Analysis of tenascin mRNA expression in the murine mammary gland from embryogenesis to carcinogenesis: an in situ hybridization study.

The expression of tenascin gene during murine mammary gland development was analyzed by in situ hybridization with non-radioactive cRNA probes. The aim was to identify whether cells that synthesize tenascin are mesenchymal or epithelial. During embryogenesis, tenascin mRNAs were demonstrated in the epithelial cells of the mammary bud on the 14th and 15th day of gestation, and in the mesenchymal cells from the 14th day to the 17th day, at the epithelial-mesenchymal border of the growing bud. However, cells displaying tenascin mRNAs were not found beyond the bifurcation of the mammary sprout at the beginning of the branching morphogenesis. In post-natal development, tenascin mRNAs were demonstrated in mesenchymal cells surrounding end buds in juvenile mice, in mesenchymal cells surrounding the epithelial cells of plaques, in epithelial cells of the lactating mammary gland, in malignant epithelial cells and in the mesenchymal cells surrounding cancer nests. By immunohistochemistry, tenascin immunoreactivity was shown to have the same spatiotemporal distribution as that of tenascin mRNAs, but was observed to be restricted to the stroma, except in the lactating mammary gland where tenascin was demonstrated in the milk by Western blot. The present study thus showed that both epithelial and mesenchymal cells are sources of tenascin at different stages of murine mammary gland development.