PARENT SESSION
Gene Regulation & Function

THE CASEIN MRNA DECAY IS REGULATED THROUGH THE POLYADENYLATION PATHWAY IN THE MOUSE MAMMARY GLAND DURING PREGNANCY AND LACTATION.

Kuraishi, Takeshi¹, Mizoguchi, Yasushi¹, Suzuki, Toshiyuki¹, Aoki, Fugaku¹, Sakai, Senkiti¹, ¹

ABSTRACT- We found that the poly(A) tail length of casein mRNA was abruptly elongated from late pregnancy to early lactation in the mouse mammary gland. Furthermore we showed that casein mRNA with the longer poly(A) tail had a longer half-life in mammary tissues culture. These results indicated that the casein mRNA decay was regulated by changing the poly(A) tail length. It is known that the poly(A) tail is added to the 3'-end of pre-mRNA with poly(A) polymerase (PAP) in the nucleus. In this study, in order to investigate whether PAP was related to the mechanism to regulate the poly(A) tail length, we examined the amount of PAP mRNA during pregnancy and lactation by using competitive RT-PCR, and the results are expressed on a basis of tissue DNA (amol/mg DNA). The PAP mRNA level abruptly increased from 72.7+/-5.4 (M+/-SE) on day 17 of pregnancy to 148.5+/-1.3 on the day of parturition, and peaked on the day of parturition. Although the PAP mRNA level was maintained relatively high during the first half of lactation, it declined consistently toward the end of lactation. The level of PAP mRNA was 32.1+/-9.9 on day 18 of lactation, and it was lower than that on day 17 of pregnancy. The changing profile of PAP mRNA level was highly correlated with that of the poly(A) tail length of casein mRNA during pregnancy and lactation (r=0.93). It is concluded that the casein mRNA decay was regulated by the change in the poly(A) tail length through the manipulation of the PAP gene expression in the mouse mammary gland during pregnancy and lactation.

KEY WORDS: mammary gland, poly(A) polymerase, casein