PCNA and apoptosis during post-spawning ovarian remodeling in the teleost Oreochromis niloticus

The balance between cell proliferation and apoptosis is crucial for tissue development and homeostasis. The present study investigated the contribution of proliferating cell nuclear antigen (PCNA) and apoptosis during ovarian remodeling after spawning in the Nile tilapia Oreochromis niloticus. Breeding females were kept in controlled conditions and ovary samples were collected weekly for TUNEL assay, immunohistochemistry for PCNA and caspase-3 and morphometric analysis. During the follicular growth, PCNA labeled mainly the nuclei of oocytes and follicular cells in a high proportion of follicles especially in primary growth, while a low occurrence of apoptosis in follicular and theca cells was detected. At 0-3 days post-spawning, post-ovulatory follicles showed no proliferative activity, however the follicular cells exhibited high rates of apoptosis. At 7-10 days, PCNA labeled the thecal cells in a low proportion of post-ovulatory follicles, which showed follicular cells with lower rates of apoptosis. PCNA labeled mainly the theca in the advanced and late stages of atretic follicles, while the follicular cells exhibited a significant increase of apoptosis along follicular atresia. We concluded that PCNA and apoptosis work cooperatively to ensuring the success of follicle development and maintaining of tissue homeostasis during follicular growth. PCNA and apoptosis are also essential mechanisms in the follicular regression during post-spawning ovarian recovery in the Nile tilapia.