Cloning, sequence analysis, and expression of tyrp1a and tyrp2 genes related to body colour in different developmental stages and tissues of rainbow trout Oncorhynchus mykiss

Abstract

Tyrosinase-related protein 1 (tyrp1) and tyrosinase-related protein 2 (tyrp2) genes are important downstream regulatory factors for body colour formation in animals. The present study aimed to explore the relationship between tyrp1a and tyrp2 expression and body colour variation between wild-type (WT) and yellow mutant (YM) rainbow trout. The full-length cDNA sequences of trout tyrp1a and tyrp2 were obtained using rapid amplification of cDNA ends, and the bioinformatic analysis was performed. Quantitative real-time PCR (qRT-PCR) was used to investigate the different expression levels of tyrp1a and tyrp2 in different developmental stages and tissues. The full-length cDNAs of tyrp1a and tyrp2 were 2409 bp and 2219 bp encoding predicted proteins of 522 and 529 amino acid residues, respectively. Both proteins possess six conserved domains, including a signal peptide, an EGF-motif, a Pfam tyrosinase motif, a transmembrane structure, and two copper binding sites (CuA and CuB). Amino acid sequence comparisons showed higher conservation of Tyrp1a and Tyrp2 proteins amongst fishes than amongst other vertebrates, which was further confirmed by phylogenetic analysis. qRT-PCR analysis revealed that tyrp1a and tyrp2 expression levels in WT rainbow trout, and tyrpla in YM rainbow trout, were detected from the fertilised stage to 12 months post hatching (12 M), while tyrp1a did not expressed until the blastula in YM rainbow trout. In addition, the expression levels of both of the genes post hatching were significantly higher than those in the embryonic stages, which showed extremely low expression levels. Additionally, there were extremely significant differences (P < 0.01) in expression at the same stages between WT and YM rainbow trout, e.g., at the blastula, gastrula, 7 days post hatching (7 dph), 10 dph, 2 M, 3 M, 6 M, and 12 M stages for tyrp1a; and at the 4-cell, 16-cell, multicell, blastula, somites, heartbeating, 1 dph, 5 dph, 7 dph, 3 M, 6 M, and 12 M stages for tyrp2. Besides, variable expression levels of tyrp1a and tyrp2 were detected in all tissues; significantly high expression was detected in the dorsal skin and eye compared with that in the other tissues in WT and YM rainbow trout (P < 0.05). These results suggested that the expression level changes of tyrp1a and tyrp2 might be closely related to the variation of rainbow trout body colour, which will enrich our knowledge of the molecular mechanism of skin colour variation in rainbow trout and provide data for research into fish skin colour inheritance and improvement.