A Crucial Caste Regulation Gene Detected by Comparing Termites and Sister Group Cockroaches.

Sterile castes are a defining criterion of eusociality; investigating their evolutionary origins can critically advance theory. In termites, the soldier caste is regarded as the first acquired permanently sterile caste. Previous studies showed that juvenile hormone (JH) is the primary factor inducing soldier differentiation, and treatment of workers with artificial JH can generate presoldier differentiation. It follows that a shift from a typical hemimetabolous JH response might be required for soldier formation during the course of termite evolution within the cockroach clade. To address this possibility, analysis of the role of JH and its signaling pathway was performed in the termite and compared with the wood roach , a member of the sister group of termites. Treatment with a JH analog (JHA) induced a nymphal molt in RNA interference (RNAi) of JH receptor () was then performed, and it inhibited the presoldier molt in and the nymphal molt in Knockdown of in both species inhibited expression of 20-hydroxyecdysone (20E; the active form of ecdysone) synthesis genes. However, in , several 20E signaling genes were specifically inhibited by RNAi. Consequently, RNAi of these genes were performed in JHA-treated termite individuals. Knockdown of 20E signaling and nuclear receptor gene, (/) resulted in newly molted individuals with normal worker phenotypes. This is the first report of the JH-Met signaling feature in termites and JH-dependent molting activation is shared by both taxa and mediation between JH receptor and 20E signalings for soldier morphogenesis is specific to termites.