RNA Interference-Aided Functional Characterization of Juvenile Hormone Signaling During Vitellogenesis in Two Coleoptera Species

In Tribolium castaneum, juvenile hormone (JH) signal, through Methoprene-tolerant (Met)/Taiman (Tai) heterodimer, regulates vitellogenesis. Considering that Coleoptera is by far the largest animal taxon, whether JH pathway controls vitellogenesis remains to be clarified in other Coleopteran species. In the current paper, temporal expression determination revealed that JH signal is triggered in the young female adults in two Henosepilachna species, consistent with active oogenesis and vitellogenesis in these beetles. Aided by RNA interference (RNAi), we knocked down a JH biosynthesis gene Hvpjhamt and a JH receptor gene HvpMet in Henosepilachna vigintioctopunctata, and two JH receptor genes HvmMet and HvmTai in H. vigintioctomaculata. The knockdown significantly inhibited JH signal. As a result, the oviposition is greatly reduced and the vitellogenesis is significantly delayed in the two Henosepilachna species. Little yolk substances were seen in the oocytes in the Hvpjhamt and HvpMet RNAi ovaries, in contrast to larger amount of yolk granules in the normal oocytes in H. vigintioctopunctata. Correspondingly, the transcript levels of Vg in the fat bodies and of VgR in the ovaries were significantly lowered in the Hvpjhamt, HvpMet, HvmMet, and HvmTai RNAi samples. Therefore, our findings suggest that JH signal, mediating through Met/Tai complex, plays a key role in Vg synthesis and uptake in the two Coleopteran species.