Regulation of milk protein gene expression

Studies using both transgenic mice and transfected mammary epithelial cells have established that composite response elements containing multiple bind ing sites for several transcription factors mediate the hormonal and develo pmental regulation of milk protein gene expression, Activation of signal tr ansduction pathways by lactogenic hormones and cell-substratum interactions activate transcription factors and change chromatin structure and milk pro tein gene expression. The casein promoters have binding sites for signal tr ansducers and activators of transcription 5, Yin Yang 1, CCAAT/enhancer bin ding protein, and the glucocorticoid receptor. The whey protein gene promot ers have binding sites for nuclear factor I, as well as the glucocorticoid receptor and the signal transducers and activators of transcription 5. The functional importance of some of these factors in mammary gland development and milk protein gene expression has been elucidated by studying mice in w hich some of these factors have been deleted.