Genes responsible for the formation of asymmetrical mandibular teeth in the giant mealworm beetle, Zophobas atratus

ABSTRUCTThe mandibles of coleopteran insects are typical examples of external morphological asymmetry in animals. The developmental molecular mechanisms underlying the external morphological asymmetry remain to be elucidated compared to those of the internal asymmetric organ. In the tenebrionid beetle, Zophobas atratus, the inner teeth of adult mandibles are asymmetric, while the pupal mandibles are nearly symmetric. The asymmetric morphogenesis is assumed to be caused by the left-right regulatory differences of inner teeth formation, but even the developmental mechanisms involved in the inner teeth per se remains unknown. In this study, we investigated the morphogenetic process involved in the formation of inner teeth and searched for genes responsible for this process. Morphological observation showed that the inner teeth of adults formed during 0-5 days after pupal molting. Left mandibles possessed the characteristic second inner teeth, whereas the right mandibles exhibited invaginations between apical and second inner teeth. We performed RNAi for candidate genes and successfully identified four genes (paired, alistaless, Lim1, and mlpt) involved in the formation of inner teeth. Among them, mlpt RNAi had a strong effect on the morphology of the right mandibles, suggesting its involvement in the asymmetrical formation of mandibles.