Histone H3K27 methylation–mediated repression of Hairy regulates insect developmental transition by modulating ecdysone biosynthesis

Significance PRC2-mediated H3K27 methylation functions in epigenetic transcriptional repression and is involved in various developmental processes in eukaryotes. Insect developmental transitions are regulated by juvenile hormone (JH) and ecdysone in an antagonistic manner. Here, we used Bombyx and Drosophila to show that PRC2-mediated H3K27 methylation at the Hairy gene involved in JH signaling suppresses Hairy transcription in the prothoracic gland (PG), which is required for steroidogenic enzyme transcription, ecdysone biosynthesis, and the larval–pupal transition. JH impairs PRC2-mediated H3K27 methylation in the PG. Our findings establish an essential role for PRC2-mediated H3K27 methylation in hormone-mediated developmental transitions and further deepen our understanding of epigenetic regulatory mechanisms underlying the antagonistic actions of JH and ecdysone in insects.