BmTrpA1-Mediated ILP/AKT/FOXO signaling Underlies Temperature-Dependent diapause in Silkworms, Bombyx mori

Diapause is a developmentally arrested state in insects induced by seasonal cues such as photoperiod and temperature. The scientific literature agrees on that the temperature-sensitive transient receptor potential ankyrin 1 (TRPA1) channel and insulin signaling pathway (ILP/AKT/FOXO) are both essential for diapause regulation, but their interactions remain unclear. This study investigates whether the ILP/AKT/FOXO pathway can mediate the temperature-dependent maternal embryonic diapause induced by the TRPA1 channel in Bombyx mori. We found that the maternal pupae primed for diapause-egg-production (25DD) and those primed for non-diapause-egg-production (15DD) significantly differ in temporal patterns of BmTrpA1 gene expression. Next, we used the BmTrpA1^-/- mutant, and showed that the mutation results in abolishing the transient peak of diapause hormone (DH) concentration in hemolymph, affects the protein profile of ILP, mRNA profiles of AKT and FOXO, and phosphorylation of FOXO protein. Generally, the profiles in BmTrpA1^-/- mutants were similar to those of 15DD pupae. In addition, we found that RNAi-mediated silencing of FOXO in the BmTrpA1^-/- mutant, or AKT in 15DD pupae, reduces or increases the diapause incidence, respectively. Collectively, our results indicate that the temperature-dependent diapause regulation by the TRPA1 channel is mediated by the ILP/AKT/FOXO pathway in the silkworm.