SUMMARYTyrosinase provides an essential activity during egg production in diverse platyhelminths by mediating sclerotization of eggshells. In this study, we investigated the genomic and evolutionary features of tyrosinases in parasitic platyhelminths whose genomic information is available. A pair of paralogous tyrosinases was detected in most trematodes, whereas they were lost in cyclophyllidean cestodes. A pseudophyllidean cestode displaying egg biology similar to that of trematodes possessed an orthologous gene. Interestingly, one of the paralogous tyrosinases appeared to have been multiplied into three copies in Clonorchis sinensis and Opisthorchis viverrini. In addition, a fifth tyrosinase gene that was minimally transcribed through all developmental stages was further detected in these opisthorchiid genomes. Phylogenetic analyses demonstrated that the tyrosinase gene has undergone duplication at least three times in platyhelminths. The additional opisthorchiid gene arose from the first duplication. A paralogous copy generated from these gene duplications, except for the last one, seemed to be lost in the major neodermatans lineages. In C. sinensis, tyrosinase gene expressions were initiated following sexual maturation and the levels were significantly enhanced by the presence of O2 and bile. Taken together, our data suggest that tyrosinase has evolved lineage-specifically across platyhelminths related to its copy number and induction mechanism.
Class III nucleotide cyclases in bacteria and archaebacteria: lineage-specific expansion of adenylyl cyclases and a dearth of guanylyl cyclases
