Romano, S. N. | Search bioRxiv

bioRxiv2018

G protein-coupled estrogen receptor is not required for sex determination or ovary function in zebrafish

Estrogens regulate vertebrate development and function through binding to nuclear estrogen receptors alpha and beta (ER, ER{beta}) and the G protein-coupled estrogen receptor (GPER). Studies in mutant animal models demonstrated that ER and ER{beta} are required for normal ovary development and function. However, the degree to which GPER signaling contributes to ovary development and function is less well understood. Previous studies using cultured fish oocytes found that estradiol inhibits oocyte maturation in a GPER-dependent manner, but whether GPER regulates oocyte maturation in vivo is not known. To test the hypothesis that GPER regulates oocyte maturation in vivo, we assayed ovary development and function in gper mutant zebrafish. We found that homozygous mutant gper embryos developed into male and female adults with normal sex ratios and fertility. Adult mutant fish exhibited normal secondary sex characteristics and fertility. Additionally, mutant ovaries were histologically normal. We observed no differences in the number of immature versus mature oocytes in mutant versus wild-type ovaries from both young and aged adults. Furthermore, expression of genes associated with sex determination and ovary function were normal in gper mutant ovaries compared to wild type. Our findings suggest that GPER is not required for sex determination, ovary development or fertility in zebrafish.

developmental biology↗

bioRxiv2016

G protein-coupled estrogen receptor regulates heart rate in zebrafish embryos

Estrogens act by binding to estrogen receptors alpha and beta (ER, ER{beta}), ligand-dependent transcription factors that play crucial roles in sex differentiation, tumor growth and cardiovascular physiology. Estrogens also activate the G protein-coupled estrogen receptor (GPER), however the function of GPER in vivo is less well understood. Here we find that GPER is required to maintain normal heart rate in zebrafish embryos. Acute exposure to estrogens increased heart rate in wildtype and in ER and ER{beta} mutant embryos but not in GPER mutants. Nuclear estrogen receptor signaling remained normal in GPER mutant embryos, however GPER mutant embryos exhibited reduced basal heart rate while heart rate was normal in ER and ER{beta} mutants. We detected GPER transcript in discrete regions of the brain but not in the heart. In the brain, we observed gper expression in cells lacking nuclear estrogen receptor activity, suggesting that GPER acts in the brain to regulate heart rate independently of nuclear estrogen receptor signaling. Our results demonstrate that estradiol plays a previously unappreciated role in the acute modulation of heart rate during zebrafish embryonic development and that GPER functions as an autonomous estrogen receptor in vivo to regulate basal heart rate.

pharmacology and toxicology↗