Involvement of Estrogen and Its Receptors in Morphological Changes in the Eyes of the Japanese Eel, Anguilla japonica, in the Process of Artificially-Induced Maturation

Abstract

During the long migration from river habitats to the spawning ground, the Japanese eel undergoes sexual maturation. This spawning migration occurs concurrently with morphological changes, such as increases in eye size; however, the mechanisms by which sex steroids and their receptors influence these changes in peripheral tissues remain unclear. The aim of this study was to investigate changes in the eyes of female Japanese eels during sexual maturation, and our research focused on estrogen receptor (ER)α and ERβ transcripts. During ovarian development, the gonadosomatic index increased and yolk-laden oocytes developed rapidly. These changes occurred in conjunction with a steady increase in plasma levels of estradiol-17β (E2). Concomitant increases in transcript levels of ERα and ERβ in eye, brain, pituitary, and ovary were also observed. Fluorescence in-situ hybridization analyses revealed that ERα and ERβ transcripts were present in the choriocapillary layer and photoreceptor layer of the eyes, and the analysis also revealed that their signals in these layers became stronger in mature females compared to those observed in immature females, suggesting that under the influence of gonadotropins, morphological changes in the eyes are regulated by E2 through the activation of its receptors. In conclusion, E2 plays a crucial role in physiological adaptations that occur in peripheral tissues during the spawning migration.

Development of a Comprehensive Toxicity Pathway Model for 17α-Ethinylestradiol in Early Life Stage Fathead Minnows (Pimephales promelas)

“…EE2 has been implicated in disruptions in brain and nervous system-specific gene expression in medaka . While there were no reports in the literature showing direct effects of EE2 to visual development, the increase in plasma levels of 17β-estradiol, a closely related estrogen, was concomitant with the increase in ERα and ERβ transcripts in the choriocapillary layer and photoreceptor in artificially induced maturation of Japanese eel . Furthermore, it has been reported that estrogen signaling is involved in retinal development in developing embryos of zebrafish .…”

17β-Estradiol Modulates SIRT1 and Halts Oxidative Stress-Mediated Cognitive Impairment in a Male Aging Mouse Model

“…The steroid hormone 17β-estradiol is mainly synthesized by the enzyme aromatase in the ovary, as well as locally in tissues such as bone, adipose, and nerve tissues in both males and females. It has been reported that hippocampal neurons express E2-synthesizing enzyme P450 aromatase, which modulates synaptic function in vivo [28,29]. In recent decades, the brain has been considered as a “steroidogenic” organ because it expresses the molecules and enzymes that are required for the conversion of cholesterol into steroids such as progesterone, testosterone, and estradiol.…”

A Deep Insight of Spermatogenesis and Hormone Levels of Aqua-Cultured Turbot (Scophthalmus maximus)

“…An increasing evidence suggests that estrogens involve in both the spermatogenesis and the regulation of testicular functions (Schulz et al, 2010;Björn et al, 2013). Estrogen receptors have been identified in testis (Dumasia et al, 2016;Kumar et al, 2018), and they generally respond to the secretion of E2 differ between developmental stages of the gonads and different organs (Hyeon et al, 2019). However, estrogens in the testis are produced by Leydig cells, Sertoli cells, and germ cells through the aromatization of testosterone, and they are very active during puberty initiation (Amer et al, 2001;Takeshi and Chiemi, 2003) and spermatogenesis (Munakata and Kobayashi, 2010;Björn et al, 2013;Kumar et al, 2018).…”

“…In contrast, there are more reports of hormones during fish reproduction, including studies on sex steroids (e.g., androgen, estrogen, and progesterone) (Weltzien et al, 2002;Miura et al, 2006;Schulz et al, 2008Schulz et al, , 2010Björn et al, 2013;Chen et al, 2013;Hachero-Cruzado et al, 2013;O'Shaughnessy, 2014;Chauvigné et al, 2016Chauvigné et al, , 2017Hyeon et al, 2019), and other hormones [e.g., thyroid, and 5-hydroxytryptamine (5-HT)] (Bertil, 1994;Fallah-Rad et al, 2001;Holsberger et al, 2005;Mendis-Handagama and Siril Ariyaratne, 2005;Kreke and Dietrich, 2008;Wagner et al, 2008;Munakata and Kobayashi, 2010), which all involved in the spermatogenesis and the maintenance of male function. These works have provided us with ideal candidates in studying the regulation of steroid hormones during spermatogenesis.…”