Non-coordinate expression of closely linked mouse casein genes

Expression levels of five mouse casein genes were analysed in the mammary gland of virgin, pregnant and lactating mice. We have already shown that the five murine casein genes are arranged in the order, α-(-γ-e-κ in a tandem array, very close to each other in a 250 kb DNA fragment of mouse genome. Northern blot analysis showed that, of the calcium-sensitive casein genes, the e casein gene is expressed only during lactation unlike the a, (and y casein genes which are expressed during pregnancy and lactation. Even though the a, ( and y genes exhibited a co-ordinated expression pattern from mid to the later stages of pregnancy, the mRNA levels varied considerably (60, 90 and 100% respectively) by the onset of lactation. The mRNA level of the calcium-insensitive K casein gene increased from mid-pregnancy but at a lower rate and reached 60% by the first day of lactation. Considering the locations and closeness of the casein genes, a non-coordinate expression profile is exhibited by the mouse casein genes, particularly the e casein gene.