Insulin receptor-2 regulates 20-hydroxyecdysone synthesis and ecdysis in the German cockroach

The insulin/insulin-like growth factor signaling (IIS) pathway plays a central role in several vital physiological processes in animals. The identification of three insulin receptor (InR) (BgInR1, BgInR2 and BgInR3) in the genome of the cockroach Blattella germanica (L.) prompted us to investigate into their respective contribution to the regulation of different events. Previous studies from our group revealed that BgInR2 is the paralog that retains most of the activity in reproduction-related functions. In the present study, we focused in elucidating the roles of the three InR of B. germanica in molting and analyzed their involvement in the hormonal regulation underlying the different phases of this process. To do this, we first quantified the expression of several genes, including ecdysteroidogenic genes and those of peptide hormones involved in molting. Our findings indicate that the ecdysis triggering hormone (ETH) is an ecdysteroid-responsive gene. Furthermore, we analyzed the phenotype produced by RNAi-triggered specific depletion of BgInR1, BgInR2 and BgInR3, and identified BgInR2 as the key factor in IIS signaling related to molting. BgInR2 depletion produced a delay and dysregulation in ecdysone production, which in turn led to reduced and delayed ETH expression. Finally, this culminated in defective ecdysis and impaired exuviae shedding. Overall, our results demonstrate that the IIS pathway, via BgInR2, promotes ecdysone synthesis in the prothoracic gland, which subsequently induces ETH production to initiate and coordinate ecdysis.