WNT11 promotes cardiac tissue formation of early mesoderm.
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Cardiac tissue in the bird is derived from paired regions of lateral mesoderm within the anterior half of the embryo (Rawles [1943] Physiol. Zool. 16:22-42; Stalsberg and DeHaan [1969] Dev. Biol. 19:128-159). Previously, we reported that WNT11 is expressed in early avian mesoderm in a pattern that overlaps with the precardiac regions. To examine whether this molecule may play a role in promoting cardiogenesis, we cultured tissue explants from microdissected HH stage 4, 5, and 6 quail embryos. The isolated tissue consisted of both the mesoderm and endoderm layers from either anterior precardiac or posterior noncardiogenic regions of the embryo. As a necessary control for examining the ability of WNT11 to convert noncardiogenic mesoderm to cardiac tissue, we compared the cardiogenic potential of anterior and posterior regions. For stages 5 and 6, our results were consistent with what has been previously reported (Rawles [1943] Physiol. Zool. 16:22-42; Sugi and Lough [1994] Dev. Dyn. 200:155-162); as anterior mesoderm becomes contractile, while posterior mesoderm does not produce cardiac tissue. Surprisingly, when we examined stage 4 embryos both anterior and posterior regions gave rise to cardiac tissue in culture. To determine whether WNT11 could promote cardiac differentiation in tissue that was noncardiogenic, this molecule was ectopically expressed or added to mesoderm/endoderm explants obtained from stage 5 or 6 posterior tissue. Transfection of stage 5 posterior tissue with a WNT11 expression plasmid provoked the appearance of cardiomyocytes in 33% of the explants; half of which were contractile. Similarly transfected stage 6 posterior explants did not demonstrate cardiac differentiation. More dramatic results were obtained when noncardiogenic tissue was exposed to conditioned media containing soluble WNT11; as 63% and 33% of posterior stage 5- or stage 6-derived explants underwent cardiac differentiation. Together, these results indicate that WNT11 can promote cardiac development within noncardiac tissue. The expression of WNT11 in anterior mesoderm of early gastrula stage embryos suggests it may play a role in the formation of the vertebrate heart. Dev Dyn 1999;216:45-58. (+info)
Characterization of the early development of specific hypaxial muscles from the ventrolateral myotome.
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We have previously found that the myotome is formed by a first wave of pioneer cells generated along the medial epithelial somite and a second wave emanating from the dorsomedial lip (DML), rostral and caudal edges of the dermomyotome (Kahane, N., Cinnamon, Y. and Kalcheim, C. (1998a) Mech. Dev. 74, 59-73; Kahane, N., Cinnamon, Y. and Kalcheim, C. (1998b) Development 125, 4259-4271). In this study, we have addressed the development and precise fate of the ventrolateral lip (VLL) in non-limb regions of the axis. To this end, fluorescent vital dyes were iontophoretically injected in the center of the VLL and the translocation of labeled cells was followed by confocal microscopy. VLL-derived cells colonized the ventrolateral portion of the myotome. This occurred following an early longitudinal cell translocation along the medial boundary until reaching the rostral or caudal dermomyotome lips from which fibers emerged into the myotome. Thus, the behavior of VLL cells parallels that of their DML counterparts which colonize the opposite, dorsomedial portion of the myotome. To precisely understand the way the myotome expands, we addressed the early generation of hypaxial intercostal muscles. We found that intercostal muscles were formed by VLL-derived fibers that intermingled with fibers emerging from the ventrolateral aspect of both rostral and caudal edges of the dermomyotome. Notably, hypaxial intercostal muscles also contained pioneer myofibers (first wave) showing for the first time that lateral myotome-derived muscles contain a fundamental component of fibers generated in the medial domain of the somite. In addition, we show that during myotome growth and evolution into muscle, second-wave myofibers progressively intercalate between the pioneer fibers, suggesting a constant mode of myotomal expansion in its dorsomedial to ventrolateral extent. This further suggests that specific hypaxial muscles develop following a consistent ventral expansion of a 'compound myotome' into the somatopleure. (+info)
The role of the rhombic lip in avian cerebellum development.
