Cuticle tanning in Tribolium castaneum

Abstract

Insect cuticle tanning (sclerotization and pigmentation) is a complex process that involves the production of quinones and quinone methides from catechols, followed by their oxidative conjugation with cuticular proteins, a process that leads to cuticle hardening and darkening. Using RNA interference (RNAi) methodology, we previously demonstrated that laccase 2 is the gene encoding the enzyme catalyzing cuticle tanning in the red flour beetle, T. castaneum. By searching Beetlebase, we identified several genes that are probably involved in the synthesis of catechols that are potential laccase 2 substrates, such as tyrosine hydroxylase (TH), dopa decarboxylase (DDC), dopamine N‐acetyltransferase (NAT) and aspartate α‐decarboxylase (ADC/black). To further clarify the metabolic pathway responsible for cuticle tanning and to determine the influence of different catechols on sclerotization and pigmentation, double stranded RNAs (dsRNAs) for each of those genes were injected into Tribolium and the resulting phenotypes analyzed in terms of morphology, pigmentation, and mRNA levels.