Insulin/IGF signaling and TORC1 promote vitellogenesis via inducing juvenile hormone biosynthesis in the American cockroach

ABSTRACTVitellogenesis, including vitellogenin (Vg) production in the fat body and Vg uptake by maturing oocytes, is of great importance for the successful reproduction of adult females. The endocrinal and nutritional regulation of vitellogenesis differs distinctly in insects. Here, the complex crosstalk between juvenile hormone (JH) and the two nutrient sensors insulin/IGF signaling (IIS) and target of rapamycin complex1 (TORC1), was investigated to elucidate the molecular mechanisms of vitellogenesis regulation in the American cockroach, Periplaneta americana. Our data showed that a block of JH biosynthesis or JH action arrested vitellogenesis, in part by inhibiting the expression of doublesex (Dsx), a key transcription factor gene involved in the sex determination cascade. Depletion of IIS or TORC1 blocked both JH biosynthesis and vitellogenesis. Importantly, the JH analog methoprene, but not bovine insulin (to restore IIS) and amino acids (to restore TORC1 activity), restored vitellogenesis in the neck-ligated (IIS-, TORC1- and JH-deficient) and rapamycin-treated (TORC1- and JH-deficient) cockroaches. Combining classic physiology with modern molecular techniques, we have demonstrated that IIS and TORC1 promote vitellogenesis, mainly via inducing JH biosynthesis in the American cockroach.

Insulin/IGF signaling and TOR promote vitellogenesis via inducing juvenile hormone biosynthesis

ABSTRACTVitellogenesis, including vitellogenin (Vg) production in the fat body and Vg uptake by maturing oocytes, is of great importance for the successful reproduction of adult females. The endocrinal and nutritional regulation of vitellogenesis differs distinctly in insects. Here, the complex crosstalk between juvenile hormone (JH) and the two nutrient sensors, insulin/IGF signaling (IIS) and target of rapamycin (TOR), was investigated to elucidate the molecular mechanisms regulating vitellogenesis in the American cockroach, Periplaneta americana. Our data showed that a block of JH biosynthesis or JH action arrested vitellogenesis, partially by inhibiting the expression of doublesex (Dsx), a key transcription factor gene involved in the sex determination cascade. Depletion of IIS and TOR blocked both JH biosynthesis and vitellogenesis. Importantly, the JH analog methoprene, but not bovine insulin (to restore IIS) and amino acids (to restore TOR activity), restored vitellogenesis in the neck-ligated (both nutrient- and JH-deficient) cockroaches. Combining classic physiology with modern molecular techniques, we have demonstrated that JH signaling alone is able to induce vitellogenesis and thus ovarian maturation. By contrast, IIS and TOR do not induce vitellogenesis independent of JH, the nutrient sensors promote vitellogenesis in an indirect manner via activating JH biosynthesis.