Article Abstract:
Studying wound healing is a way of studying an important part of embryonic morphogenesis, namely, the tissue movements of epithelial spreading and mesenchymal contraction. Studies conducted on the limb bud stage mouse embryo using DiI labelled mesenchymal cells in an excisional lesion made on the limb bud show that mesenchymal contraction and reepithelialisation contribute equally to healing. Reepithelialisation takes place by purse-string contractions of a cable of filamentous actin while in adult wounds it is by lamellipodial crawling. Contraction of the connective tissue in adult wounds is by the conversion of dermal fibroblasts into myofibroblast but this process is not seen in the embryo wound healing.
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Article Abstract:
The factors responsible for cleavage asynchrony in the Tubifex embryo, in which the AB-cell divides much later than the CD-cell, were examined. Chromosome cycle studies revealed that AB-cells underwent M-phase five minutes after the CD-cell and that its prometaphase portion lasted 25 minutes longer. The length of the AB nucleus' prometaphase was reduced significantly only after the mitotic spindles of AB and CD nuclei, in a common cytoplasm, were united at one pole. Asters did not play any role in AB-cell mitotic spindle assembly. Results suggest that cleavage asynchrony in the embryo is caused by both cytoplasmic and nucleus-associated factors.
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Article Abstract:
A study involving cloning and characterization of the chick HNF-3beta gene and its pattern of expression in midline neural plate cells showed that the notochord can induce ectopic neural expression of HNF-3beta gene in vivo and in vitro. In addition, the expression by neural plate cells occurs in direct response to induction signaled by the notochord. HNF-3beta expression, floor plate differentiation and floor plate development are discussed.
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