The Testis Is a Primary Factor That Contributes to Epigenetic Modifications in the Ovaries of the Protandrous Black Porgy, Acanthopagrus schlegelii

Abstract

In most hermaphroditic fish, the sexual phase of the gonad responds to external stimuli so that only one sex remains functional while the other sex becomes dormant. However, protandrous black porgy are male during their first two reproductive cycles. Estradiol (E2)-induced female growth results in a transient and immature female, and the sexual phase reverts from female to male after E2 is withdrawn. Conversely, excising the testis results in a precocious female when performed during the second reproductive cycle. We used these characteristics to study epigenetic modifications of cyp19a1a promoter in black porgy. Our results showed that higher levels of gonadotropins receptors were observed in testis than in ovary during the alteration of sexual phase from induced femaleness to maleness, and hCG treatment did not stimulate ovarian gene expression in male (1-yr-old maleness) and female phase (testis excision-induced femaleness) fish. The cyp19a1a promoter exhibited tissue- and lineage-specific methylation patterns. The follicle cells in the ovary had a hypomethylated (0%-20%) cyp19a1a promoter region. In the ovary, the first sign of female phase decision was decreased methylation levels and increased numbers of hypomethylated clones of cyp19a1a promoter during the natural sex change process. Similar methylation patterns were observed in the testis-removed ovary 1 mo after surgery, with no histological difference between the sham and the testis-removed fish. Conversely, there was no increase in methylation levels of cyp19a1a promoter in E2-fed fish. These results suggest that in the digonic gonad of black porgy, the testis is the primary tissue that affects epigenetics of the ovary.

Keywords: cyp19a1a; hermaphroditic fish; methylation; ovary; sex change; testis.