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We have used a combination of quail-chick fate-mapping techniques and dye labelling to investigate the development of the avian cerebellum. Using Hoxa2 as a guide for the microsurgical construction of quail-chick chimaeras, we show that the caudal boundary of the presumptive cerebellum at E6 maps to the caudal boundary of rhombomere 1. By fate mapping the dorsoventral axis of rhombomere 1, we demonstrate that granule cell precursors are generated at the rhombic lip together with neurons of the lateral pontine nucleus. DiI-labelling of cerebellum explants reveals that external germinal layer precursors have a characteristic unipolar morphology and undergo an orientated, active migration away from the rhombic lip, which is apparently independent of either glial or axon guidance or 'chain' formation. (+info)
Induction of syncytia by neuropathogenic murine leukemia viruses depends on receptor density, host cell determinants, and the intrinsic fusion potential of envelope protein.
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Infection by the neuropathogenic murine leukemia virus (MLV) TR1.3 results in hemorrhagic disease that correlates directly to in vivo syncytium formation of brain capillary endothelial cells (BCEC). This phenotype maps to amino acid 102 in the envelope (Env) protein of TR1.3. Substitution of glycine (G) for tryptophan (W) at this position (W102G Env) in the nonpathogenic MLV FB29 induces both syncytium formation and neurologic disease in vivo. Using an in vitro gene reporter cell fusion assay, we showed that fusion either with murine NIH 3T3 cells or with nonmurine target cells that expressed receptors at or below endogenous murine levels mirrored that seen in BCEC in vivo. In these instances only TR1.3 and W102G Env induced cell fusion. In contrast, when receptor levels on nonmurine cells were raised above endogenous murine levels, FB29 Env was as fusogenic as the neuropathogenic TR1.3 and W102G Env. These results indicate that TR1.3 Env and W102G Env are intrinsically more fusogenic than FB29 Env, that the induction of fusion requires a threshold number of receptors that is greater for FB29 Env than for TR1.3 or W102G Env, and that receptor density on murine NIH 3T3 cells and BCEC is below the threshold for FB29-dependent fusion. Surprisingly, receptor density on NIH 3T3 cells could not be increased by stable expression of exogenous receptors, and FB29-dependent fusion was not observed in NIH 3T3 cells that transiently expressed elevated receptor numbers. These results suggest that an additional undefined host cell factor(s) may limit both receptor expression and fusion potential in murine cells. (+info)
Growth, developmental stability and immune response in juvenile Japanese quails (Coturnix coturnix japonica).
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Stresses are environmental factors which restrict growth or cause a potentially adverse change in an organism. The exposure of developing organisms to environmental stresses may have several physiological consequences including a decrease in immunocompetence. However, mounting an immune response against a foreign antigen may in itself constitute a cost for developing organisms. This cost has potentially long-term consequences for adult function and fitness. This study examines the growth and developmental stability of Japanese quail++ chicks challenged by three non-pathogenic antigens: sheep red blood cells, which assess T-cell-dependent immune responses, and Mycoplasma synoviae and Newcastle disease virus, which assess T-cell-independent responses. Increases in both body mass and wing length were significantly reduced in antigen-challenged birds compared to control birds. Fluctuating asymmetry (FA) in the masses of primary feathers increased from the innermost (1) to the outermost (10) position on the wing. In addition, antigen challenge by M. synoviae and sheep red blood cells was associated with an increase in FA. The cell-mediated response measured by reaction to phytohaemagglutinin was significantly depressed in M. synoviae-challenged birds. White blood cell counts, except for monocytes, were elevated in response to all three antigen treatments. Total plasma protein and haematocrit also differed between treatments but exhibited no clear relationship to antigen challenge. Immune responses clearly impose a stress on developing chicks. Additional research will be required to determine the long-term consequences of developmental stress and assess the selective forces that influence the strength of the immune responses of chicks. (+info)
Defining subregions of Hensen's node essential for caudalward movement, midline development and cell survival.
