Rbm24 promotes outer hair cell survival through Insm1 repression while independently regulating hair bundle morphogenesis

The inactivation of Rbm24, an RNA-binding protein, leads to cell death and hair bundle defects in cochlear outer hair cells (OHCs). However, the underlying molecular mechanisms remain unclear. To address this, we have performed comprehensive transcriptomic profiling of purified wild-type and Rbm24-/- mouse OHCs at postnatal day 7 (P7). Loss of Rbm24 perturbs numerous genes associated with hair bundle morphogenesis and delays the overall OHC differentiation program. Insm1, a key transcription factor normally downregulated by P2, remains aberrantly and persistently expressed in Rbm24-/- OHCs. Overexpression of Insm1 alone induces OHC death, whereas simultaneous inactivation of Rbm24 and Insm1 largely rescues OHC survival but only partially restores hair bundle morphology. It demonstrates that Rbm24 promotes OHC survival independently of its role in regulating hair bundle morphogenesis. Collectively, our findings establish Rbm24 as a dual-function regulator that ensures OHC survival by acting as a critical repressor of Insm1 expression, while independently orchestrating hair bundle assembly. These results highlight the central role of Rbm24 in coordinating OHC differentiation and structural maturation, and provide insights into potential molecular targets for hair cell regeneration.