Proliferation and apoptosis in follicles of the marmoset monkey (Callithrix jacchus) ovary

Abstract

Proliferation and apoptosis were studied in ovarian follicles of immature and pubertal marmosets and in mature marmosets during the follicular, periovulatory and luteal phases. Proliferation was evaluated using a Ki 67 antibody and apoptosis was assessed by in situ detection of DNA fragmentation. In the immature animals only small follicles were present, and the expression of Ki 67 was restricted to the granulosa cells of follicles localised near the medulla. There was no evidence of DNA fragmentation. In pubertal and adult animals Ki 67 expression was found in the granulosa cells of some but not all primordial and primary follicles. In the secondary and tertiary follicles immunoreactivity was localized in theca cells and granulosa cells. In atretic follicles (morphologically classified) the number of Ki 67 positive granulosa cells varied. In corpora lutea as well as in corpora lutea accessoria, staining was seen in the nuclei of some luteal cells. During all phases of the cycle, follicles from the secondary stage onwards were proliferating, whereas granulosa cells of primary follicles were only stained during the follicular phase. During all phases of the ovarian cycle apoptosis was restricted to the granulosa cells of tertiary follicles. With regard to proliferation and apoptosis, follicles exhibiting morphological signs of atresia can be classified as follows: (1) granulosa cells showing strong Ki 67 expression; (2) granulosa cells with reduced expression of Ki 67; (3) granulosa cells devoid of Ki 67 immunoreactivity and of apoptotic signs; (4) granulosa cells heavily stained for DNA fragmentation and not stained for Ki 67; (5) granulosa cells close to the antrum showing DNA fragmentation but luteinizing Ki 67 positive granulosa cells close to the basement membrane. In summary, it was shown that atresia of tertiary follicles is characterised by three consecutive stages: morphological alterations, cessation of proliferation and finally apoptosis in tertiary follicles. Thus, our results indicate that early atresia as evidenced by the morphological signs is not necessarily related to DNA fragmentation, since apoptosis is exclusively found in the granulosa cells of advanced atretic tertiary follicles.