Regulation of prostaglandin synthesis in the zebrafish ovary

Abstract

Oocyte maturation and ovulation are two major events that occur in fish prior to spawning. While earlier studies have shown that 17α, 20β-dihydroxy-4-pregnen-3-one (17,20β-P) and the insulin-like growth factor (IGF) system are regulators of oocyte maturation in the zebrafish (Danio rerio), it is not known whether these hormones play a role in regulating prostaglandin synthesis which is thought to mediate ovulation. I determined if 17,20β-P and human IGF-1 affect the expression of genes involved in prostaglandin biosynthesis including phospholipase A2 (cpla2) and cyclooxygenase-1/2 (ptgs1/ptgs2), or prostaglandin F2α (PGF2α) levels. 17,20β-P and IGF-1 stimulated oocyte maturation in mid-vitellogenic (MV) and full grown (FG) follicles. In FG follicles, 17,20β-P increased cpla2 expression, whereas IGF-1 increased cpla2 and ptgs2 expression. Both 17,20β-P and IGF-1 increased PGF2α production. The phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signalling pathways were shown to mediate IGF-1- and 17,20β-P-induced oocyte maturation and cpla2 and ptgs2 expression. Collectively, these results demonstrate that 17,20β-P and IGFs are important regulators of oocyte maturation and prostaglandin synthesis in zebrafish.