(a) Growth rate of pups from WT and MK-PTEN mice. Newborns from WT and MK-PTEN mothers were weighed each day for 2 weeks. Data are expressed as the mean ± SD of 16 MK-PTEN pups nursing with either an MK-PTEN or a WT mother, as indicated. (b) Milk protein mRNA expression in mammary glands of MK-PTEN and WT mice. Total RNA was isolated from mammary glands of WT and MK-PTEN at days 9 and 14 of pregnancy. Northern blot analysis was performed using probes corresponding to cDNAs of various milk proteins, as indicated. Blots were stripped and reprobed with an 18S probe as a loading control and with K18 as a marker of epithelial cells. Each lane represents a single animal. Similar results were obtained with a total of four WT and four MK-PTEN mice.