title: 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.
authors.affiliation: UCL Ear Institute, University College London, London, United Kingdom.
authors.forename: Andrew
authors.identifier: 0000-0002-0995-0219
authors.initials: A
authors.lastname: Forge
authors.affiliation: UCL Ear Institute, University College London, London, United Kingdom.
authors.forename: Ruth R
authors.initials: RR
authors.lastname: Taylor
authors.affiliation: UCL Ear Institute, University College London, London, United Kingdom.
authors.forename: Sally J
authors.identifier: 0000-0002-4421-2043
authors.initials: SJ
authors.lastname: Dawson
authors.affiliation: National Heart and Lung Institute, Imperial College London, London, United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Lovett
authors.affiliation: UCL Ear Institute, University College London, London, United Kingdom.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Jagger
mesh_terms: D000367:Age Factors; D000818:Animals; D005786:Gene Expression Regulation; D006199:Hair Cells, Auditory, Inner / Q000378:metabolism* / Q000473:pathology; D034381:Hearing Loss / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D007150:Immunohistochemistry; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009925:Organ of Corti / Q000378:metabolism / Q000503:physiopathology / Q000648:ultrastructure; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D059547:Stereocilia / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
chemical_list: D009419:Nerve Tissue Proteins; D011956:Receptors, Cell Surface; C426856:SorCS2 protein, mouse