Molecular cloning of cDNA encoding thyroid stimulating hormone beta subunit of bighead carp Aristichthys nobilis and regulation of its gene expression

The complementary DNA (cDNA) encoding pituitary thyroid stimulating hormone beta subunit (TSH-beta) of bighead carp was cloned and regulation of its g ene expression was investigated for understanding phylogenetic divergence a nd evolution of TSH molecule. The cDNA was obtained from bighead carp pitui tary total RNA by reverse transcription and polymerase chain reaction. Olig onucleotide primers were designed from the sequence of common carp. The ful l length sequence was then obtained by 3' and 5' rapid amplification of cDN A ends (RACE). The full-length sequence consisting of 3' and 5' untranslate d regions was 585 bp long. The predicted amino acid sequence consisted of a signal peptide of 19 amino acid residues and a mature TSH beta subunit pro tein of 131 residues. The coding sequences of the cDNAs showed variable per centage homologies with those of other teleosts and vertebrate species. The predicted amino acid sequence shared 71% identity with rainbow trout and s almon, 90% with goldfish, 50%, with eel anti 94% with common carp in the ma ture protein region. The percentages of identity in the same region in comp arison with bovine, porcine, rat, mouse, human and chicken were only 39, 42 , 41, 40, 45 and 46%, respectively. TSH beta mRNA expression was found only in the pituitary tissue out of other tissues tested as testis, muscle; bra in and heart. For the first time, thyrotropin releasing hormone (TRH) and t hyroxine (T-4) effects on pituitary TSH mRNA expression were tested in tele osts under in vitro conditions. TRH treatment on pituitary cells increased TSH beta mRNA level, while T-4 treatment decreased TSH beta mRNA level. The present study provides a direct evidence, for the first time that TRH dire ctly upregulates TSH beta gene expression in teleosts. (C) 2001 Elsevier Sc ience Ireland Ltd. All rights reserved.