Effects of sex steroids on gonadotropin (FSH and LH) regulation in coho salmon (Oncorhynchus kisutch)

Abstract

The effect of steroid hormone treatment on coho salmon (Oncorhynchus kisutch) was examined. The cDNAs for coho salmon FSH and LH subunits were cloned and sequenced using reverse transcriptase PCR. Northern blot analysis revealed that a single transcript of 1 kb for each of these subunits was present in the pituitaries of vitellogenic and spermiating coho salmon. RNase protection assays (RPAs) were developed to quantify FSH and LH subunit transcript levels. For the RPAs, antisense RNA probes and sense RNA standards were prepared from a region of the cDNAs which spanned the signal peptide and a portion of the mature protein. These RPAs were used to examine the effects of exogenous steroids including testosterone, estradiol-17 (E2) and 17 ,20 -dihydroxy-4-pregnen-3-one (17 ,20 -P) in vivo, in coho salmon at three time points during the spring period of gonadal growth when plasma levels of FSH are increasing. Both testosterone and E2 increased steady state mRNA levels of LH , whereas E2 decreased steady state mRNA levels of FSH in one experiment. Thus, the RPAs were able to detect changes in steady state mRNA levels in response to exogenous steroid treatment. Plasma and pituitary levels of FSH and LH were also measured using RIA. Throughout the experimental series, FSH plasma levels decreased in response to exogenous testosterone and E2 administration, while 17 , 20 -P had no effect on FSH plasma levels. Plasma LH levels were not detected throughout the course of the experiment. Pituitary LH increased in response to testosterone and E2, while pituitary FSH levels did not change. 17 ,20 -P had no effect on pituitary FSH or LH content during the experiment. Thus, regulation of the gonadotropins in coho salmon occurs at both the transcriptional as well as the translational level. Testosterone and E2 appear to have negative feedback effects on FSH, but positive feedback on LH.

Evidence for the existence of a local activin–follistatin negative feedback loop in the goldfish pituitary and its regulation by activin and gonadal steroids

“…Similar to those in mammals (Gharib et al 1990, Burger et al 2004, the secretion and expression of fish gonadotropins are controlled by both neuroendocrine factors from the hypothalamus such as gonadotropin-releasing hormone (GnRH; Peter et al 1986, Weltzien et al 2004, Ando & Urano 2005 and steroids from the gonads (Kobayashi et al 1987, Dickey & Swanson 1998. Our previous study in the goldfish demonstrated that in addition to the neuroendocrine and endocrine regulation, pituitary gonadotropins are also subject to local paracrine regulation by activin (Yam et al 1999a, Yuen & Ge 2004, similar to the situation in mammals (Roberts et al 1989, Corrigan et al 1991, Bilezikjian et al 2004.…”

Oestrogen-induced androgen insufficiency results in a reduction of proliferation and differentiation of spermatogonia in the zebrafish testis

“…Sex steroid, either androgens or oestrogens, feedback on gonadotropin synthesis and release is well established in fish (Dickey & Swanson 1998, Kobayashi et al 2001, Huggard-Nelson et al 2002, Banerjee & Khan 2008. In zebrafish, information on oestrogen effects on gonadotropin levels (either subunits mRNA expression levels or plasma levels) is scarce.…”

“…Previous studies have reported detrimental effects of oestrogenic compounds on fertility at all levels of the brainpituitary-gonad axis in teleost fish (Tsai et al 2005, Filby et al 2006, Zhang et al 2008, including impairment of spermatogenesis (Van der Ven et al 2003, Van den Belt et al 2004, Pawlowski et al 2004, and inhibition of androgen synthesis, either directly on Leydig cells (Loomis & Thomas 2000, Govoroun et al 2001, Baron et al 2005 or via feedback on hypothalamus and pituitary to control synthesis and release of gonadotropins (Dickey & Swanson 1998, Kobayashi et al 2001, Huggard-Nelson et al 2002, Banerjee & Khan 2008. However, it is not known exactly which step(s) in the developmental sequence constituting spermatogenesis is/are affected by oestrogens in fish.…”

Activity of the pituitary–gonadal axis is increased prior to the onset of spawning migration of chum salmon

“…In March and May, sGnRH, T or E2 elevated expression of the salmon fushi tarazu factor 1 homolog (sFF1-I) gene and estrogen receptor (ER) α, which directly activated the salmon LHβ promoter (Le Drean et al, 1996), in primary pituitary cells of masu salmon . Furthermore, T and E2 elevated the amounts of LHβ mRNA in primary pituitary cells of immature rainbow trout (Xiong et al, 1994), maturing coho salmon in February and April (Dickey and Swanson, 1998), and maturing masu salmon in May . Such stimulatory effects of sex steroids were attenuated after the late stages of gametogenesis in late July (Xiong et al, 1994;Ando et al, 2004;Onuma et al, 2007).…”