Defective Gpsm2/Gαi3 signalling disrupts stereocilia development and growth cone actin dynamics in Chudley-McCullough syndrome

Abstract

Mutations in GPSM2 cause Chudley-McCullough syndrome (CMCS), an autosomal recessive neurological disorder characterized by early-onset sensorineural deafness and brain anomalies. Here, we show that mutation of the mouse orthologue of GPSM2 affects actin-rich stereocilia elongation in auditory and vestibular hair cells, causing deafness and balance defects. The G-protein subunit Gαi3, a well-documented partner of Gpsm2, participates in the elongation process, and its absence also causes hearing deficits. We show that Gpsm2 defines an ∼200 nm nanodomain at the tips of stereocilia and this localization requires the presence of Gαi3, myosin 15 and whirlin. Using single-molecule tracking, we report that loss of Gpsm2 leads to decreased outgrowth and a disruption of actin dynamics in neuronal growth cones. Our results elucidate the aetiology of CMCS and highlight a new molecular role for Gpsm2/Gαi3 in the regulation of actin dynamics in epithelial and neuronal tissues.

Gαi Proteins are Indispensable for Hearing

“…Using various Gnai mutant mouse lines we demonstrate that deficiency for Gα i3 but not Gα i2 produces high-frequency hearing loss, whereas the absence of both isoforms results in profound deafness resembling the phenotype seen in Gpsm2 mouse mutants [19,23].…”

“…So far, Gα i3 per se has not been associated with hereditary deafness because of an assumed functional Gα i isoform redundancy for hearing. Nevertheless, we and others recently reported hearing loss in Gα i3 cKO and Atoh1-PTX mice, correlating with stereociliary elongation defects in IHCs [19,23]. It remains open whether the ubiquitously expressed Gpsm2-binding partner Gα i2 has also an impact on cochlear architecture and auditory function and whether both Gα i proteins play specific and/or redundant roles.…”

“…Lower numbers and reduced elongation of stereocilia in high frequency cochlear turns in outer hair cells (OHCs) of Gnai3 cKO mice and stereociliary elongation defects in IHC in basal turns [19] correlated with the deficiency for Gnai3 in high frequency cochlear regions and high frequency hearing threshold loss. In contrast, due to an overlapping expression profile of Gα i2 and Gα i3 proteins we observed reduced numbers and impaired elongation of stereocilia together with low-frequency hearing threshold loss exclusively in the Gnai2/ i3 cKO mice which are deficient for both proteins.…”

“…All commercial antibodies were used as recommended by the manufacturers. Gα i1/i2 and Gα i3 -specific antibodies have been routinely validated with immunoblot and immunohistochemistry on wildtype and appropriate Gα i -deficient tissues [19,29,42]. For double labeling studies, both antibodies were simultaneously incubated for identical time periods.…”

“…Inhibiting Gα protein function with the pan-Gα i/oblocker PTX or via expression of an Atoh1-PTX construct demonstrated that Gα i and Gpsm2 control kinocilium migration and planar organization of stereociliary bundles in the hair cells of the murine cochlea [16,17]. Gpsm2 dysfunction has been linked to mutations in the GPSM2 gene in patients, formerly known as the deafness locus DFNB82, responsible for the autosomal recessive disorder Chudley-McCullough-syndrome [18,19] that is characterized by severe to profound congenital hearing loss in humans [20][21][22]. Moreover, knock-out mice revealed that the deletion of the Gα i3 isoform was sufficient to mimic the PTX phenotype in the immature pre-hearing organ by disrupting the migration of the kinocilium at the surface of hair cells and affecting hair bundle orientation and shape [16].…”