Changes in location of type I collagen synthesis in two stages of fetal calf skin as revealed by in situ hybridization.

The distribution of sites of type I collagen gene expression was studied in frozen sections of skin of 4 and 9 month-old calf fetuses by in situ hybridization using a human pro-alpha 1 type I collagen cDNA. The labelling varied with the different layers of the dermis and with the developmental stage considered. In the 4 month old fetus skin, the label appeared concentrated in the upper layer of the dermis at the lewel of the hair follicles. In the 9 month-old fetus skin, the difference of labelling between upper papillary dermis and lower dermis was less marked. Comparatively the distribution of the extracellular type I collagen was determined by indirect immunofluorescence. This collagen appeared present throughout the whole dermis with slight variations at 4 months, where there was less extracellular collagen near the hair bulbs. These results are in agreement with the idea that the collagen synthesis follows cutaneous differentiation. In addition, they support the hypothesis that collagen is deposited once morphogenetic events have occurred and plays thus a stabilizing role in formation of cutaneous appendages.