Involution of mouse mammary glands in whole organ culture: a model for studying programmed cell death.

The DNA fragmentation and gene expression patterns of involuting mouse mammary glands were compared to mammary glands in whole organ culture induced to involute by the withdrawal of lactogenic hormones. Non-random DNA degradation was observed both in vivo and in vitro, indicating that the withdrawal of lactogenic hormones triggers a program of epithelial cell death. Similar patterns of gene expression for the milk protein beta-casein and the apoptosis associated factors TGF-beta 1, TGF-beta 2 and TGF-beta 3 were observed in vivo and in vitro. These results indicate that the withdrawal of lactogenic hormones is responsible for decreased milk synthesis, epithelial cell death and tissue restructuring and that whole organ culture of mouse mammary glands is a useful model for studying the molecular events involved in these processes during involution.