Androgen receptor-beta mRNA levels in different tissues in breeding and post-breeding male and female sticklebacks, Gast
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RESEARCH
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Androgen receptor-beta mRNA levels in different tissues in breeding and post-breeding male and female sticklebacks, Gasterosteus aculeatus Erik Hoffmann1, Anders Walstad2, Johnny Karlsson2, Per-Erik Olsson2 and Bertil Borg1*
Abstract Background: Androgens induce male characters by activating androgen receptors (AR). Previous quantitative studies on AR in fishes have been limited to few tissues and/or a single season/reproductive state. The aim of this investigation was to study the possible role of AR-beta expression levels in the control of male traits in the threespined stickleback. To that end, AR-beta expression levels in major tissues in breeding and post-breeding male and female sticklebacks were examined. Methods: AR-beta mRNA levels were quantified in ten tissues; eye, liver, axial muscle, heart, brain, intestine, ovary, testis, kidney and pectoral muscle in six breeding and post-breeding males and females using reverse transcription quantitative PCR. Results: Breeding in contrast to post-breeding males built nests and showed secondary sexual characters (e.g. kidney hypertrophy) and elevated androgen levels. Post-breeding females had lower ovarian weights and testosterone levels than breeding females. AR-beta was expressed in all studied tissues in both sexes and reproductive states with the highest expression in the gonads and in the kidneys. The kidney is an androgen target organ in sticklebacks, from which breeding males produce the protein spiggin, which is used in nestbuilding. There was also high AR-beta expression in the intestine, an organ that appears to take over hyperosmoregulation in fresh water when the kidney hypertrophies in mature males and largely loses this function. The only tissue that showed effects of sex or reproductive state on AR-beta mRNA levels was the kidneys, where postbreeding males displayed higher AR-beta mRNA levels than breeding males. Conclusion: The results indicate that changes in AR-beta mRNA levels play no or little role in changes in androgen dependent traits in the male stickleback.
Background Androgens stimulate masculine traits such as development of male secondary sexual characters, male reproductive behaviour and spermatogenesis via interactions with nuclear androgen receptors (AR). Among teleost fishes, complete AR cDNAs have been cloned in e.g. Japanese eel, Anguilla japonica [1], rainbow trout, Oncorhynchus mykiss [2] and red seabream, Pagrus major [3]. In some teleost fishes, two different AR genes have been cloned e.g. Japanese eel [1], Burton’s mouthbrooder, Astatotilapia burtoni [4] and Western mosquitofish, * Correspondence: [email protected] 1 Department of Zoology, Stockholm University, S-106 91 Stockholm, Sweden Full list of author information is available at the end of the article
Gambusia affinis [5]. The nomenclatur used for AR subdivision into alpha and beta is based on the first report of two forms present in Japanese eel [6]. We base the nomenclature in the present study on available phylogenetic analyses [6,7],
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