Molecular cloning, gene expression in albino mutants and gene knockdown studies of tyrosinase mRNA in rainbow trout

Tyrosinase has a role in melanin synthesis and several defects of the tyrosinase gene lead to albinism. Here, we cloned and characterized rainbow trout tyrosinase cDNAs and carried out the molecular and biochemical characterization of albino mutants. Two types of cDNA were cloned: tyrosinase-1 (Tyr-1) and tyrosinase-2 (Tyr-2). Both contained regions predicted to encode structural features of tyrosinase, and phylogenetic analysis confirmed that Tyr-1 and Tyr-2 were members of the tyrosinase family. Tyr-1 transcripts were first detected in embryos at 5 d post-fertilization (dpf) and Tyr-2 transcripts at 15 dpf. 3,4-dihydroxyphenylalanine assays revealed significantly reduced tyrosinase activities in dominant and recessive albino mutants compared with wild-type embryos. However, reverse-transcription PCR showed no differences in the amounts or lengths of the coding regions of Tyr-1 and Tyr-2 transcripts between wild-type embryos and albino mutants. Antisense morpholino oligonucleotides (AMOs) designed to knockdown tyrosinase gene expression in wild-type embryos led to reduced pigmentation in the retina and skin of embryos at 25 and 35 dpf, respectively. Furthermore, the tyrosinase activities of AMO-treated embryos were significantly reduced. We conclude that both Tyr-1 and Tyr-2 are crucial for melanin synthesis in rainbow trout embryos. Furthermore, we describe a potential application of AMOs in the treatment of hyperpigmentation.