A missense mutation in DCDC2 causes human recessive deafness DFNB66, likely by interfering with sensory hair cell and supporting cell cilia length regulation

Abstract

Hearing loss is the most common sensory deficit in humans. We show that a point mutation in DCDC2 (DCDC2a), a member of doublecortin domain-containing protein superfamily, causes non-syndromic recessive deafness DFNB66 in a Tunisian family. Using immunofluorescence on rat inner ear neuroepithelia, DCDC2a was found to localize to the kinocilia of sensory hair cells and the primary cilia of nonsensory supporting cells. DCDC2a fluorescence is distributed along the length of the kinocilium with increased density toward the tip. DCDC2a-GFP overexpression in non-polarized COS7 cells induces the formation of long microtubule-based cytosolic cables suggesting a role in microtubule formation and stabilization. Deafness mutant DCDC2a expression in hair cells and supporting cells causes cilium structural defects, such as cilium branching, and up to a 3-fold increase in length ratios. In zebrafish, the ortholog dcdc2b was found to be essential for hair cell development, survival and function. Our results reveal DCDC2a to be a deafness gene and a player in hair cell kinocilia and supporting cell primary cilia length regulation likely via its role in microtubule formation and stabilization.

Understanding Language from a Genomic Perspective

“…As well as respiratory symptoms characteristic of primary ciliary dyskinesia, some individuals had additional cilia-related abnormalities, including infertility, and disrupted left-right body asymmetry, comparable to those observed in animal models (167). Strikingly, a second dyslexia candidate gene, DCDC2, was found to be essential to ciliary function following discovery of a homozygous missense variant cosegregating with congenital deafness in a consanguineous family (53). Expression of the deafness-associated variant in rat inner ear organotypic cultures, and gene knockdown in zebrafish, confirmed the ciliary role (53,141).…”

Hearing Assessment in Zebrafish During the First Week Postfertilization

“…The microphonic potential method has been successfully applied to wild-type, transgenic, and mutant/morphant zebrafish embryos and young larvae and has become a quick powerful tool to assess hair cell function in the zebrafish model. [3][4][5]20,45,46 Moreover, we chose low stimulus frequencies from 20 to 400 Hz because the inner ears of zebrafish of 1-week old or younger are only ''motion sensitive'' through a direct stimulus pathway 55 and are not yet pressure sensitive until the initial formation of the Weberian ossicles at about 20 dpf. 56 Weberian ossicles are auditory accessories known to increase the auditory sensitivity at high frequencies.…”

“…[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.…”