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Hensen's node, also called the chordoneural hinge in the tail bud, is a group of cells that constitutes the organizer of the avian embryo and that expresses the gene HNF-3(&bgr;). During gastrulation and neurulation, it undergoes a rostral-to-caudal movement as the embryo elongates. Labeling of Hensen's node by the quail-chick chimera system has shown that, while moving caudally, Hensen's node leaves in its wake not only the notochord but also the floor plate and a longitudinal strand of dorsal endodermal cells. In this work, we demonstrate that the node can be divided into functionally distinct subregions. Caudalward migration of the node depends on the presence of the most posterior region, which is closely apposed to the anterior portion of the primitive streak as defined by expression of the T-box gene Ch-Tbx6L. We call this region the axial-paraxial hinge because it corresponds to the junction of the presumptive midline axial structures (notochord and floor plate) and the paraxial mesoderm. We propose that the axial-paraxial hinge is the equivalent of the neuroenteric canal of other vertebrates such as Xenopus. Blocking the caudal movement of Hensen's node at the 5- to 6-somite stage by removing the axial-paraxial hinge deprives the embryo of midline structures caudal to the brachial level, but does not prevent formation of the neural tube and mesoderm located posteriorly. However, the whole embryonic region generated posterior to the level of Hensen's node arrest undergoes widespread apoptosis within the next 24 hours. Hensen's node-derived structures (notochord and floor plate) thus appear to produce maintenance factor(s) that ensures the survival and further development of adjacent tissues. (+info)
SF/HGF is a mediator between limb patterning and muscle development.
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Scatter factor/hepatocyte growth factor (SF/HGF) is known to be involved in the detachment of myogenic precursor cells from the lateral dermomyotomes and their subsequent migration into the newly formed limb buds. As yet, however, nothing has been known about the role of the persistent expression of SF/HGF in the limb bud mesenchyme during later stages of limb bud development. To test for a potential role of SF/HGF in early limb muscle patterning, we examined the regulation of SF/HGF expression in the limb bud as well as the influence of SF/HGF on direction control of myogenic precursor cells in limb bud mesenchyme. We demonstrate that SF/HGF expression is controlled by signals involved in limb bud patterning. In the absence of an apical ectodermal ridge (AER), no expression of SF/HGF in the limb bud is observed. However, FGF-2 application can rescue SF/HGF expression. Excision of the zone of polarizing activity (ZPA) results in ectopic and enhanced SF/HGF expression in the posterior limb bud mesenchyme. We could identify BMP-2 as a potential inhibitor of SF/HGF expression in the posterior limb bud mesenchyme. We further demonstrate that ZPA excision results in a shift of Pax-3-positive cells towards the posterior limb bud mesenchyme, indicating a role of the ZPA in positioning of the premuscle masses. Moreover, we present evidence that, in the limb bud mesenchyme, SF/HGF increases the motility of myogenic precursor cells and has a role in maintaining their undifferentiated state during migration. We present a model for a crucial role of SF/HGF during migration and early patterning of muscle precursor cells in the vertebrate limb. (+info)
Alterations of DNA-dependent DNA polymerase activities in the immature quail oviduct in response to estrogen stimulation.
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Administration of diethylstilbestrol, an estrogen analogue, to immature female quails causes an increase of extractable DNA-dependent DNA polymerase activities from the oviduct. At least two forms of polymerases have been determined, a high molecular weight polymerase (210,000 daltons) and a low molecular weight polymerase (34,000 daltons) calculated from column chromatography Sephadex G-200. During the primary hormone stimulation the amount of extractable enzyme reaches a maximum on the fifth day after daily injections of the hormone. In the period of withdrawal the activities decrease and reach values similar to those determined in the unstimulated oviducts. During secondary stimulation the polymerase activities increase again the first day; subsequently the values decrease drastically. The alterations in enzyme activity correlate with the DNA synthesis in the oviduct, as measured by analytical determination of the DNA content. (+info)