20E-induced <i>Kr-h1</i> expression facilitates developmental transitions depending on chromosome accessibility of <i>BR-C</i> enhancers.

Abstract

Transcription factors and histone modification-mediated chromatin accessibility coordinately regulate spatiotemporal expression of genes that control growth and development. It is well documented that juvenile hormone-activated Kr-h1 antagonizes 20-hydroxyecdysone (20E)-induced expression of the pupal specifier <i>BR-C</i> to sustain larval status in holometabolous insects. Here, we revealed that during the larval-prepupal transition in <i>Drosophila melanogaster</i>, the 20E-activated <i>Kr-h1-BR-C</i> axis is a prerequisite for wing disc morphogenesis. Mechanistically, 20E-EcR/USP-Met-Tai directly activates Kr-h1 that upregulates <i>BR-C</i> expression via the positive Kr-h1 binding sites (PKBS) in the <i>BR-C</i> enhancers. Furthermore, we showed that 20E-induced H3K27 acetylation increases chromatin accessibility of the PKBS-containing enhancers, facilitating the maximum of <i>BR-C</i> expression that promotes developmental transitions. Collectively, in response to different hormone stimuli, a single transcription factor either negatively or positively regulates the expression of the same target gene depending on chromatin accessibility of its different enhancer regions, thus manipulating distinct developmental events.