FAM65B is a membrane-associated protein of hair cell stereocilia required for hearing

Abstract

In a large consanguineous Turkish kindred with recessive nonsyndromic, prelingual, profound hearing loss, we identified in the gene FAM65B (MIM611410) a splice site mutation (c.102-1G>A) that perfectly cosegregates with the phenotype in the family. The mutation leads to exon skipping and deletion of 52-amino acid residues of a PX membrane localization domain. FAM65B is known to be involved in myotube formation and in regulation of cell adhesion, polarization, and migration. We show that wild-type Fam65b is expressed during embryonic and postnatal development stages in murine cochlea, and that the protein localizes to the plasma membranes of the stereocilia of inner and outer hair cells of the inner ear. The wild-type protein targets the plasma membrane, whereas the mutant protein accumulates in cytoplasmic inclusion bodies and does not reach the membrane. In zebrafish, knockdown of fam65b leads to significant reduction of numbers of saccular hair cells and neuromasts and to hearing loss. We conclude that FAM65B is a plasma membrane-associated protein of hair cell stereocilia that is essential for hearing.deafness | whole-exome sequencing | congenital | Mendelian disorder | sensorineural H earing loss is the most common sensory problem, affecting approximately 1 in 500 newborns. Most cases are the consequence of mutations in single genes with specific functions in the inner ear (1) (http://hereditaryhearingloss.org). Hearing depends on the ability of the inner ear to convert acoustic waves into electrical signals. This process originates in the stereocilia, actin-rich structures that project from the apical pole of cochlear hair cells and are interconnected in the shape of a staircase to form the hair bundle. Most of the ∼50 hair-bundle proteins identified so far are the products of genes that when mutated lead to hearing loss (2). Thus, the genetic approach has played a major role in elucidating the molecular components of normal hearing.Here we present Family With Sequence Similarity 65, Member B (FAM65B, MIM611410) as a previously unrecognized, plasma membrane-associated protein of hair cell stereocilia. The critical role of FAM65B in human hearing was revealed by genetic analysis of a large family with hereditary deafness. In the zebrafish, knocking down the ortholog of FAM65B led to sensorineural hearing loss. Results A Splice Site Mutation in FAM65B Causes Profound SensorineuralHearing Loss in a Turkish Family. In a large consanguineous kindred of Turkish origin (Fig. 1A), six affected individuals had symmetric profound sensorineural hearing loss (Fig. 1B). Anamnestic evaluation and audiograms indicated congenital/prelingual onset hearing loss in all affected individuals. Available audiograms do not suggest progression of hearing loss. Transient evoked otoacoustic emissions and acoustic reflexes were negative in all affected members of the family. Auditory brainstem responses were absent as well. Affected individuals had neither delay in gross motor development nor balance problems, vertigo, dizziness, or n...

Front Signal-Dependent Accumulation of RHOA Inhibitor FAM65B at Leading Edges Polarizes Neutrophils

“…As members of this family are broadly expressed in many tissues and cell types, we anticipate that this family of proteins will have broad physiological and pathophysiological functions. Indeed, a mutation in the human FAM65B gene has recently been associated with hearing loss (Diaz-Horta et al, 2014). Future studies are needed to determine whether the phenotype is related to RHOA regulation.…”

Hearing Assessment in Zebrafish During the First Week Postfertilization

“…[1][2][3][4][5][6][7] In addition, the lateral line of zebrafish is externally exposed, which makes lateral line hair cells good candidates for experimental manipulations. Furthermore, external fertilization and optically transparent embryos allow the inner ear of zebrafish embryos to be easily accessible for live imaging and physiological recording.…”

“…1,2,[8][9][10][11] Overall, these advantages of the zebrafish make it an ideal and convenient model for research on inner ear hair cell death and regeneration, drug screens for ototoxins and otoprotectants, and discovery of new genes for sensorineural deafness. [3][4][5][12][13][14][15][16] Several studies have reported important developmental stages of morphology of the zebrafish inner ear. At 16 hours postfertilization (hpf), the otic vesicle of zebrafish starts to form, and at about 19 hpf, two tiny otoliths become visible at the anterior and posterior ends of the otic vesicle.…”

“…4,5,20,[22][23][24][25] The GFP fluorescent marker facilitates morphological observations of live hair cells and quantification of hair cells in zebrafish embryos/larvae. To further establish this transgenic zebrafish as a model for hearing disorders, there is a need to determine if this transgenic zebrafish has normal hearing like wild-type zebrafish.…”

RHO binding to FAM65A regulates Golgi reorientation during cell migration

“…First, although FAM65A only associates with active RHO proteins, interaction of FAM65B with RHOA seems to be constitutive (Rougerie et al, 2013;Gao et al, 2015). Second, FAM65A and FAM65B seem to localise differently within the cell, with FAM65B being primarily localised to the plasma membrane (Diaz-Horta et al, 2014;Gao et al, 2015), as opposed to the Golgi and cytoplasmic punctae containing FAM65A. Nevertheless, we have observed that loss of FAM65A can trigger RHO hyper-activation (Fig.…”