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 (gper−/−) 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 gper−/− ovaries was greater than that in wildtypes (wt), suggesting that subsequent follicle development was retarded in the gper−/− fish. Moreover, plasma vitellogenin levels were decreased in gper−/− females, and epidermal growth factor receptor (Egfr) expression was lower in Stage III vitellogenic oocytes than in wt 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 via regulation of vitellogenesis and Egfr expression in zebrafish.
Highlights
Reduced Fertility in Gper KO [10,11,12]
In gper−/− mutant line, an eight-nucleotide deletion mutation was generated in exon 3 (Figure 1C) that caused a frameshift resulting in truncation of the transcript prior to the region encoding the first transmembrane domain of gper (Figure 1D)
The present results in zebrafish provide new evidence that G-protein coupled estrogen receptor (GPER) has a role in fertility via regulation of vitellogenesis and epidermal growth factor receptor (Egfr) in female zebrafish
Summary
Reduced Fertility in Gper KO [10,11,12]. Extensive studies have suggested the involvement of GPER in numerous estrogen-mediated physiological functions in mammals [8], including lipid metabolism and vascular function [13], insulin secretion [14], growth plate fusion [15], and reproductive functions such as primordial follicle formation in ovaries [16], as well as regulation of vitellogenesis [17] and oocyte meiotic arrest in fishes [7]. GPER has been implicated in estrogen-induced firing activity of calcium oscillations in luteinizing hormone releasing hormone (LHRH) neurons, in uterine proliferation and estrogeninduced augmentation of the oxytocin uterine contraction response, in the growth and proliferation of endometrial cells, apoptosis during spermatogenesis, and in breast, uterine, endometrial, and ovarian and testicular tumorigenesis [8, 12, 20, 22,23,24] Whether this estrogen receptor plays a role in mammalian reproduction is still controversial because a few GPER knockout studies conducted in mice have suggested that GPER is not critical for mammalian reproduction due to lack of an effect on fertility and oocyte development [14, 25,26,27,28]. Our results suggest that gper has roles in ovarian development and female fertility in zebrafish
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