Expression of CDK inhibitor (CDI) p57 and bcl-2 mRNA during follicular development and follicular atresia in the rat ovary

Cho, Gyeong Jae; Koh, Phil Ok; Kwak, Soo Dong; Kim, Myeong Ok; Lee, Bong Hee; Choi, Wan Sung; Baik, Sang Ho

Abstract

In mammals, the ovary proceeds follicular development and atresia during the reproductive cycle. Follicular atresia occurs through apoptosis, programmed cell death (PCD) which is mediated by gene controlling apoptosis and cell cycle. Regulatory genes of apoptosis and cell cycle have previously reported. Recently, the products of bcl-2, bax, Fas, and TNF-a genes were reported to play critical roles in apoptosis, and the products of p21, p27, p57, and p53 genes were known to play many roles in cell cycle. In these genes, bcl-2 is known as a apoptosis inhibitor in the ovary, while p57 which was recently reported to express in the testis and other several organs, is a cyclin dependent kinase inhibitor (CDI). We thought that these genes are associated with follicular development and atresia. Therefore, the present study used a in situ hybridization to examine the expression of these two genes, followed by synthesis of a radioisotope labelled cRNA probes during PMSG-induced follicular development and atresia in the immature rat ovary. Morphological changes were occurred with the manner of 5 days periodicity after PMSG treatment. 1 or 2 days after PMSG treatment, the ovaries have showed growing follicles with antrum and healthy granulosa cells. The ovaries of 3 days after treatment were appeared continuous growing follicles and some degenerating follicles which had thinner granulosa cell layers than growing follicles. But the ovaries of 4 or 5 days have showed degenerating follicles which have pyknotic nuclei and thin distorted granulosa cell layers. These atretic follicles showed positive reaction with DNA end labelling method indicating apoptotic processes. In situ hybridization signals to p57 cRNA probe were expressed in the theca externa cells of the control ovary. In PMSG treated 4 or 5 days ovaries, the atretic follicles have showed stronger signals than 1 or 2 days growing ovarian follicles. But the signals to bcl-2 cRNA probe were expressed in the ovarian theca and interstitial cells including theca basement membrane. And this signals were decreased in the 4 or 5 days atretic follicles and interstitium. According to these data, we suggest that these two genes are associated to follicular development and atresia via individual up- and down regulatory mechanism.