Wnt signaling pathway involvement in genotypic and phenotypic variations in Waardenburg syndrome type 2 with MITF mutations.

Mutation in the gene encoding microphthalmia-associated transcription factor (MITF) lead to Waardenburg syndrome 2 (WS2), an autosomal dominantly inherited syndrome with auditory-pigmentary abnormalities, which is clinically and genetically heterogeneous. Haploinsufficiency may be the underlying mechanism for WS2. However, the mechanisms explaining the genotypic and phenotypic variations in WS2 caused by MITF mutations are unclear. A previous study revealed that MITF interacts with LEF-1, an important factor in the Wnt signaling pathway, to regulate its own transcription through LEF-1-binding sites on the MITF promoter. In this study, four different WS2-associated MITF mutations (p.R217I, p.R217G, p.R255X, p.R217del) that are associated with highly variable clinical features were chosen. According to the results, LEF-1 can activate the expression of MITF on its own, but MITF proteins inhibited the activation. This inhibition weakens when the dosage of MITF is reduced. Except for p.R217I, p.R255X, p.R217G, and p.R217del lose the ability to activate TYR completely and do not inhibit the LEF-1-mediated activation of the MITF-M promoter, and the haploinsufficiency created by mutant MITF can be overcome; correspondingly, the mutants' associated phenotypes are less severe than that of p.R217I. The dominant negative of p.R217del made it have a second-most severe phenotype. This study's data imply that MITF has a negative feedback loop of regulation to stabilize MITF gene dosage that involves the Wnt signaling pathway and that the interaction of MITF mutants with this pathway drives the genotypic and phenotypic differences observed in Waardenburg syndrome type 2 associated with MITF mutations.

Functional analysis of a SOX10 gene mutation associated with Waardenburg syndrome II.

Waardenburg syndrome (WS) is an autosomal dominant inherited non-syndromic type of hereditary hearing loss characterized by varying combinations of sensorineural hearing loss and abnormal pigmentation of the hair, skin, and inner ear. WS is classified into four subtypes (WS1-WS4) based on additional symptoms. WS2 is characterized by the absence of additional symptoms. Recently, we identified a SOX10 missense mutation c.422T > C (p.L141P) associated with WS2. We performed functional assays and found the mutant loses DNA-binding capacity, shows aberrant cytoplasmic and nuclear localization, and fails to interact with PAX3. Therefore, the mutant cannot transactivate the MITF promoter effectively, inhibiting melanin synthesis and leading to WS2. Our study confirmed haploinsufficiency as the underlying pathogenesis for WS2.

Digenic mutations involving both the BSND and GJB2 genes detected in Bartter syndrome type IV.

Bartter syndrome type IV, characterized by salt-losing nephropathies and sensorineural deafness, is caused by mutations of BSND or simultaneous mutations of both CLCNKA and CLCNKB. GJB2 is the primary causative gene for non-syndromic sensorineural deafness and associated with several syndromic sensorineural deafness. Owing to the rarity of Bartter syndrome, only a few mutations have been reported in the abovementioned causative genes. To investigate the underlying mutations in a Chinese patient with Bartter syndrome type IV, genetic analysis of BSND, CLCNKA, CLCNKB and GJB2 were performed by polymerase chain reaction and direct sequencing. Finally, double homozygous mutations c.22C > T (p.Arg8Trp) and c.127G > A (Val43Ile) were detected in exon 1 of BSND. Intriguingly, compound heterozygous mutations c.235delC (p.Leu79CysfsX3) and c.109G > A (p.Val37Ile) were also revealed in exon 2 of GJB2 in the same patient. No pathogenic mutations were found in CLCNKA and CLCNKB. Our results indicated that the homozygous mutation c.22C > T was the key genetic reason for the proband, and a digenic effect of BSND and GJB2 might contributed to sensorineural deafness. To our knowledge, it was the first report showing that the GJB2 gene mutations were detected in Bartter syndrome.

Exome sequencing identifies POU4F3 as the causative gene for a large Chinese family with non-syndromic hearing loss.

