OZF gene expression in growing mouse and rabbit mammary gland and in rabbit mammary cells and Nb2 cells under prolactin action.

The OZF gene identified recently is expressed in a few cell types and particularly in mammary cell but not in fibroblasts. This gene is expressed more abundantly in several mammary tumor cell lines than in normal cells. In the present work, OZF mRNA concentration was evaluated in rabbit and mouse mammary gland during the pregnancy-lactation-weaning cycle. The OZF mRNA concentration was at its highest level during the first part of pregnancy and decreased at parturition. It was maintained at its lowest level throughout lactation. Prolactin which induces mammary gland growth and milk synthesis in vivo did not stimulate OZF gene expression. In the Nb2 lymphoid cell line, prolactin, which is a compulsory growth factor, did not alter OZF mRNA concentration. These data suggest that OZF may be involved in some way in mammary gland growth. Moreover, OZF does not appear to be a key gene for the induction of cell multiplication. OZF gene expression might negatively control, to some extent, mammary cell differentiation.