Changes of pigment-related enzyme activity and gene expression at early developmental stage of koi carp

We investigated the changes of tyrosinase and cystinase activities, as well as the expressions of tyr, mitf, agouti and mc1r mRNAs at the early developmental stage of Kohaku and Hi-Utsuri koi carp (Cyprinus carpio) by using histological observation, enzyme-linked immunoassay and quantitative reverse transcription-polymerase chain reaction methods. The results show that the hatched carps became light yellow and translucent. The melanocytes occurred on 8 dph (day-post-hatching). The activity of cystinase increased with the koi carp development, and no significant difference was observed between Kohaku and Hi-Utsuri groups before 7 dph (P>0.05), while Hi-Utsuri group showed significantly higher enzyme activity than Kohaku group at the same stages after 7 dph (P<0.05). Tyrosinase activity showed an up-regulation trend with slight fluctuation during the development of koi carp, and peaked at the ocular pigment stage and on 23 dph (P<0.05). The enzyme activity was significantly higher in Hi-Utsuri group than in Kohaku group at each developmental stage (P<0.05), which indicates that tyrosinase and cystinase activities were closely associated with pigment cell development of koi carp. The expressions of agouti, mc1r, mitf and tyr mRNAs peaked in gastrula and blastula periods (P<0.01), then decreased. Thus, agouti, mc1r, mitf and tyr mRNAs might play an important role in the formation of body colors in early embryonic development.