In mechanosensory hair cells (HCs) of the ear, the transcriptional repressor REST is continuously inactivated by alternative splicing of its pre-mRNA. This mechanism of REST inactivation is crucial for hearing in humans and mice. Rest is one of many pre-mRNAs whose alternative splicing is regulated by the splicing factor SRRM4; Srrm4 loss-of-function mutation in mice (Srrm4 bv/bv ) causes deafness, balance defects, and degeneration of all HC types other than the outer HCs (OHCs). The specific splicing alterations that drive HC degeneration in Srrm4 bv/bv mice are unknown, and the mechanism underlying SRRM4-independent survival of OHCs is undefined. Here, we show that transgenic expression of a dominant-negative REST fragment in Srrm4 bv/bv mice is sufficient for long-term rescue of hearing, balancing, HCs, alternative splicing of Rest, and expression of REST target genes including the Srrm4 paralog Srrm3 We also show that in HCs, SRRM3 regulates many of the same exons as SRRM4; OHCs are unique among HCs in that they transiently down-regulate Rest transcription as they mature to express Srrm3 independently of SRRM4; and simultaneous SRRM4-SRRM3 deficiency causes complete HC loss by preventing inactivation of REST in all HCs. Thus, our data reveal that REST inactivation is the primary and essential role of SRRM4 in the ear, and that OHCs differ from other HCs in the SRRM4-independent expression of the functionally SRRM4-like splicing factor SRRM3.
© 2020 Nakano et al.