After cessation of lactation, the mammary gland undergoes involution, regressing to a state resembling that of a virgin animal. This phase of mammary gland development is characterized by epithelial cell death and tissue remodeling. To understand molecular mechanisms of mammary gland involution, we identified involution-induced clones by differential screening of a mouse mammary gland cDNA library. Several known genes were induced during mammary gland involution: sulfated glycoprotein-2 (SGP-2), WDNM1, lactoferrin, ferritin heavy chain (FHC), lysozyme and osteopontin genes. Involution of the mammary gland is presumed to be mediated by a decrease in serum prolactin level induced by weaning, but may also involve changes in paracrine or autocrine growth factors. Effects of lactogenic hormones and EGF on the expression of the involution-induced genes were examined in mammary epithelial cells. Insulin, dexamethasone, and prolactin did not influence the expression of the FHC, WDNM1 and SGP-2 genes. However, EGF strongly inhibited the expression of WDNM1 and SGP-2 genes. Our recent results are reviewed and discussed.

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