Gene knockout analysis reveals essentiality of estrogen receptor β1 (Esr2a) for female reproduction in medaka

Abstract

In vertebrates, sex steroids play crucial roles in multiple systems related to reproduction. In females, estrogens and their receptor estrogen receptor (ER or Esr) play indispensable roles in the negative sex steroid feedback regulation of pituitary gonadotropin secretion, which prevents excessive development of ovarian follicles. However, the mechanism of this feedback regulation of a gonadotropin, follicle stimulating hormone (FSH), which is essential for folliculogenesis throughout vertebrates, is poorly understood. In the present study, we generated knockouts of all subtypes of nuclear estrogen receptors in a model teleost medaka, which is suitable for the study of endocrine control and behavioral assays, and analyzed fertility, behavior and functionality of estrogen feedback in each knockout line. Among the estrogen receptors, we revealed that an estrogen receptor Esr2a plays an essential role in this feedback regulation. In addition to this, we also found that esr2a −/− females showed oviduct atresia, which causes complete infertility. Interestingly, esr2a −/− females showed apparently normal sexual behavior but without oviposition in response to male courtship. This phenotype indicates that physical readiness and motivation of sexual behavior is independently controlled.

Plasticity in medaka gonadotropes via cell proliferation and phenotypic conversion

“…Journal of Endocrinology (Kominami et al 2003) including gonadotropes themselves (Childs & Unabia 2001). Sex steroids play crucial roles in multiple systems related to reproduction, and E2 has been shown to play an essential role in medaka reproduction (Kayo et al 2019). While the number of Fsh cells as well as Lh cells labelled by BrdU increased after E2 or testosterone treatment in males, this was not the case following treatment with 11-KT (a non-aromatizable androgen).…”

Distribution of aromatase in the brain of the African cichlid fish Astatotilapia burtoni: Aromatase expression, but not estrogen receptors, varies with female reproductive‐state

“…Brain aromatase is abundant along ventricular surfaces in fishes, and primarily expressed in radial glial cells rather than in neurons as seen in birds and mammals (Balthazart et al, 2006;Forlano, Deitcher, Myers, & Bass, 2001;Forlano et al, 2006). Further, aromatase and estrogen receptors in the female brain are implicated in the control of ovarian readiness, as well as reproductive motivation and expression of behaviors (Diotel et al, 2010;Kayo, Zempo, Tomihara, Oka, & Kanda, 2019). Teleosts also display remarkable sexual plasticity throughout their lifetime, including sex-steroid modulation of sex-specific social behaviors after sexual maturity, making them excellent models to investigate neural mechanisms of activational hormone-modulated biological processes.…”

Gonadectomy and blood sampling procedures in small size teleost models

“…As documented in previous studies with different animal models, the protocol described here will allow us to investigate questions related to reproductive physiology using small teleosts as model. In fact, these techniques have already contributed to answer questions concerning the regulation of the BPG axis and its feedback mechanisms, such as the involvement of kiss1 (kisspeptin gene type 1) expressing neurons in positive feedback loops 54 , estrogen-mediated regulation of kiss1 expressing neurons in nucleus ventralis tuberis (NVT), and kiss2 (kisspeptin gene type 2) expressing neurons in preoptic area (POA) 55,56 , the expression profile of fshb (follicle-stimulating hormone beta sub-unit gene) in esr2a (estrogen receptor gene) knock out (KO) fish 57 as well as the profile of circadian rhythm of E2 in female fish 53 . Furthermore, since previous studies demonstrated that sex steroids also affect the proliferation of gonadotropic cells in the pituitary of teleosts 58,59 , it would be intriguing to investigate the effects of sex steroid clearance after gonadectomy on pituitary plasticity.…”