Rapid induction and clearance of TGFβ1 is an early response to wounding in the mouse embryo

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Abstract
The TGFβ family of growth factors has been implicated as playing a significant role in many aspects of embryonic morphogenesis, and also as a mediator of adult tissue repair processes. Unlike the situation in the adult, rissue repair in the embryo does not result in scarring, and it has been suggested that this might be due, in part, to reduced levels of growth factors, particularly TGFβ, at the wound site. We have examined the expression patterns of TGFβ genes following wounding of limb bud lesions in cultured Ell.5 mouse embryos. The timetable of wound closure was investigated by standard light and electron microscopy from the time of wounding until the lesion had re-epithelialised 24 hours later. The expression of transcripts for each of the three TGFβ genes was examined at various time points during the healing process using radioactive in situ hybridisation to tissue sections and wholemount non-radioactive in situ hybridisation to embryo pieces. Within l to 3 hours of wounding, transcripts encoding TGFβl were rapidly induced within the epithelial cells of the wound margin, particularly those cells at the ventral aspect of the wound. By 3 to 6 hours post-wounding, TGFβl transcripts were detectable in the mesenchyme of the wound bed. No TGFβS induction was observed, and possible TGFβ2 induction was largely obscured by endogenous expression associated with pre-cartilage mesenchymal condensation. Immunocytochemical analysis of tissue sections of the wound demonstrated a rapid induction of TGFβl protein within l hour post-wounding, but also a subsequent rapid clearance of the protein from the wound site such that, by 18 hours post-wounding, TGFβl levels had returned to near background. These data are discussed in terms of the molecular mechanisms underlying embryonic wound healing and the significance of the results to an understanding of scarring following adult tissue repair. © 1993Wiley-Liss, Inc.