Usher syndrome IIIA gene clarin-1 is essential for hair cell function and associated neural activation

Abstract

Usher syndrome 3A (USH3A) is an autosomal recessive disorder characterized by progressive loss of hearing and vision due to mutation in the clarin-1 (CLRN1) gene. Lack of an animal model has hindered our ability to understand the function of CLRN1 and the pathophysiology associated with USH3A. Here we report for the first time a mouse model for ear disease in USH3A. Detailed evaluation of inner ear phenotype in the Clrn1 knockout mouse (Clrn1(-/-)) coupled with expression pattern of Clrn1 in the inner ear are presented here. Clrn1 was expressed as early as embryonic day 16.5 in the auditory and vestibular hair cells and associated ganglionic neurons, with its expression being higher in outer hair cells (OHCs) than inner hair cells. Clrn1(-/-) mice showed early onset hearing loss that rapidly progressed to severe levels. Two to three weeks after birth (P14-P21), Clrn1(-/-) mice showed elevated auditory-evoked brainstem response (ABR) thresholds and prolonged peak and interpeak latencies. By P21, approximately 70% of Clrn1(-/-) mice had no detectable ABR and by P30 these mice were deaf. Distortion product otoacoustic emissions were not recordable from Clrn1(-/-) mice. Vestibular function in Clrn1(-/-) mice mirrored the cochlear phenotype, although it deteriorated more gradually than cochlear function. Disorganization of OHC stereocilia was seen as early as P2 and by P21 OHC loss was observed. In sum, hair cell dysfunction and prolonged peak latencies in vestibular and cochlear evoked potentials in Clrn1(-/-) mice strongly indicate that Clrn1 is necessary for hair cell function and associated neural activation.

Clarin-1 gene transfer rescues auditory synaptopathy in model of Usher syndrome

“…CLRN1 isoform 2 encodes a 232-amino acid tetraspan-like glycoprotein (1,4,6). Studies of mutant mice lacking exon 1 of Clrn1 (7,8) and knockdown approaches in zebrafish (9,10) have revealed structural and functional defects of F-actin-enriched stereocilia in hair cells. Additional roles for clarin-1 have also been sought, as mouse Clrn1 transcripts have been detected in both hair cells and the auditory primary neurons, from embryonic day 16 (E16) to adult stages (1,11).…”

Alternative splice variants of the USH3A gene Clarin 1 (CLRN1)

“…12 The localization has been characterized in the mouse cochlea, where Clrn1 is expressed in hair cells and spiral ganglion cells, 7,12 and the absence of Clrn1 in null mice leads to disorganization of the hair cell stereocilia. 10,13 In the murine retina, Clrn1 expression was found in Müller glia, 10 whereas immunohistochemical analyses suggest protein localization in the photoreceptor connecting cilia, inner segments, and ribbon synapses. 12 The pathophysiology of USH3 remains unexplained.…”

Clarin-1 acts as a modulator of mechanotransduction activity and presynaptic ribbon assembly

“…Amino acid alignments between clarin-1 and different members of the 4TM hyperfamily established a modest degree of similarity with stargazin, a calcium channel subunit involved in expression, mobilization, and clustering of AMPA (-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors at the synaptic cleft. Since in the inner ear, clarin-1 is not only present at the apical and basal aspects of the hair cells but also in the afferent neurons that innervate them, a similar role in synaptic shaping has been suggested (Adato et al, 2002;Chen et al, 2003;Geng et al, 2009;Zallocchi et al, 2009).…”

“…As for clarin-1, this is the first work presenting evidence that suggests a direct role in ciliogenesis for an Usher protein. Because Usher mouse models show a disruption of the hair cell bundle integrity (Lefèvre et al, 2008), most of the studies related to clarin-1 at the apical aspect of hair cells have been focused on the stereocilia Geng et al, 2009Geng et al, , 2012. Its putative role in kinocilium formation, before this work, was unexplored.…”