Changes in plasma steroid levels and gene expression of pituitary gonadotropins, testicular steroidogenesis-related proteins and insulin-like growth factors during spermatogenesis of the yellowtail Seriola quinqueradiata

Abstract

We have examined the annual cycle of spermatogenesis in captive yellowtail Seriola quinqueradiata, including the associated changes in both plasma 11-ketotestosterone (11-KT) level and gene expression of key endocrine factors, such as the pituitary gonadotropin subunits, testicular steroidogenesis-related proteins and insulin-like growth factors (IGFs), at different testicular developmental stages. Spermatogenesis was initiated in January, and all males had progressed to the spermiation stage in April. Plasma 11-KT levels and gene expression profiles were analyzed in relation to changes in histological findings. Plasma 11-KT levels increased during early to late spermatogenesis and were positively correlated with early mitotic divisions of spermatogonia leading to meiosis. The genes encoding the follicle stimulating hormone (FSH) beta subunit (fshb) and the luteinizing hormone (LH) beta subunit (lhb) both showed parallel expression patterns during spermatogenesis. A previous study revealed that FSH receptor mRNA in yellowtail testes is strongly expressed from early to late spermatogenesis, whereas levels of LH receptor mRNA peak during spermiation; only cyp17a1 [encoding cytochrome P450 17α-hydroxylase/C17-C20 lyase (P450c17)] transcript levels increased during early spermatogenesis. The expression patterns of the genes encoding testicular IGF-1 and -2 (igf-1 and igf-2) differed from each other. Altogether, early spermatogenesis was associated with the regulation of 11-KT, which was probably induced by FSH through stimulation of specific steroidogenic enzymes, such as P450c17, and spermiation was considered to be triggered by LH. In addition, IGF-1 and IGF-2 are individually involved in spermatogenesis via autocrine/paracrine mechanisms.