Dietetics, Nutrition and Biological Sciences
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Item Analysis of the Tissue Movements of Embryonic Wound Healing-DiI Studies in the Limb Bud Stage Mouse Embryo(Elsevier, 1995-07) McCluskey, Jane T.; Martin, PaulThe tissue movements of epithelial spreading and mesenchymal contraction play key roles in many aspects of embryonic morphogenesis. One way of studying these movements in a controlled manner is to make an excisional skin wound to an embryo and watch the wound heal. In this paper we report our studies of healing of a simple excisional lesion made to the limb bud stage mouse embryo. The wounded, living embryo is cultured in a roller bottle; under such conditions the wound heals with a highly reproducible time course and is completely closed by 24 hr. During the healing period the environment bathing the wound can be simply manipulated by adding drugs or factors to the culture medium. We have used DiI to label mesenchymal cells exposed at the margin of the initial wound and, by following their fate and measuring the area of mesenchyme remaining exposed at various time points during the healing process, we have quantified both the extent of mesenchymal contraction and the extent of reepithelialisation by movement of epidermis over mesenchyme. We show that the two types of tissue movement contribute almost equally (50:50) to the total wound closure rate. We have gone on to investigate the cell machinery underlying these processes. In adult wounds the epidermis migrates by means of lamellipodial crawling, but we show that reepithelialisation in the embryo is achieved instead by purse-string contraction of a cable of filamentous actin which assembles in the basal layer of cells at the free edge of the epidermis. Addition of cytochalasin D to the culture medium blocks formation of this actin cable and leads to failure of reepithelialisation. Contraction of adult wound connective tissue appears to be driven by conversion of dermal fibroblasts into a specialist smooth muscle-like fibroblast, the myofibroblast. However, using an antibody recognising the alpha-isoform of smooth muscle actin and specific for smooth muscle cells and myofibroblasts, we show that a similar conversion into myofibroblasts does not occur at any stage during the embryonic wound healing process. These observations indicate that both of the tissue movements of embryonic wound healing utilise cell machinery fundamentally different from that driving the analogous tissue movements of adult healing.Item Repair of excisional wounds in the embryo(Nature Publishing Group, 1994) Martin, Paul; Nobes, Catherine; McCluskey, Jane T.; Lewis, JulianWound healing in the embryo, just as in the adult, comprises two tissue movements: re-epithelialisation and connective-tissue contraction. In this brief review we describe our recent studies of these two movements in both chick and rodent embryo model systems. In the chick we have evidence that the embryonic wound epidermis is drawn forwards by contraction of an actin pursestring extending around the circumference of the wound, rather than by lamellipodial crawling as in adult healing. Significant connective-tissue contraction also occurs. In the rat and mouse embryo we have examined expression of transcription factors and growth factors at the wound edge. We discuss our observations that the immediate-early gene c-fos and the growth factor transforming growth factor beta-1 are rapidly induced at the embryonic wound margin, and the possibility that these signals may trigger proliferation of wound edge cells and contraction of the exposed wound mesenchyme.Item A study of wound healing in the E11.5 mouse embryo by light and electron microscopy(Elsevier, 1993-04) McCluskey, Jane T.; Hopkinson-Woolley, James; Luke, Babara; Martin, PaulIn this paper we report our light and electron microscopic studies of the healing of a simple excisional lesion to the E11.5 mouse embryo hindlimb. The wounded living embryo is cultured in a roller bottle and under such conditions the lesion is completely re-covered with epithelium by 24 hr. We discuss how our studies of such a simple wound healing model may offer insight into the mechanisms of tissue repair generally.