Mi-2 and E93 coordinate robust cell cycle exit with terminal differentiation through enhancer decommissioning [ATAC-seq]

Many postmitotic tissues coordinate robust cell cycle exit with the progression of terminal differentiation. While the signals involved in initiating cell cycle exit during terminal differentiation for some tissues have been described, less is known about the mechanisms that maintain a stable, non-cycling state. We previously found that chromatin accessibility changes at a subset of rate-limiting cell cycle genes occurs during maintenance of cell cycle exit, suggesting chromatin remodelers may play a key role in maintaining a robust postmitotic state during terminal differentiation. Here we show that the chromatin remodeler Mi-2 is required to ensure a stable, postmitotic state in Drosophila eyes and wings. Mi-2 alters chromatin accessibility and gene expression during cell cycle exit and terminal differentiation. Mi-2 and a transcription factor involved in tissue maturation, E93, close chromatin accessibility at an overlapping subset of potential enhancers that include the rate-limiting mitotic regulator string (cdc25c) and genes involved in the progression of terminal differentiation. E93 is also required for a stable, postmitotic state and we verified in vivo that Mi-2 and E93 cooperate to decommission an enhancer for the essential mitotic regulator string, to coordinate the transition to a postmitotic state with terminal differentiation. Enhancer decommissioning at the string locus provides a molecular explanation for the long-term, nearly irreversible postmitotic state observed in many tissues as terminal differentiation progresses. ATAC-seq for Mi-2 manipulations with controls in 24h and 44h APF Drosophila eyes