Submitted to: Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/12/2012
Publication Date: 4/1/2012
Citation: Arakane, Y., Lomakin, J., Gehrke, S.H., Hiromasa, Y., Tomich, J.M., Muthukrishnan, S., Beeman, R.W., Kramer, K.J., Kanost, M.R. 2012. Formation of rigid, non-flight forewings (elytra)of a bettle requires two major cuticular proteins. Science. 8(4): e1002682. http://dx.doi.org/10.1371/journal.pgen.1002682. Interpretive Summary: Chitinous structures on insects such as the exoskeleton and digestive sac are vital for insect survival and could be exploited by appropriately-targeted biopesticides. We identified two new structural proteins in the red flour beetle exoskeleton that are important for conferring strength and rigidity to the adult cuticle. The proteins are the major protein components of wing covers, but are also found in other rigid portions of the exoskeleton. Absence of the proteins in wing covers through genetic manipulation leads to dehydration and death of the insect. Our ongoing gene discovery efforts in this pest insect continue to reveal new weaknesses that may lead to new methods of insect control.
Technical Abstract: Insect cuticle is composed primarily of chitin and structural proteins. To study the function of structural cuticular proteins, we examined proteins present in elytra (modified forewings that become highly sclerotized and pigmented covers for the hindwings) of the red flour beetle, Tribolium castaneum. We identified two highly abundant proteins, TcCPR27 (10 kDa) and TcCPR18 (20 kDa), which are also present in pronotum and ventral abdominal cuticles. Both are members of the Rebers and Riddiford family of cuticular proteins and contain RR2 motifs. Transcripts for both genes dramatically increase in abundance at the pharate adult stage and then decline quickly thereafter. Injection of specific double-stranded RNAs for each gene into penultimate or last instar larvae had no effect on larval-larval, larval-pupal or pupal-adult molting. The elytra of the resulting adults, however, were short, wrinkled, warped and fenestrated. TcCPR27-deficient insects could not fold their hindwings properly and died approximately one week after eclosion, probably because of dehydration. TcCPR18-deficient insects exhibited a similar but less dramatic phenotype. Immunolocalization studies confirmed the presence of TcCPR27 in elytral cuticle. The elytra from both dsTcCPR27- and dsTcCPR18-treated insects were less rigid than those from control insects. These results demonstrate that TcCPR27 and TcCPR18 are major structural proteins in the rigid elytral, dorsal, thoracic and ventral abdominal cuticles of the red flour beetle, and that both proteins are required for morphogenesis of the beetle’s elytra.