Role of scalloped in the post-embryonic development of the red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae)

Abstract

scalloped (sd) plays a key role in concert with vestigial (vg) in wing development in Drosophila melanogaster Meigen. We previously showed that as well as its conserved role in wing formation in the 28-spotted ladybird beetle Henosepilachna vigintioctopunctata (Fabricius), sd has a novel function in pupal ecdysis. However, the molecular mechanism responsible remains unknown. To determine whether the function of sd in pupal ecdysis was conserved among Coleoptera, we performed expression and functional analyses of sd in the red flour beetle, Tribolium castaneum (Herbst). T. castaneum sd (Tc-sd) mRNA was present continuously from the embryonic stage to the adult. The RNAi-mediated knockdown of Tc-sd in the larval stage resulted in arrest either in the intermolt phase or during larva-to-larva molting. Prepupae injected with Tc-sd dsRNA were arrested as pupae with shorter wings, while its injection in the early pupal stage resulted in arrest as pharate adults. These results suggested that Tc-sd may be involved in growth, molting, and wing formation. The transcript levels of the genes involved in ecdysone biosynthesis, the ecdysone cascade, and chitin biosynthesis were not markedly affected by the knockdown of Tc-sd, which indicated that Tc-sd knockdown did not affect ecdysone biosynthesis or its cascade directly.