Differential expression of Atlantic salmon thyrotropin beta subunit mRNA and its cDNA sequence

To study the regulation of the thyroid system, an Atlantic salmon Salmo salar cDNA clone was isolated for thyroid stimulating hormone (TSH) beta subunit gene. A cDNA (866 bp) was isolated from an adult Atlantic salmon pituitary cDNA library, this clone was sequenced and shown to be highly conserved when compared to other teleost beta TSH subunit sequences. The cDNA was used as a probe for Northern blot analysis of total pituitary RNA from the different life cycle stages of Atlantic salmon. Northern blot analysis demonstrated that beta TSH mRNA is expressed at all life cycle stages studied, including parr, smelt, immature fish at sea and sexually mature male fish. Densitometry of Northern blots showed that sexually mature male salmon had low levels of salmon beta TSH mRNA compared to non-mature fish. Stunts, fish performing poorly in salt water, were shown to have elevated levels of beta TSH mRNA when compared to healthy fish. (C) 1999 The Fisheries Society of the British Isles.