Gene expression profiling during spermatogenesis in early maturing male Atlantic salmon parr testes Gersende Maugars a , Monika Schmitz b, * a Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden b Department of Biology, Karlstad University, Universitetsgatan 2, SE-651 88 Karlstad, Sweden article info Article history: Received 14 April 2008 Revised 21 July 2008 Accepted 19 August 2008 Available online 28 August 2008 Keywords: Puberty Spermatogenesis Male Atlantic salmon parr Steroidogenic enzymes StAR Ff1b AMH abstract The initiation of sexual maturation and spermatogenesis are complex processes that require the highly coordinated regulation of a number of key genes. The endocrine system plays crucial roles in these processes, but the precise mechanisms involved in sexual maturation of fish are poorly understood. We investigated the expression of genes encoding proteins involved in sex steroid biosynthesis (Ff1b (FTZ-F1 homolog), steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), 3b-hydroxysteroid dehydrogenase/D 5 –D 4 –isomerase (3b-HSD), cytochrome P450 17a-hydroxylase/17,20-lyase (P450c17), cytochrome P450 11b-hydroxylase (P45011b) and 11b-hydroxysteroid dehydrogenase (11b-HSD)) and the anti-Müllerian hormone (AMH) homolog during early sexual maturation of one-summer-old male Atlantic salmon parr by RT-PCR. Genes encoding Ff1b, StAR, 3b-HSD, P450c17 and 11b-HSD were upregulated during spermatogonial proliferation. During the course of spermatogenesis expression profiles of Ff1b, StAR, 3b-HSD, P450scc, P450c17, P45011b, and 11b-HSD were similar; transcript levels being low during early stages, then strongly increasing during spermiogenesis. These results indicate that coordinated de novo transcription of genes encoding StAR as well as 3b-HSD, P450c17 and 11b-HSD might be required for sex steroids production during the initi- ation of spermatogenesis in salmon. In contrast, transcription levels of AMH were comparatively high in immature testes, decreased when spermatogenesis was initiated, and were lowest during spermiogene- sis, suggesting that AMH suppression plays a crucial role in the process of spermatogenesis in salmonids. Correlation analyses show that FSH and LH might be differentially involved in the regulation of several of these genes studied. Ó 2008 Elsevier Inc. All rights reserved. 1. Introduction The initiation of sexual maturation in male teleost fish is char- acterized by the onset of spermatogenesis (Schulz and Miura, 2002). Spermatogenesis is a complex process that starts with the mitotic proliferation of spermatogonia, followed by meiosis, and concludes with the transformation of haploid spermatids into mature functional spermatozoa. Reproductive functions in teleosts are regulated by the brain–pituitary–gonad axis. In salmonids the initiation of spermatogenesis is characterized by an increase of the expression and release of FSH while plasma LH are undetect- able or very low until early gametogenesis then rise considerably at the spermiogenesis–spermiation (for review see Yaron et al., 2003). FSH and LH act via the stimulation of two specific G pro- tein-coupled receptors in the gonads (Yan et al., 1992; Miwa et al., 1994). CDNA encoding FSH receptor (FSHR) and LH receptor (LHR) have been recently isolated in Atlantic salmon (Salmo salar) (Maugars and Schmitz, 2006). Transcripts encoding both gonado- tropin receptors are expressed in immature salmon testes, FSHR transcripts more abundantly than LHR transcripts (Maugars and Schmitz, 2008). During spermatogenesis, FSHR transcript levels increase in parallel to FSHb levels from early spermatogenesis onwards, while LHR mRNA start to increase prior to any major changes in LHb levels. In salmonids, FSH and LH equipotentially stimulate the production of the androgens, 11-ketotestosterone (11-KT) and testosterone (T). However, LH is a more potent stimu- lant than FSH of 17a,20b-dihydroxy-4-pregnen-3-one (17a,20b-P) synthesis at final maturation and spawning in both males and females (Planas and Swanson, 1995). In male teleosts, T and especially 11-KT are considered the main androgens (Borg, 1994) and together with 17a,20b-P they play important roles in spermatogenesis. In eels and catfish, stimulation by 11-KT has been shown to activate all stages of spermatogenesis (Miura et al., 1991). However, in salmonids, the ability of 11-KT to induce spermatogenesis is less clear (Loir, 1999; Amer et al., 2001). The biosynthesis of 11-KT, T and 17a,20b-P requires the coordi- nated action of several steroidogenic enzymes. The cytochrome 0016-6480/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.ygcen.2008.08.008 * Corresponding author. Fax: +46 54 700 1462. E-mail address: monika.schmitz@kau.se (M. Schmitz). General and Comparative Endocrinology 159 (2008) 178–187 Contents lists available at ScienceDirect General and Comparative Endocrinology journal homepage: www.elsevier.com/locate/ygcen