Identification of intermediate transcriptome states and synergistic effects of Isl1 in Atoh1-mediated cochlear hair cell conversion

Ectopic expression of Atoh1 in non-sensory supporting cells (SCs) in mouse cochleae induces their conversion to hair cells (HCs) in vivo. cHCs in multiple intermediate states of the conversion process that most closely resembled neonatal differentiating HCs, but differed from the progenitors. We further identified 52 transcription factors that are differentially expressed in cHCs, SCs, and mature HCs and confirmed that Isl1 synergistically enhanced the efficiency of Atoh1-mediated HC conversion in cochlear explants. Our results demonstrate that direct HC conversion from SCs in vivo follows a different path from normal development and requires multiple factors for maximum efficiency and completion. Overall design: Atoh1-HA was ectopically expressed in mouse supporting cells to convert into hair cells. The converted hair cells were labeled with tdTomato as well as a9 AChR-EGFP. Mouse supporting cells were labeled with tdTomato. Mouse outer hair cells were labeled with prestin-YFP using knockin strategy. Mouse inner hair cells were labeled with tdTomato.