Differential expression of otoferlin in brain, vestibular system, immature and mature cochlea of the rat

Abstract

Mutations of the human otoferlin gene lead to an autosomal recessive nonsyndromic form of prelingual, sensorineural deafness (deafness autosomal recessive 9, DFNB9). Several studies have demonstrated expression of otoferlin in the inner ear and brain, and suggested a role of otoferlin in Ca(2+)-triggered exocytosis. So far, otoferlin expression profiles were solely based on the detection of mRNA. Here, we analysed the expression of otoferlin protein and mRNA using immunohistochemistry, in situ hybridization and RT-PCR in neonatal and mature Wistar rat tissue. In agreement with previous studies, otoferlin expression was found in the brain and in inner and vestibular hair cells. Otoferlin mRNA and protein was, however, also detected in mature outer hair cells of low-frequency processing cochlear turns and in auditory nerve fibres. In outer, inner and vestibular hair cells, otoferlin was subcellularly localized at a considerable distance from the presumed active release sites. Double-staining with the synaptic ribbon marker, C-terminal binding protein 2 (CtBP2), or the presynaptic Ca(2+)-channel, Ca(v)1.3, both assumed to mark the sites of vesicle fusion and transmitter release, did not colocalize with otoferlin expression and thus do not necessarily support a selected role of otoferlin in Ca(2+)-triggered exocytosis. The widespread distribution of otoferlin in neurons, nerve fibres and hair cells, and its subcellular distribution extending beyond the regions of synaptic vesicle fusion, i.e. coenrichment with the cytosolic Golgi matrix protein 130 (GM130) in inner hair cells or the early endosomal autoantigen 1 (EEA1) in outer hair cells support instead the idea of a more ubiquitous role of otoferlin in early/recycling endosome trans-Golgi network dynamics.

A missense mutation in the conserved C2B domain of otoferlin causes deafness in a new mouse model of DFNB9

“…OTOF protein is highly expressed in both cochlear and vestibular hair cells of rat (Schug et al, 2006) and mouse (Roux et al, 2006) inner ears, yet mice with otoferlin mutations, although deaf, appear to have normal vestibular function on the basis of behavioral assessments. Results from behavioral tests, however, cannot exclude the possiblility that normal balance is achieved by compensation from visual or proprioceptive inputs.…”

“…Auditory brainstem response (ABR) analysis demonstrates that mice homozygous for this missense mutation are profoundly deaf. Otoferlin is strongly expressed in vestibular as well as cochlear hair cells (Roux et al, 2006;Schug et al, 2006), yet mutant mice do not exhibit circling or head bobbing behaviors typical of vestibular dysfunction in mice. To directly assess receptor function, we measured vestibular-evoked potentials (VsEPs) (Jones et al, 2005), but found no evidence of vestibular deficits in deaf5/deaf5 mutant mice compared with controls.…”

Preliminary studies on differential expression of auditory functional genes in the brain after repeated blast exposures

“…The expression of otoferlin, which is known to be present in the brain and is essential for glutamate exocytosis at the auditory ribbon synapse and reported to be defective in a recessive form of human deafness, showed significant decrease in the hippocampus of mice exposed to repeated blasts [19][20][40][41][42]. In contrast, otoancorin, another hearing-related gene defective in autosomal recessive deafness and known to mediate the contact between the apical surface of sensory epithelial cells and acellular gels of the inner ear and the tectorial and otoconial membranes for proper auditory processing, showed significant increase in the hippocampus after repeated blast exposures [21,43].…”

“…Cadherin and protocadherin mutations were linked to digenic inheritance of deafness and have specific functional roles in noise-induced hearing loss [13][14][16][17]. Other groups of proteins involved in deafness are otoferlin and otoancorin, which are also reported to have major roles in auditory functions, including central auditory processing [18][19][20][21]. Another large class of molecules involved in auditory signaling is centered on the calcium regulating proteins, which are known to have broad functions in age-and noise-related hearing loss or protection [18,[22][23][24][25][26].…”

The otoferlin interactome in neurosensory hair cells: Significance for synaptic vesicle release and trans-Golgi network (Review)

“…One first indication of such additional functions was the demonstration of its expression in a widened pattern, including the brain (25), the vestibular system, neurons and nerve fibers. Also, apart from its presence in cochlear inner hair cells, otoferlin was found to be present in mature outer hair cells responsible for low-frequency processing (30). Its subcellular distribution beyond regions of synaptic vesicle fusion and its association with Golgi markers suggested a more ubiquitous role.…”