Abstract
In vertebrates, sperm development and maturation are directly regulated by gonadal steroid hormone secretion. The relationships among the expression of genes encoding steroidogenic proteins and receptors for gonadotropins, and testicular steroid production have not yet been comprehensively determined in male teleosts. In this study, the changes in levels of mRNAs encoding follicle-stimulating hormone (FSH) receptor, luteinizing hormone (LH) receptor, steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side-chain cleavage, 3beta-hydroxysteroid dehydrogenase/delta5-4-isomerase, cytochrome P450 17alpha-hydroxylase/17,20-lyase, cytochrome P450 11beta-hydroxylase, 11beta-hydroxysteroid dehydrogenase and 20beta-hydroxysteroid dehydrogenase were determined by real-time, quantitative PCR assays and related to changes in serum steroid levels throughout the reproductive cycle in male rainbow trout. Serum 11-ketotestosterone and 17alpha,20beta-dihydroxy-4-pregnen-3-one levels were measured by RIA. Although the pattern of change in the mRNA levels for the enzymes was variable, the increases in steroidogenic enzyme mRNAs started prior to a significant increase of serum steroid levels. The patterns of transcript levels of FSH and LH receptors suggest that changes in StAR and steroidogenic enzyme transcripts are largely mediated by the FSH receptor during early and mid-spermatogenesis and by the LH receptor during late spermatogenesis and spermiation. Levels of StAR (10-fold) and P450 17alpha-hydroxylase/17,20-lyase (sevenfold) transcripts changed with the greatest magnitude and were closely related to the changes in serum steroids, suggesting that changes in StAR and P450 17alpha-hydroxylase/17,20-lyase abundance are likely to be the major influences on overall steroidogenic output during the reproductive cycle in male rainbow trout.
Highlights
In vertebrates, two types of gonadotropins (GTHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and gonadal steroid hormones have major roles in the regulation of spermatogenesis and sperm maturation
FSH in plasma was elevated during mid-spermatogenesis, whereas LH showed a significant increase in plasma during the spermiating stage (Prat et al 1996, Gomez et al 1999)
The aim of this study was to determine the changes in expression of the gene encoding steroidogenic enzymes and steroidogenic acute regulatory protein (StAR) in rainbow trout testes during spermatogenesis in relation to androgens and 17,20 -P production, and to changes in mRNAs encoding FSH receptor (FSH-R) and LH receptor (LH-R)
Summary
Two types of gonadotropins (GTHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and gonadal steroid hormones have major roles in the regulation of spermatogenesis and sperm maturation. FSH and LH primarily regulate steroid production through control of steroidogenic enzyme gene expression (Richards 1994). Binding of FSH or LH to their specific cell-surface receptors leads to the production of second messenger molecules which initiate changes in expression and activity of key steroidogenic enzymes for the synthesis of specific steroid hormones at specific times. Two distinct pituitary GTHs, GTH I and GTH II, were first isolated from chum salmon (Suzuki et al 1988) and coho salmon (Swanson et al 1991). Later studies demonstrated that GTH I and GTH II are structurally and functionally similar to FSH and LH, and GTH I and GTH II are currently recognized as FSH and LH respectively (Swanson et al 1989, Van der Kraak et al 1992, Koide et al 1993, Tanaka et al 1993, Okada et al 1994, García-Hernández et al 1997, Weltzien et al 2003). For salmon testis in vitro, the relative potencies of FSH and LH
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