Expression of bcl-2 and bax mRNAs during follicular development and atresia in the rat ovary

Koh, Phil Ok; Kang, Sang Soo; Choi, Wan Sung; Kwak, Soo Dong; Cho, Gyeong Jae

Abstract

In the mammalian ovary, follicular atresia occurs through apoptosis. Apoptosis is known as the physiological cell death, which is regulated by bcl-2 gene family. In the bcl-2 gene family, bcl-2/bcl-xLong is known as an inhibitor of apoptosis, whereas bax/bcl-xShort is known as an inducer of apoptosis. 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 bcl-2 and bax mRNAs during ovarian follicular development and atresia induced by PMSG (15 IU) treatment in the immature rat ovary. Morphological changes were occurred with the manner of five days periodicity after PMSG treatment. One or two days after PMSG treatment, ovaries had growing follicles with antrum and healthy granulosa cells. Three days after treatment, some degenerating follicles which had thinner granulosa cell layers than growing follicles were observed. At day four and five after treatment, degenerating follicles which have pyknotic nuclei and thin distorted granulosa cell layers appeared. These atretic follicles showed positive reaction with in situ DNA end labelling which indicates apoptotic changes. This study showed that bcl-2 mRNA was expressed in the theca and interstitial cells. Growing follicles of one or two days have showed stronger bcl-2 mRNA signals than atretic follicles of four or five days in these cells. Bax mRNA was expressed in the theca cells, interstitial cells, and granulosa cells. Atretic follicles of four or five days showed stronger bax mRNA signals than growing follicles of one or two days in these cells. Expression of bcl-2 mRNA was increased in growing follicles while decreased in atretic follicles. In contrast, expression of bax mRNA was increased in atretic follicles while decreased in growing follicles. Therefore, we confirmed that follicular development and atresia were affected by the change in the ratio of bcl-2 and bax mRNAs. According to these data, we proposed that these two genes are associated with follicular development and atresia.