Selection pressure analysis of tyrosinase (TYR) gene in Oujiang color common carp (Cyprinus carpio var. color)

Abstract:

Tyrosinase (TYR) is a key and rate-limited enzyme in melanin synthesis pathway. Black spots are one of the main body color characteristics in Oujiang color common carp (Cyprinus carpio var. color). In this study, the total of the fifth generations of Oujiang color common carp (F₅) were used to observe the variation and selective pressure sensitivity of tyrosinase (TYR) gene among the five exons in this gene and among the five body color patterns in this fish. The results showed: the nucleotide variation rate and the number of their positive selection sites in exon 1 and exon 5 were higher than those of the other three exons, indicating these two exons were more easily subjected to selective pressure. The ratios (ω) of d_N/d_S of the five exons were all less than 1 (0.10-0.67), which demonstrated there was purifying selection conducted in tyrosinase gene. Similarly, the ratio (ω=0.12-0.23) illustrated there was also purifying selection in the five body color patterns of Oujiang color common carp. The amino acid site analysis of selection pressure using the Codeml models (M2a and M8) in the software PAML indicated that there were more positive selection sites in the fish without black spots than the fish with black spots, although there was no significant difference (P>0.05). Furthermore, some amino acid sites were also found with more easily positive selection than the other acids in tyrosinase gene. Generally, tyrosinase gene was conservative in evolutionary process and mainly subjected to purifying selection in Oujiang color common carp, and no significant selection pressure on this gene was found under artificial selection in this fish.