PCNA in the ovary of zebrafish (Brachydanio rerio, Ham.-Buch.).

PCNA, a nuclear protein intimately involved in DNA synthesis, has been localized immunohistochemically in ovaries of zebrafish (Brachydanio rerio, Ham.-Buch.). Positively stained cells were detected in the follicle epithelium of all stages of growing oocytes and degenerating oocytes. Furthermore, PCNA was found to be present in nuclei of oogonia and oocytes in meiotic prophase. Follicle epithelium showed an increasing number of PCNA-positive cells during egg cell development with a very low index of <0.5% at the beginning and a maximum of >7% in stage IV oocytes that are rapidly incorporating yolk protein. In this phase, follicle epithelium often showed groups of stained cells in limited zones of proliferation. In degenerating oocytes, over 60% of the former follicle cells were positive for PCNA. Nuclei of oogonia were always positive and the nucleus of stage III oocytes showed strong positivity. Stage III is the stage in which amplification of rRNA genes occurs and numerous nucleoli apear in the peripheral caryoplasm. It is concluded that PCNA expression is related to amplification of rDNA.