Dynamic eIF3‐S6 Phase Separation Switch Instructed by m ⁶ A Modification Drives the Molting of Locusts

Abstract Molting is critical for the development and growth of insects. A central juncture in molting is the periodic and coordinated regulation of molting‐responsive mRNAs, which are essential for degrading the old cuticle and forming a new one. Knowledge is lacking of how molting‐responsive molecules function cooperatively and timely. Here, multi‐stage m ⁶ A modification levels, m ⁶ A reader condensation, and transcriptome analyses are developed to track the dynamic functional coupling for molting signals. The results showed that the molting‐responsive mRNAs are downregulated with the decrease of m ⁶ A modification levels from pre‐molt to the molt stage. The eIF3‐S6 is further identified, as an m ⁶ A reader, can directly bind to EcR A ³³⁵ and Cht10 A ⁷⁵⁸⁹ . The low mRNA m ⁶ A modification in the molt stage facilitates eIF3‐S6 to undergo liquid–liquid phase separation (LLPS) by binding m ⁶ A‐containing EcR / Cht10 into condensed droplets for stabilizing the mRNAs. Disruption of m ⁶ A modification or breaking phase separation can cause a disorder of the new/old cuticle synthesis/degradation in molting. The disorder results in abnormal and unsuccessful molting, ultimately leading to the death of nymphs. Overall, the data mechanistically highlight an example of how two central machineries, m ⁶ A modification and LLPS, can accurately and functionally cooperate to optimize molting‐responsive gene expression for insect molting.