Bursicon, the cuticle sclerotizing hormone—comparison of its molecular mass in different insects

Abstract

We have shown in a recent study that bursicon, which induces the tanning of the cuticle in freshly molted insects, is a 30 kDa protein in the meal beetle Tenebrio molitor. We now show that bursicon in the insect species Calliphora erythrocephala, Periplaneta americana, Gryllus bimaculatus and Locusta migratoria is also a protein of about 30 kDa. The determination of bursicon's molecular mass was accomplished by SDS-PAGE of nervous system homogenates, subsequent division of the gel into slices, protein elution from these slices, and a test for bursicon activity of the eluted proteins in the ligated fly bioassay. Bursicon activity can only be eluted from one gel slice spanning the molecular mass around 30 kDa. Dose-response curves for bursicon of different ventral ganglia show that there are appreciable differences in the bursicon content between thoracic and abdominal ganglia and between developmental stages. These differences vary from insect to insect. An attempt to determine the molecular mass of Manduca sexta bursicon was not possible because the ligated fly bioassay does not work with homogenates of the nervous system of Manduca. Homogenates of abdominal ganglia of Homarus americanus show a positive score in the ligated fly bioassay but not those of its thoracic ganglia. The results indicate that bursicon may have a similar structure throughout the arthropods, but with distinct exceptions.