Diversity of melanin synthesis genes in insects

Melanins are tyrosine-derived pigments that are ubiquitous in animals, plants, and fungi. Melanins are often associated with black and brown pigmentation, which provide a variety of biological functions, such as mimicry, camouflage, thermoregulation, and UV protection. The synthetic pathway of melanin pigments has been extensively studied in vertebrates, but interestingly, it has become clear that the kinds of melanin pigments and genes involved in melanin biosynthesis differ significantly between insects and vertebrates. Dopamine melanin is the major melanin pigment in various insects. In insects, most of the melanin synthesis genes are highly conserved, but the yellow family genes and aaNAT family genes exhibit diversity in gene repertoire among diverse insect taxa. In this review, we introduce eight melanin synthesis genes involved in insect epidermal pigmentation: tyrosine hydroxylase ( TH ), dopa decarboxylase ( DDC ), aspartate 1-decarboxylase ( ADC, black ), N - β - alanyldopamine synthase ( NBADS , ebony ), N - β - alanyldopamine hydrolase ( NBADH , tan ), a rylalkylamine N-acetyltransferase ( aaNAT ), multicopper oxidase 2 ( MCO2 , laccase2 ), and yellow . For each gene, we show the molecular phylogenetic tree based on the amino acid sequences of six representative insects, the fruit fly Drosophila melanogaster (Diptera), the silkworm Bombyx mori (Lepidoptera), the swallowtail butterfly Papilio xuthus (Lepidoptera), the red flour beetle Tribolium castaneum (Coleoptera), the honeybee Apis mellifera (Hymenoptera), and the blue-tailed damselfly Ischnura senegalensis (Odonata), which highlights the diversity of melanin synthesis genes among insects. We also introduce the current knowledge of the melanin synthesis gene that contribute to colour pattern formation in various insects.