Fig. 3. Milk gene expression in wild-type (WT) and K5-N57-ßcat mammary glands estimated by semi-quantitative RT-PCR at different developmental stages. There are increased levels of ß-casein in 7.5-day-pregnant, increased levels of WAP and -lactalbumin (-LA) in 13.5-day-pregnant, and an accelerated decrease of ß-casein, WAP and -LA in involuting K5-N57-ßcat mouse mammary glands. 18S RNA was used as a normalization control for RT-PCR. P7.5, P10.5 and P13.5 correspond to 7.5, 10.5 and 13.5 days of pregnancy; L2 and L6, to 2 and 6 days of lactation; I3, to 3 days of involution.