Inhibition of a transcriptional repressor rescues hearing in a splicing factor–deficient mouse

Abstract

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 (Srrm4bv/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 Srrm4bv/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 Srrm4bv/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.

Development in the Mammalian Auditory System Depends on Transcription Factors

“…Finally, loss of IHCs in Srrm4 mutants (a serine/arginine repetitive matrix 4 genes referred to as bv/bv mutations) shows that most type I afferent fibers reroute to OHCs (Figure 5B,G; [44,65]). Notably, the expression of dominant-negative REST in double Srrm3/4 mutants ablates all IHCs [95]. Previous work showed that delayed HCs loss, such as in Bdnf and Ntf3 double CKO mutants, results in delayed innervation [8].…”

Neurog1, Neurod1, and Atoh1 are essential for spiral ganglia, cochlear nuclei, and cochlear hair cell development

“…Pou4f3 ( Brn3c ) null mice, which develop only immature hair cells and have limited expression of neurotrophins 59 , show little effect on innervation patterns beyond the lack of innervation to outer hair cells (OHCs) birth. The absence of inner hair cells (IHCs), through the loss of Atoh1 or in Bronx-waltzer mutants, results in spiral ganglion projections to OHCs and disorganized central projections 10 , 60 , 61 ( Figure 2 ). Interestingly, replacing an allele of Atoh1 with Neurog1 in Atoh1 kiNeurog1 mice showed a different pattern of spiral ganglia projections to reach out the organ of Corti 62 , 63 ( Figure 2 ), consistent with a reduction in the number of neurons and hair cells 16 .…”

“…Using Pax2-cre to conditionally delete Dicer 89 resulted in incomplete hair cell loss compared with the total hair cell loss with Foxg1-cre conditional deletion, comparable to the equivalent conditional deletions of Gata3 75 , 139 . Finally, Bronx-waltzer mice, which are mutant for the gene Srrm4 ( Figure 4 ), lose IHCs and vestibular hair cells but retain OHCs 60 , 61 . OHCs, meanwhile, express Srrm3 independent of the Srrm4 gene downstream of REST 61 .…”

“…Finally, Bronx-waltzer mice, which are mutant for the gene Srrm4 ( Figure 4 ), lose IHCs and vestibular hair cells but retain OHCs 60 , 61 . OHCs, meanwhile, express Srrm3 independent of the Srrm4 gene downstream of REST 61 .…”

The crosstalk between the Notch, Wnt, and SHH signaling pathways in regulating the proliferation and regeneration of sensory progenitor cells in the mouse cochlea

“…The mammalian cochlea has very limited spontaneous hair cell (HC) regeneration ability, and such regeneration is only seen at embryonic or very early neonatal ages and the quantity and quality of this limited spontaneous HC regeneration cannot restore cochlear function (Jung et al 2013). When the inner ear sensory HCs are damaged, there is no spontaneous HC regeneration in the adult cochlea, and this leads to permanent hearing loss (Herranen et al 2020;Nakano et al 2020). Thus, stimulating sensory precursor cell proliferation and transdifferentiation into new HCs might be an effective method for rescuing hearing dysfunction (Yamoah et al 2020).…”