Overlapping Activities of Two Neuronal Splicing Factors Switch the GABA Effect from Excitatory to Inhibitory by Regulating REST

Abstract

SUMMARY A truncating mutation in the mouse Srrm4 gene, which encodes a neuronal splicing factor, causes alternative splicing defects selectively in the ear. The mechanism by which splicing is preserved in the brain of these mice is not known. Here, we show that SRRM3 limits the Srrm4 mutation-associated defects to the ear and that, in cortical neurons, overlapping SRRM3-SRRM4 activity regulates the development of interneuronal inhibition. In vitro, SRRM3 and SRRM4 regulate the same splicing events, but a mutation in mouse Srrm3 causes tremors and mild defects in neuronal alternative splicing, demonstrating unique SRRM3 roles in vivo. Mice harboring mutations in both Srrm3 and Srrm4 die neonatally and exhibit severe splicing defects. In these mice, splicing alterations prevent inactivation of the gene repressor REST, which maintains immature excitatory GABAergic neurotransmission by repressing K-Cl cotransporter 2. Thus, our data reveal that SRRM3 and SRRM4 act redundantly to regulate GABAergic neurotransmission by inactivating REST.

Cell-type, single-cell, and spatial signatures of brain-region specific splicing in postnatal development

“…Temporal and anatomic differences in alternative splicing are implicated in developmental changes in molecular function 70 . Our single-cell isoform data enable, for the first time, the illumination of alternative splicing regulation across cell types.…”

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

“…We previously showed that in cortical neurons SRRM4 and SRRM3 act redundantly in regulating the alternative splicing of Rest (Nakano et al, 2019). However, in the utricle, SRRM4 is critical for the alternative splicing of Rest (Fig 2B), likely because utricular expression of Srrm3 is minimal in the absence of SRRM4 (Fig 2A).…”

“…We tested whether Srrm3 expression is necessary for the Tg(DnRest)-dependent survival of IHCs and VHCs in Srrm4 bv/bv mice. To reduce Srrm3 expression in Tg(DnRest);Srrm4 bv/bv mice, we took advantage of a recently produced gene trap allele of Srrm3 (Srrm3 gt ) (Nakano et al, 2019). Tg(DnRest);Srrm3 gt/gt ;Srrm4 bv/bv mice were generated and used for qRT-PCR and histological analyses.…”

“…We previously reported that neurons do not require SRRM4 for the inclusion of exon 4 of Rest in the mature mRNA (Nakano et al, 2019). In these cells, SRRM4 and the related protein SRRM3 act redundantly to regulate the alternative splicing of Rest until Rest is transcriptionally silenced at around postnatal day (P) 16.…”

“…Right: Cellular outcomes in WT versus Srrm4 bv/bv mice. (B) Schematic of production of Tg (DnRest) brain, SRRM3 is required for Purkinje cell survival (Nakano et al, 2019); in the ear, its role has not been evaluated.…”