Analysis of the proteomes of Tribolium castaneum elytra and hindwings: a comparison and contrast of hard and membranous cuticle

The insect cuticle is a remarkable material composed primarily of proteins embedded in a matrix of chitin fibers, with additional stability provided through cross-links with polyphenols. The composition of these components can produce cuticle that varies greatly in its physical properties from hard and rigid to soft and flexible. The elytra of beetles are modified forewings that are heavily sclerotized, and function as a protective covering for the hindwings which have a flexible, membranous cuticle. Thus, the elytra and hindwings of the red flour beetle, Tribolium castaneum, are two structures that offer the possibility of examining both hard and soft cuticle. For this analysis we have performed 2D gel electrophoresis and peptide mass fingerprinting on proteins extracted from the elytra and hindwings of newly molted adults, before sclerotization has occurred, . With this approach we have identified several members of the Rebers and Riddiford (RR) family of structural proteins; some being identified in both the elytra and hindwing while others were detected in only one appendage or the other. Also identified were chitin deacetylases, which may be involved in chitin metabolism. Additionally, we detected phenoloxidase and several members of the yellow gene family which may play a role in melanization and thus, have an effect on pigmentation or immunity. A large number of identified proteins were of unknown function and represent new and interesting classes to study.