Disruption of SorCS2 reveals differences in the regulation of stereociliary bundle formation between hair cell types in the inner ear

Abstract

Behavioural anomalies suggesting an inner ear disorder were observed in a colony of transgenic mice. Affected animals were profoundly deaf. Severe hair bundle defects were identified in all outer and inner hair cells (OHC, IHC) in the cochlea and in hair cells of vestibular macular organs, but hair cells in cristae were essentially unaffected. Evidence suggested the disorder was likely due to gene disruption by a randomly inserted transgene construct. Whole-genome sequencing identified interruption of the SorCS2 (Sortilin-related VPS-10 domain containing protein) locus. Real-time-qPCR demonstrated disrupted expression of SorCS2 RNA in cochlear tissue from affected mice and this was confirmed by SorCS2 immuno-labelling. In all affected hair cells, stereocilia were shorter than normal, but abnormalities of bundle morphology and organisation differed between hair cell types. Bundles on OHC were grossly misshapen with significantly fewer stereocilia than normal. However, stereocilia were organised in rows of increasing height. Bundles on IHC contained significantly more stereocilia than normal with some longer stereocilia towards the centre, or with minimal height differentials. In early postnatal mice, kinocilia (primary cilia) of IHC and of OHC were initially located towards the lateral edge of the hair cell surface but often became surrounded by stereocilia as bundle shape and apical surface contour changed. In macular organs the kinocilium was positioned in the centre of the cell surface throughout maturation. There was disruption of the signalling pathway controlling intrinsic hair cell apical asymmetry. LGN and Gαi3 were largely absent, and atypical Protein Kinase C (aPKC) lost its asymmetric distribution. The results suggest that SorCS2 plays a role upstream of the intrinsic polarity pathway and that there are differences between hair cell types in the deployment of the machinery that generates a precisely organised hair bundle.

Retinoic acid degradation shapes zonal development of vestibular organs and sensitivity to transient linear accelerations

“…The preparation of samples for SEM was conducted as described 75 . Briefly, the utricles and cristae were quickly dissected from harvested animals and submerged in fresh fixative consisting of 2.5% glutaraldehyde (Electron Microscopy Sciences), 2% formaldehyde (EMS), 3 mM calcium chloride, and 0.1 M cacodylate.…”

Daple coordinates organ-wide and cell-intrinsic polarity to pattern inner-ear hair bundles

“…Atypical protein kinase C (aPKC) forms a complementary domain on the opposite side of the cell. Disruption of this network disrupts the position of the kinocilium on the apical surface, resulting in a split or otherwise misshapen hair bundle ( 6 – 9 ).…”

Characterization of the microRNA Transcriptomes and Proteomics of Cochlea Tissue-derived Small Extracellular Vesicles From Different Age of Mice After Birth

“…6c). Most of these proteins are reported to be involved in neurodevelopmental process [77], cilia formation [78], ion homeostasis [79], cell proliferation and differentiation [80], and signaling [81]. These results suggest that the expression patterns of proteins in the cochlear tissue-derived sEVs are correlated with age and may play signi cant roles in the formation of the inner ear system.…”

“…Among the proteins that decrease with age, Hnrnp [110], Ddx5 [111], Ilf3 [112], Lamtor5 [113], Psmd2 [114], Ddb1 [115], Psmd6 [116], and Chd4 [117] are reported to related to cell proliferation and differentiation. Ptbp1 [118], Chd4 [119], Ruvbl2 [120], Cul4a [121], and Lama4 [122] are required for early developmental processes and neuronal differentiation, and some proteins also presented in the inner ear, such as P3h1 [123], Sorcs2 [78], Panx3 [124,125], Idh1 [126], Lamb1 [127]. P3h1 knockout mice showed dysplasia of middle ear bones and hearing impairment [123].…”