Dynamic eIF3‐S6 Phase Separation Switch Instructed by m6A Modification Drives the Molting of Locusts

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 m6A modification levels, m6A 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 m6A modification levels from pre-molt to the molt stage. The eIF3-S6 is further identified, as an m6A reader, can directly bind to EcR A335 and Cht10 A7589. The low mRNA m6A modification in the molt stage facilitates eIF3-S6 to undergo liquid-liquid phase separation (LLPS) by binding m6A-containing EcR/Cht10 into condensed droplets for stabilizing the mRNAs. Disruption of m6A 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, m6A modification and LLPS, can accurately and functionally cooperate to optimize molting-responsive gene expression for insect molting.