factor families are essential for the formation and differentiation of gut endoderm tissues in worms, flies, and mammals. Recentin vivofootprinting studies have shown that GATA and HNF3 binding sites in chromatin are occupied on a silent gene in endoderm that has the potential to be activated solely in that germ layer. These and other data indicate that these evolutionarily conserved factors help impart the competence of a gene to be activated in development, a phenomenon calledgenetic potentiation.The mechanistic implications of genetic potentiation and its general significance are discussed
Prostate Development Requires Sonic Hedgehog Expressed by the Urogenital Sinus Epithelium

AbstractThe prostate gland develops from the urogenital sinus by a testosterone-dependent process of ductal morphogenesis.Sonic hedgehog(Shh) is expressed in the urogenital sinus epithelium and the time course of expression coincides with the formation of the main prostatic ducts. Expression is most abundant in the lumen of the urogenital sinus and in the contiguous proximal duct segments. The initial upregulation ofShhexpression in the male urogenital sinus depends on the presence of testosterone. The function of Shh was examined in the male urogenital sinus which was transplanted under the renal capsule of an adult male host mouse. Blockade of Shh function by a neutralizing antibody interferes with Shh signaling and abrogates growth and ductal morphogenesis in the transplanted tissue. These observations show that testosterone-dependentShhexpression in the urogenital sinus is necessary for the initiation of prostate development
Zebrafish in Context: Uses of a Laboratory Model in Comparative Studies

AbstractWith the recent interest in the reintegration of evolutionary and developmental biology has come a growing need for understanding the phylogenetic relations and degree of generality of the model organisms upon which we rely so heavily. In vertebrate biology the zebrafishDanio reriohas become a paradigmatic system for studies at levels of organization from molecular to interspecific. Studies of model systems in development are often techniques-driven rather than questions-based; however, informative hypotheses for developmental research can be derived from phylogenetic distributions of characters. With some understanding of how general the characters of interest are, a thoughtful comparison of the requirements of the questions with the lists of available embryos, reagents, and protocols can guide choices of new vertebrate models. We describe here the phylogenetic placement of zebrafish within the vertebrate world and discuss how generally observations on zebrafish can be taken to apply. We outline a practical protocol for investigating development in a comparative context, illustrated with an example from an ongoing study of teleost tail fin evolution. The principles and procedures presented here apply equally well to any comparative study with an interest in evolution, at any level of phylogeny from intraspecific studies to comparisons across phyla
Two Structural Variants of Nek2 Kinase, Termed Nek2A and Nek2B, Are Differentially Expressed inXenopusTissues and Development

AbstractNek2 kinase, a NIMA-related kinase, has been suggested to play both meiotic and mitotic roles in mammals, but its function(s) during development is poorly understood. We have isolated here cDNAs encoding aXenopushomolog of mammalian Nek2 and have shown thatXenopusNek2 has two structural variants, termed Nek2A and Nek2B. Nek2A, most likely a C-terminally spliced form, corresponds to the previously described human and mouse Nek2, while Nek2B is most probably a novel, C-terminally unspliced form of Nek2. As a consequence of this (probable) alternative splicing, Nek2B lacks the C-terminal 70-amino-acid sequence of Nek2A, which contains a PEST sequence (or a motif for rapid degradation). Western blot analysis reveals that Nek2A is expressed predominantly in the testis (presumably in spermatocytes) and very weakly in the stomach and, during development, only after the neurula stage. By contrast, Nek2B is expressed mainly in the ovary and in both primary and secondary oocytes and early embryos up to the neurula stage. These results suggest that Nek2A and Nek2B may play both meiotic and mitotic roles, but in a spatially and temporally complementary manner duringXenopusdevelopment, and that Nek2B, rather than Nek2A (or the conventional form of Nek2), may play an important role in early development. We discuss the possibility that a counterpart ofXenopusNek2B might also exist and function in early mammalian development
Spatiotemporal Dynamics of the [Ca2+]iRise Induced by Microinjection of Sperm Extract into Mouse Eggs: Preferential Induction of a Ca2+Wave from the Cortex Mediated by the Inositol 1,4,5-Trisphosphate Receptor

AbstractHamster sperm extract (SE) possessing Ca2+oscillation-inducing activity was microinjected into the peripheral or central region of mouse eggs, and the first increase in intracellular Ca2+concentration ([Ca2+]i), together with the spread of fluorescence-labeled SE in the ooplasm, was investigated by imaging with confocal microscopy. Injection into the periphery always induced a Ca2+wave that started from the injection site after a delay of 5 to 30 s depending on the concentration of SE. The diluted SE caused a wave of two-step [Ca2+]irises, which was always observed at fertilization. Injection into the center could induce a radial Ca2+wave with relatively high dose of SE, but lower dose of SE caused a [Ca2+]irise after a longer delay which was initiated synchronously over the ooplasm or was preceded in a peripheral area. Injection of diluted SE remarkably prolonged the delay time and reduced the rate of [Ca2+]irise. The critical concentration of SE needed to induce [Ca2+]irise was significantly lower in the periphery. These results indicate that the sensitivity to SE is higher in the cortex. SE-induced [Ca2+]irises were blocked by an antibody against the type 1 inositol 1,4,5-trisphosphate receptor (InsP3R). The cortex was substantially more sensitive to injected InsP3induction of Ca2+release than the center. It is suggested that the cortex of mouse eggs may involve a functionally specialized organization of InsP3Rs and Ca2+pools in which a cytosolic sperm factor(s) could act upon sperm–egg fusion to cause Ca2+release, leading to the Ca2+wave at fertilization
Defects in Tracheoesophageal and Lung Morphogenesis inNkx2.1(−/−) Mouse Embryos

AbstractNKX2.1 is a homeodomain transcriptional factor expressed in thyroid, lung, and parts of the brain. We demonstrate that septation of the anterior foregut along the dorsoventral axis, into distinct tracheal and esophageal structures, is blocked in mouse embryos carrying a homozygous targeted disruption of theNkx2.1locus. This is consistent with the loss ofNkx2.1expression, which defines the dorsoventral boundary within the anterior foregut in wild-type E9 embryos. Failure in septation between the trachea and the esophagus inNkx2.1(−/−) mice leads to the formation of a common lumen that connects the pharynx to the stomach, serving both as trachea and as esophagus, similar in phenotype to a human pathologic condition termed tracheoesophageal fistula. The main-stem bronchi bifurcate from this common structure and connect to profoundly hypoplastic lungs. The mutant lungs fail to undergo normal branching embryogenesis, consist of highly dilated sacs that are not capable of sustaining normal gas exchange functions, and lead to immediate postnatal death.In situhybridization suggests reducedBmp-4expression in the mutant lung epithelium, providing a possible mechanistic clue for impaired branching. Functional deletion ofNkx2.1blocks pulmonary-specific epithelial cell differentiation marked by the absence of pulmonary surfactant protein gene expression. Altered expression of temporally regulated genes such asVegfdemonstrates that the lung inNkx2.1(−/−) mutant embryos is arrested at early pseudoglandular (E11–E15) stage. These results demonstrate a critical role forNkx2.1in morphogenesis of the anterior foregut and the lung as well as in differentiation of pulmonary epithelial cells