ANALYSIS OF TENASCIN MESSENGER-RNA EXPRESSION IN THE MURINE MAMMARY-GLAND FROM EMBRYOGENESIS TO CARCINOGENESIS - AN IN-SITU HYBRIDIZATION STUDY

The expression of tenascin gene during murine mammary gland developmen t was analyzed by in situ hybridization with non-radioactive cRNA prob es. 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 an d 15th day of gestation, and in the mesenchymal cells from the 14th da y to the 17th day, at the epithelial-mesenchymal border of the growing bud. However, cells displaying tenascin mRNAs were not found beyond t he bifurcation of the mammary sprout at the beginning of the branching morphogenesis. In post-natal development, tenascin mRNAs were demonst rated in mesenchymal cells surrounding end buds in juvenile mice, in m esenchymal cells surrounding the epithelial cells of plaques, in epith elial cells of the lactating mammary gland, in malignant epithelial ce lls and in the mesenchymal cells surrounding cancer nests. By immunohi stochemistry, tenascin immunoreactivity was shown to have the same spa tiotemporal distribution as that of tenascin mRNAs, but was observed t o be restricted to the stroma, except in the lactating mammary gland w here tenascin was demonstrated in the milk by Western blot. The presen t study thus showed that both epithelial and mesenchymal cells are sou rces of tenascin at different stages of murine mammary gland developme nt.