Analysis of an Exon Cassette of a Hyperdivers Immune Gene in Insects

Abstract

SUMMARY Beneficial insects such as honeybees and silkworms are threatened by numerous pests, parasites and pathogens. However, pest insects as m uch as beneficial species also often acquire infectious diseases, which can potentially be used for pest control. To take advantage of pathogens infecting pest species, detailed knowl edge of the immune system of pest insects is necessary. Here, the immune gene Down syndrome cell adhesion molecule (Dscam) is studied in Australian bulldog and jumper ants, whos e venom can cause a fatal anaphylactic shock in humans. In insects, Dscam shows extraordinary genetic diversity through alternative splicing. More than 12000 alternative splice varian ts are estimated being transcribed in the Western honeybee. To understand better the function and evolution of Dscam, one of the four variable exon cassettes was sequenced from six Myrmecia ant species. Using a comparative codon-based model, the results do not indicate any evidence of adaptive evolution in the analysed data set. Corroborating previous studies, the comparison of Dscam in ants and other insects including the Western honeybee and silkworms demonstrates high similarity of this gene across insect orders and suggests a conserved function of this gene.