Hearing impairment, or deafness (in its most severe form), is one of the most common human sensory disorders. There have been several reports of autosomal dominant mutations in the POU4F3 gene, which is associated with non-syndromic hearing loss. In this study, we identified a novel heterozygous mutation (c.602delT, p.L201fs) in the gene POU4F3 by taking advantage of whole-exome sequencing, which was validated by Sanger sequencing and completely co-segregated within a large hearing impaired Chinese family. We have focused on this pedigree since 2002, and we have mapped a deafness locus named DFNA42 (which has been renamed DFNA52, OMIM entry 607683) via a genome-wide scan. Furthermore, we analyzed this mutational variant and found that it was located at the beginning of the first functional domain of POU4F3, which could theoretically impair the function of POU4F3. We have identified a novel frameshift mutation in the POU4F3 gene. Further functional studies of variants of this specific gene are needed to illustrate the pathogenic mechanism(s) that underlie hearing impairment.

Identification and functional analysis of a novel mutation in the SOX10 gene associated with Waardenburg syndrome type IV.

Waardenburg syndrome type IV (WS4) is a rare genetic disorder, characterized by auditory-pigmentary abnormalities and Hirschsprung disease. Mutations of the EDNRB gene, EDN3 gene, or SOX10 gene are responsible for WS4. In the present study, we reported a case of a Chinese patient with clinical features of WS4. In addition, the three genes mentioned above were sequenced in order to identify whether mutations are responsible for the case. We revealed a novel nonsense mutation, c.1063C>T (p.Q355*), in the last coding exon of SOX10. The same mutation was not found in three unaffected family members or 100 unrelated controls. Then, the function and mechanism of the mutation were investigated in vitro. We found both wild-type (WT) and mutant SOX10 p.Q355* were detected at the expected size and their expression levels are equivalent. The mutant protein also localized in the nucleus and retained the DNA-binding activity as WT counterpart; however, it lost its transactivation capability on the MITF promoter and acted as a dominant-negative repressor impairing function of the WT SOX10.

[Screening and identification interaction proteins of connexin 30].

OBJECTIVE: To explore interaction proteins affect functions of connexin 30 (Cx30) by screening and identification interaction proteins of Cx30. METHODS: The fusion expression vecto of CX30-C-terminal functional domain-pGEX-4T-2-GST was constructed, and then, fusion protein and GST were purified. They were incubated with the proteins of the foetus brain tissue disruption to pull down interaction proteins. The interaction proteins were separated by SDS-PAGE. Differential straps were cut to enzymolysis to prepare for mass chromatographic analysis, and then to index and screen interaction proteins in NCBInr database. The interaction proteins were identified by immunolocalization. RESULTS: The four interaction proteins of Cx30 were screened in the foetus brain tissue, as follow, Keratin 16, Camk2b, Tubulin beta-3 and alpha-tubulin. Cx30 was proved to coexist with Keratin 16 and Tubulin beta-3. CONCLUSIONS: Keratin 16, Camk2b, Tubulin beta-3 and alpha-tubulin are the interaction proteins of Cx30. The interaction proteins affect the assembly, intracellular transport, and channel switch of Cx30.

[An analysis of a large hereditary postlingually deaf families and detecting mutation of the deafness genes].

OBJECTIVE: To make a further exploration of the mutation frequence of Chinese genetic deafness and make clear if the genetic deafness genealogy that we collected recently was resulted from the mutation of the deafness genes which had been cloned. METHOD: We made regular otologic examination, hearing test and physical examination among the members of this genealogy, and also inspected the mutation of seven autosomal domiant deafness genes, HDIAI,GJB2, GJB3, DFNA5, a-tectorin(resulting in two types of genetic deafness, DFNA8 and DFNA12), MYO7A,POU4F3, with PCR-Sequencing method in this genealogy. RESULT: 1. The analysis of hereditary mode: There were forty-seven persons collected in five generations of this genealogy, and eighteen persons of them were deafness. It accorded with autosomal dominant inheritance from the pedigree. 2. The clinic feature: All patients with deafness were postlingual deafness. Their hearing decreased onset between sixteen to thirty years old, and the deafness was binaural symmetrical, progressive sensorineural and without other systems abnormity. 3. Analysis of mutation detection: We found two nucleotides changes in CX26 genes, A341G and GC257-258CG, and one changed nucleotide in POU4F3 gene,T90C. But we didn't think the changed nucleotides caused deafness after we analysed them. No mutation was found in other five genes. CONCLUSION: The possibility that the deafness of this genealogy was resulted from the cloned gene is relatively small. Now, We are scanning the whole gene groups and making linkage analysis on this pedigree, it is most probably to orientate a new deafness gene position.