Reduced Vitellogenesis and Female Fertility in Gper Knockout Zebrafish

Abstract

The role G-protein coupled estrogen receptor (GPER) plays in vertebrate reproduction remains controversial. To investigate GPER's reproductive role, we generated a gper zebrafish mutant line (<i>gper^-/-</i> ) using TALENs. Gper mutant females exhibited reduced fertility with a 40.85% decrease in embryo production which was associated with a significant decrease in the number of Stage V (730-750 μm) ovulated oocytes. Correspondingly, the number of early vitellogenic follicles (Stage III, 400-450 µm) in <i>gper^-/-</i> ovaries was greater than that in wildtypes (<i>wt</i>), suggesting that subsequent follicle development was retarded in the <i>gper^-/-</i> fish. Moreover, plasma vitellogenin levels were decreased in <i>gper^-/-</i> females, and epidermal growth factor receptor (Egfr) expression was lower in Stage III vitellogenic oocytes than in <i>wt</i> counterparts. However, hepatic nuclear estrogen receptor levels were not altered, and estrogen levels were elevated in ovarian follicles. These results suggest that Gper is involved in the control of ovarian follicle development <i>via</i> regulation of vitellogenesis and Egfr expression in zebrafish.