Deciphering the genetic interactions between Pou4f3, Gfi1, and Rbm24 in maintaining cochlear hair cell survival

ABSTRACT Mammals harbor a limited number of sound-receptor hair cells (HCs) that cannot be regenerated after damage. Thus, investigating the underlying molecular mechanisms that maintain HC survival is crucial for preventing hearing impairment. Intriguingly, Pou4f3 -/- or Gfi1 -/- HCs form initially but then rapidly degenerate, whereas Rbm24 -/- HCs degenerate considerably later. However, the transcriptional cascades involving Pou4f3, Gfi1, and Rbm24 remains undescribed. Here, we demonstrate that Rbm24 expression is completely repressed in Pou4f3 -/- HCs but unaltered in Gfi1 -/- HCs, and further that the expression of both POU4F3 and GFI1 is intact in Rbm24 -/- HCs. Moreover, by using in vivo mouse transgenic reporter assays, we identify three Rbm24 enhancers to which POU4F3 binds. Lastly, through in vivo genetic testing of whether Rbm24 restoration alleviates the degeneration of Pou4f3 -/- HCs, we show that ectopic Rbm24 alone cannot prevent Pou4f3 -/- HCs from degenerating. Collectively, our findings provide new molecular and genetic insights into how HC survival is regulated.