Expression of type 1 and 2A protein phosphatase subunits in the rat corpus luteum across pregnancy.

This study was undertaken to test the hypothesis that the reduction in protein phosphatase activity that had been observed at mid-pregnancy in the rat corpus luteum (CL) was due to a decrease in expression of one of the catalytic subunits or an increase in one of the B regulatory subunits of the type 2A protein phosphatase (PP2A). Ovaries were collected from rats on days (d) 1, 3, 7, 14, 20, and 21 of pregnancy, and on day 21 after progesterone treatment on day 20 (nZ6). Realtime RT-PCR was used to analyze the expression of the a and b isoforms of the catalytic subunit, the structural A subunit, and three B regulatory subunits of PP2A, as well as the catalytic subunit of PP1. Expression of the a and b catalytic subunits of PP2A was progesterone responsive. Expression of the PP1 catalytic subunit correlated with the previously reported protein phosphatase activity, but PP2A subunits did not. The data suggest that the decreased protein phosphatase activity at mid-pregnancy was due to a decline in expression of the catalytic subunits of PP1 rather than changes in expression of PP2A subunits.