Molecular cloning and expression of the duplicated thyroid hormone responsive spot 14 (THRSP) genes in ducks

Thyroid hormone responsive Spot 14 (THRSP) is suggested as a transcription factor involved in the regulation of adipogenic enzymes by 3 thyroid response elements in the promoter region. In the chicken genome, THRSP gene was identified to duplicate into 2 paralogs, THRSPalpha and THRSPbeta. In the current study, cDNA sequences of the duplicated duck THRSP genes were cloned by real-time PCR and rapid amplification of cDNA ends. Duck THRSPalpha and THRSPbeta were predicted to encode peptides with 133 amino acids, which had 74 and 68% sequence identity at cDNA level, 78 and 74% identity at amino acid level to the chicken counterparts, respectively. A high percentage (73.1%) of G and C nucleotides were found in the 3' untranslated region of duck THRSPbeta cDNA. Although a low similarity of peptide composition was shared between ducks and mammals, and a moderate similarity was shared between ducks and chickens, many predicted properties of THRSP, including the pI, subcellular localization and functional domains seemed to be highly conserved. The present study demonstrated that the duck THRSP gene duplicates into the 2 paralogs as in chickens. Phylogenetic analysis indicated that the duplication for THRSP paralogs appeared to have taken place preceding the chicken-duck split, and the diverging rate between THRSP paralogs seemed faster in the chicken genome than that in the duck genome. Expression analysis by real-time quantitative PCR showed that THRSP paralogs in ducks were more actively transcribed in fat tissues (i.e., s.c. fat and abdominal fat) than in liver, and the mRNA concentrations of THRSPbeta were higher than that of THRSPalpha in liver and s.c. fat.