Peguero, B. | bioRxiv Science

bioRxiv2025

CASZ1 regulates the rate at which outer hair cells mature and is required for hearing

The transcriptional activator ATOH1 is a master regulator of the development of mechanosensory hair-cells (HCs) in the ear. We report that the ATOH1 target gene Casz1 encodes a transcription factor that regulates the rate of outer HC (OHC) maturation by gene repression. Genetic deletion of Casz1 during (but not after) development of the mouse cochlea caused: hearing loss; abnormal organization of mechanosensory stereocilia bundles in OHCs; abnormally low F-actin density in OHC cuticular plates; progressive loss of OHCs; and mild morphological alterations in inner HCs. RNA sequencing revealed that Casz1 deletion delayed downregulation of genes expressed in immature OHCs, including the actin regulator-encoding gene Coro2a, and accelerated upregulation of genes expressed in mature OHCs. Coro2a knockdown restored the density of cuticular plate F-actin in Casz1 mutant OHCs. Our data indicate that CASZ1 regulates transcriptional and morphological maturation of OHCs, and that CASZ1 in maturing HCs is necessary for hearing.

developmental biology↗

bioRxiv2023

Genetic and pharmacologic alterations of claudin9 levels suffice to induce functional and mature inner hair cells

Hearing loss is the most common form of sensory deficit. It occurs predominantly due to hair cell (HC) loss. Mammalian HCs are terminally differentiated by birth, making HC loss challenging to replace. Here, we show the pharmacogenetic downregulation of Cldn9, a tight junction protein, generates robust supernumerary inner HCs (IHCs) in mice. The ectopic IHC shared functional and synaptic features akin to typical IHCs and were surprisingly and remarkably preserved for at least fifteen months >50% of the mouses life cycle. In vivo, Cldn9 knockdown using shRNA on postnatal days (P) P2-7 yielded analogous functional ectopic IHCs that were equally durably conserved. The findings suggest that Cldn9 levels coordinate embryonic and postnatal HC differentiation, making it a viable target for altering IHC development pre- and post-terminal differentiation.

neuroscience↗