gonadectomy-blood-sampling-procedures-small-size-teleost-model

Gonadectomy and Blood Sampling Procedures in the Small Size Teleost Model Japanese Medaka (<em>Oryzias latipes</em>)

Sex steroids, produced by the gonads, play an essential role in brain and pituitary tissue plasticity and in the neuroendocrine control of reproduction in ...

The University of Tokyo

the university of tokyo

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.

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

It is widely known that reproduction in vertebrates is regulated by the hypothalamus-pituitary-gonadal (HPG) axis. Although the mechanism of the HPG axis has been well documented in mammals, it cannot be always applied to that in non-mammalian species, which is a great disadvantage in understanding reproduction of vertebrates in general. Recently, transgenic and genome editing tools have rapidly been developed in small teleosts, and thus these species are expected to be useful for the understanding of general mechanism of reproduction in vertebrates. One of the major sex steroid hormones in female vertebrates 17β-Estradiol (E2) plays crucial roles in the formation of sexual dimorphism and the HPG axis regulation. In spite of the importance of E2 in reproductive regulation, only a few studies have analyzed blood E2 levels in small teleosts that are easily amenable to genetic manipulation. In the present study, we analyzed blood E2 concentration in medaka and demonstrated that female medaka show diurnal changes in blood E2 concentration. We then examined the best method for manipulating the circulating E2. First, we found that ovariectomy (OVX) drastically removes endogenous E2 in a day in female medaka. We examined different methods for E2 administration and revealed that feeding administration of E2-containing food is the most convenient and physiological method for mimicking the diurnal E2 changes of female medaka. On the other hand, the medaka exposed to E2 containing water showed high blood E2 concentrations, which exceeds those of environmental water, suggesting that E2 may cause bioconcentration.

Article	Year
Gene knockout analysis reveals essentiality of estrogen receptor β1 (Esr2a) for female reproduction in medaka. Scientific reports\| PubMed ID: 31222039	2019
Examination of methods for manipulating serum 17β-Estradiol (E2) levels by analysis of blood E2 concentration in medaka (Oryzias latipes). General and comparative endocrinology\| PubMed ID: 31525376	2020

Daichi Kayo

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