4 research outputs found
HOMER2, a Stereociliary Scaffolding Protein, Is Essential for Normal Hearing in Humans and Mice
<div><p>Hereditary hearing loss is a clinically and genetically heterogeneous disorder. More than 80 genes have been implicated to date, and with the advent of targeted genomic enrichment and massively parallel sequencing (TGE+MPS) the rate of novel deafness-gene identification has accelerated. Here we report a family segregating post-lingual progressive autosomal dominant non-syndromic hearing loss (ADNSHL). After first excluding plausible variants in known deafness-causing genes using TGE+MPS, we completed whole exome sequencing in three hearing-impaired family members. Only a single variant, p.Arg185Pro in <i>HOMER2</i>, segregated with the hearing-loss phenotype in the extended family. This amino acid change alters a highly conserved residue in the coiled-coil domain of HOMER2 that is essential for protein multimerization and the HOMER2-CDC42 interaction. As a scaffolding protein, HOMER2 is involved in intracellular calcium homeostasis and cytoskeletal organization. Consistent with this function, we found robust expression in stereocilia of hair cells in the murine inner ear and observed that over-expression of mutant p.Pro185 <i>HOMER2</i> mRNA causes anatomical changes of the inner ear and neuromasts in zebrafish embryos. Furthermore, mouse mutants homozygous for the targeted deletion of <i>Homer2</i> present with early-onset rapidly progressive hearing loss. These data provide compelling evidence that HOMER2 is required for normal hearing and that its sequence alteration in humans leads to ADNSHL through a dominant-negative mode of action.</p></div
Homer2 expression in P2 mouse inner ear.
<p><b>(A</b>) Staining with F-actin shows three rows of OHCs and one row of IHCs in the cochlea. (<b>B</b>) Homer2 staining in the OHCs and IHCs shows localization to stereocilia. (<b>C</b>) Merged pictures showing co-localization of Homer2 with F-actin in HC stereocilia. (<b>D</b>) Zoomed view of OHCs shows pronounced localization of Homer2 to the tips of stereocilia. Scale bar represents 10μm.</p
Pedigree, clinical data, HOMER2 mutation and protein structure.
<p><b>(A)</b> The pedigree of a five-generation family segregating progressive ADNSHL. DNA samples were obtained for 9 unaffected and 10 affected individuals. The partially filled symbol represents a two-year-old female who carries the <i>HOMER2</i> mutation but in whom a formal ABR has not been performed. Individuals who underwent TGE+MPS using either the deafness panel (OtoSCOPE) or WES are marked with an O or W, respectively. Genotypes of participating family members are shown below each symbol in single letter amino acid nomenclature: P for Proline and R for Arginine. (<b>B)</b> Age-related typical audiograms (ARTA). Binaural mean air conduction thresholds (dB HL) are presented for the ages 10–70 years. Hearing levels ranged from 0 to 120 dB depending on age and frequency; the annual threshold deterioration (ATD) was 1.2–1.6 dB/year at all frequencies. (<b>C)</b> Representative chromatograms from wild-type and mutant sequences. (<b>D)</b> Diagram of HOMER2 structure; the amino acid numbering indicates the beginning and end of the EVH1 and CC domains. The CC includes the CDC42 binding domain (CBD), Leucine Zipper-A (LZA) and Leucine Zipper-B (LZB). The position of the p.Arg185Pro mutation is shown in red.</p
Over-expression of wtRNA and P185RNA in zebrafish embryos.
<p><b>(A)</b> Otic capsule morphology in non-injected (i, n = 26), wtRNA-injected (ii, n = 26) and P185RNA-injected (iii, n = 27) embryos at 72 hpf. Scale bar represents 50μm. Embryos are mounted anterior to the left. (<b>B)</b> Comparison of otic capsule morphology between WT and mutant RNA injected zebrafish shows reduced inner ear size in mutant RNA injected larvae (p<0.001). <b>(C)</b> Hair cell kinocilia in P185RNA-injected larvae (iii) show fewer kinocilia as compared to non-injected (i) and wtRNA-injected larvae (ii). Scale bar represents 5μm. <b>(D)</b> Kinocilia count per neuromast comparison between wtRNA-injected (n = 56) and P185RNA-injected (n = 55). All data are presented as the mean ± SEM and are derived from at least triplicates (*<i>P</i> < 0.05 as compared with controls considered significant).</p