Evolutionary conservation of bursicon in the animal kingdom

Bursicon bioactivity is essential for tanning of the exoskeleton and for wing spreading behavior that occur in newly emerged adult insects. Previously, we demonstrated that in the fruit fly, Drosophila melanogaster, bursicon exists as a heterodimeric cystine knot protein that activates the leucine-rich repeats containing G protein-coupled receptor 2 (DLGR2). By performing similarity based in silico searches in genomic and complementary DNA databases, we identified bursicon homologous sequences in several protostomian as well as deuterostomian invertebrates. In the genome of the honeybee, Apis mellifera, the coding regions for bursicon cystine knot subunits are organized in a genomic locus of approximately 4 kilobase pairs. Reverse transcription PCR analysis indicates that this region likely codes for two distinct bursicon cystine knot subunits. Our results illustrate the remarkable conservation of bursicon in invertebrate species and provide an avenue for functional analyses of this hormone in a wide range of animal species.