In situ hybridization--a useful tool for studies on collagen gene expression in cell culture as well as in normal and altered tissue.

We report the application of antisense RNA probes for in situ hybridization to identify collagen type I and type III mRNA synthesizing fibroblasts under in vitro and in vivo conditions in normal and wounded human skin. Non-specific hybridization was excluded by specific distribution patterns of alpha 1(I)- and alpha 1(III) probes in mouse fetuses. In addition, the specificity of hybridization was checked by sense probes, radioactively labelled transcripts of Gemini vectors and a keratin probe. In normal skin weakly activated fibroblasts were sparsely scattered within the dermis, while in wound healing processes mRNA both for alpha 1(I) and for alpha 1(III) was dramatically increased, thus suggesting that collagen synthesis is at least partly regulated at a pretranslational level. In addition, the intensity of the labelling, as defined by image analysis and the distribution pattern of collagen mRNA synthesizing cells, provide strong evidence that wound healing by primary intention starts within the deep dermis.