Abstract：Tyrosinase (TYR) is the one of the most important rate-limiting enzymes in animals within the signal path of melanin synthesis, which plays a crucial role in the formation of melanin. So the expression and activity level decide the speed and type of melanin. This study was conducted to reveal the relationship between genes related to pigment and body color. We obtained tyrosinase gene (TYR) sequence of Amphilophus citrinellus by rapid-amplification of cDNA ends (RACE) technique and also investigated the expression of TYR in different developmental stages and tissues using qRT-PCR. The total length of TYR was 2 683 bp which contained 246 bp 5'-UTR, 817 bp 3'-UTR, and 1 620 bp open reading frame (ORF) encoding 540 amino acids in A. citrinellus. Sequence analysis of amino acids and phylogenetic tree analysis indicated that conservation of TYR was higher in fish than that in other vertebrates. qRT-PCR analysis revealed that TYR expressed in embryonic periods was lower in the conception and began to sharply rise in the circulation of the blood period. In the process of body color changes (black to gray to bright yellow), the expression of the TYR in black period of all tissues was significantly higher than that in grey and bright yellow period (P＜0.05). TYR expression of tail fin and scale was gradually reduced in gray to bright yellow period, while there is no significant difference between these two periods (P＞0.05). However, expression of TYR in skin significantly decreased during the body color developmental stages (P＜0.05). In the bright yellow period, TYR expressed in all kinds of tissues (heart, kidney, brain, maw, gonad, tail fin and eye), which expressed the highest amount in eyes, intermediate in swim bladder and tail fin and the lowest in skin and glands. Also, TYR expression gradually decreased among three periods of body color development. It may be related to the gradual increase of red and yellow pigment cells, as well as the changes of the number and distribution proportion of melanocytes. This study accumulated data for body color genetic and modified research of the body color in fish by revealing the molecular basis of body color variations.
