23rd Conference of European Comparative Endocrinologists edition:23 location:Manchester (U.K.) date:29 August - 2 September
Bursicon bioactivity, essential for tanning, i.e. melanization and hardening, of the exoskeleton and for wing spreading behavior during the final phase of insect metamorphosis, was already described more than forty years ago. Since then, however, its molecular nature remained elusive. Based on partial amino acid sequences derived from cockroach bursicon preparations the Drosophila genome was searched for putative bursicon-encoding sequences and two distantly related cystine knot proteins were identified. Unexpectedly, in the genome of the honeybee, Apis mellifera, the genes coding for the Drosophila protein homologs were predicted to be fused. This observation was taken as an evolutionary indication that both Drosophila proteins would likely interact, thereby possibly forming a bioactive heterodimer. Indeed, when both cystine knot proteins were co-expressed in mammalian cells, the resulting conditioned medium evoked strong tanning of the exoskeleton in freshly eclosed, neck-ligated flesh flies (Neobellieria bullata). In addition, the same medium was shown to activate the previously orphan Drosophila leucine-rich repeats containing G protein-coupled receptor 2 (dLGR2) in a dose-dependent manner. In conclusion, we unambiguously demonstrated that the Drosophila neurohormone bursicon is a heterodimer made of two cystine knot polypeptides and the natural agonist of dLGR2.