Mutations in connexin31 underlie recessive as well as dominant non-syndromic hearing loss

Abstract

Mutations in the GJB3 gene encoding connexin31 (Cx31) can cause a dominant non-syndromic form of hearing loss (DFNA2). To determine whether mutations at this locus can also cause recessive non-syndromic deafness, we screened 25 Chinese families with recessive deafness and identified in two families affected individuals who were compound heterozygotes for Cx31 mutations. The three affected individuals in the two families were born to non-consanguineous parents and had an early onset bilateral sensorineural hearing loss. In both families, differing SSCP patterns were observed in affected and unaffected individuals. Sequence analysis in both families demonstrated an in-frame 3 bp deletion (423-425delATT) in one allele, which leads to the loss of an isoleucine residue at codon 141, and a 423A-->G transversion in the other allele, which creates an Ile-->Val substitution at codon 141 (I141V). Neither of these two mutations was detected in DNA from 100 unrelated control subjects. The altered isoleucine residue lies within the third conserved alpha-helical transmembrane domain (M3), which is critical for the formation of the wall of the gap junction pore. Both the deletion of the isoleucine residue 141 and its substitution to valine in the two families could alter the structure of M3, and impair the function of the gap junction. The present data demonstrate that, like mutations in connexin26, mutations in Cx31 can lead to both recessive and dominant forms of non-syndromic deafness.

Cx31 is assembled and trafficked to cell surface by ER-Golgi pathway and degraded by proteasomal or lysosomal pathways

“…To analyze the Cx31 degradation pathway, HeLa cells stably expressing Cx31 were incubated with different drugs (20 µM ALLN (proteasomal inhibitor, Sigma), 200 µM leupeptin (Leu) (Sigma), 10 mM NH 4 Cl, 100 µM CLQ (Sigma), 25 µM trans-epoxysaccinyl-Lleucylamide-(4-guanidino) butane (E-64) (Leu, NH 4 Cl, CLQ, E-64 are all lysosomal inhibitors), and 20 µg/ml cycloheximide (CHX), or some combination of these drugs) for 6 h. HeLa cells were washed with PBS and harvested by scraping. The cells were then concentrated by centrifugation (1300 g, 5 min) and lysed with RIPA.…”

“…6 A). To explore the pathway of Cx31 degradation, HeLa cells stably expressing Cx31/myc were treated with different drugs for 4 h. These drugs included ALLN to inhibit proteasomal activity, CHX to inhibit protein synthesis, as well as CLQ, E64, NH 4 Cl and Leu to inhibit lysosomal the cytoplasm after HeLa cells were treated with ALLN, CLQ, NH 4 Cl, or E-64, while little expression was found in untreated HeLa cells. The quantity of Cx31 reduced in CHX treated HeLa cells compared to untreated ones (Fig.…”

“…Mutations in Cx31 would cause erythrokeratodermia variabilis (EKV), hearing impairment, and peripheral neuropathy, respectively [4][5][6][7]. However, the mechanism of Cx31 in the pathogenesis of these diseases remains unclear.…”

A large deletion including most of GJB6 in recessive non syndromic deafness: a digenic effect?

“…9 Mutations in GJB3 are responsible for dominant or recessive deafness. 10,11 Finally, one mutation in GJB6 causes hearing loss by a dominant negative effect. 12 As the two genes GJB6 and GJB2 are lying *35 kb apart, they both define the DFNA3 locus.…”

Early embryonic expression of ion channels and pumps in chick and Xenopus development

“…Cx31, which is involved in the function of the ear (Liu et al, 2000), is expressed in the posterior margin of the area pellucida in the chick embryo at st. 4 ϩ (Fig. 6A), similar to some of the BMP genes.…”