HSF4 is involved in DNA damage repair through regulation of Rad51.

Heat shock factor protein 4 (HSF4) is expressed exclusively in the ocular lens and plays a critical role in the lens formation and differentiation. Mutations in the HSF4 gene lead to congenital and senile cataract. However, the molecular mechanisms causing this disease have not been well characterized. DNA damage in lens is a crucial risk factor in senile cataract formation, and its timely repair is essential for maintaining the lens' transparency. Our study firstly found evidence that HSF4 contributes to the repair of DNA strand breaks. Yet, this does not occur with cataract causative mutations in HSF4. We verify that DNA damage repair is mediated by the binding of HSF4 to a heat shock element in the Rad51 promoter, a gene which assists in the homologous recombination (HR) repair of DNA strand breaks. HSF4 up-regulates Rad51 expression while mutations in HSF4 fail, and DNA does not get repaired. Camptothecin, which interrupts the regulation of Rad51 by HSF4, also affects DNA damage repair. Additionally, with HSF4 knockdown in the lens of Zebrafish, DNA damage was observed and the protein level of Rad51 was significantly lower. Our study presents the first evidence demonstrating that HSF4 plays a role in DNA damage repair and may contribute a better understanding of congenital cataract formation.

Identification of compound heterozygous mutations in GNPTG in three siblings of a Chinese family with mucolipidosis type III gamma.

Mucolipidosis III gamma is an autosomal recessive disorder with defective phosphorylation and trafficking of lysosomal enzymes. In a Chinese family with three siblings, linkage analysis revealed positive linkage of the family to GNPTG. Direct DNA sequence analysis identified two novel compound heterozygous mutations, c.471delC in exon 7 and IVS4-1G>C, in three patients. The two mutations cause frameshift and abnormal splicing, respectively, and represent the first series of GNPTG mutations in the Chinese population.

Cataract mutation P20S of alphaB-crystallin impairs chaperone activity of alphaA-crystallin and induces apoptosis of human lens epithelial cells.

Cataract is a common cause of childhood blindness worldwide. alpha-crystallin, which is comprised of two homologous subunits, alphaA- and alphaB-crystallin, plays a key role in the maintenance of lens transparency. Recently, we have identified a missense mutation in alphaB-crystallin that changes the proline residue at codon 20 to a serine residue (P20S) in a large Chinese family with autosomal dominant posterior polar congenital cataract. To explore the molecular mechanism by which the P20S mutation causes cataract, we examined the quaternary structure, subunit exchange and chaperone activity of the reconstituted heteroaggregates of alpha-crystallins containing wild type (WT) alphaA in combination with either WT-alphaB- or mutant alphaB-crystallin, respectively. Compared with heteroaggregates of WT-alphaA and WT-alphaB, heteroaggregates containing WT-alphaA and mutant alphaB showed nearly the same molecular mass, but the subunit-exchange rate and chaperone activity were decreased markedly. In human lens epithelial cells, unlike WT-alphaB-crystallin, the P20S mutant protein showed abnormal nuclear localization, and unusual ability to trigger apoptosis. These results suggest that the changes in the structure and function of the alpha-crystallin complex and cytotoxicity are vital factors in the pathogenesis of congenital cataract linked to the P20S mutation in the alphaB-crystallin.

Identification of a genetic locus for autosomal dominant disseminated superficial actinic porokeratosis on chromosome 1p31.3-p31.1.

Disseminated superficial actinic porokeratosis (DSAP) is a chronic autosomal dominant cutaneous disorder with high genetic heterogeneity. Two genetic loci for DSAP were identified, but no specific genes were reported to date. The pathogenic mechanism of this disorder remains to be elucidated. In this study, a large, five-generation Chinese family with DSAP was genetically characterized. Two known DSAP loci, DSAP1 and DSAP2, two DSAP candidate genes (SART3 and SSH1), one DSP-linked locus and one PPPD-linked locus were first excluded in the family. The family was then characterized by genome-wide linkage analysis and a new DSAP locus was identified on chromosome 1p31.3-p31.1 with a maximum two-point LOD score of 5.09 with marker D1S2897 (theta = 0). Fine mapping showed that the disease gene was located within an 8.2 cM or 11.9 Mb region between markers D1S438 and D1S464. This is the third locus identified for DSAP (DSAP3). Eight candidate genes including GNG12, IL12RB2, ITGB3BP, DNAJ6, PIN1L, GADD45A, RPE65 and NEGR1 were sequenced, but found to be negative for functional sequence variants. Further mutational analysis of the candidate genes in the region will identify the specific gene for DSAP, which will provide insights into the pathogenesis of DSAP.

[Advances in the studies on the molecular and genetic aspects of epilepsy].

Epilepsy is one of the most common and debilitating neurological diseases that affects more than 40 million people worldwide. Genetic factors contribute to the pathogenesis of epilepsy. Molecular genetic studies have identified 15 disease-causing genes for epilepsy. The majority of the genes encode ion channels, including voltage-gated potassium channels KCNQ2 and KCNQ3, sodium channels SCN1A, SCN2A, and SCN1B, chloride channels CLCN2, and ligand-gated ion channels CHRNA4, CHRNB2, GABRG2, and GABRA1. Interestingly, non-ion channel genes have also been identified as epilepsy genes, and these genes include G-protein-coupled receptor MASS1/VLGR1, GM3 synthase, and proteins with unknown functions such as LGI1, NHLRC1, and EFHC1. These studies make genetic testing possible in some patients, and further characterization of the identified epilepsy genes may lead to the development of new drugs and new treatments for patients with epilepsy.

Identification and molecular characterization of two novel mutations in COL1A2 in two Chinese families with osteogenesis imperfecta.

Osteogenesis imperfecta (OI, also known as brittle bone disease) is caused mostly by mutations in two type I collagen genes, COL1A1 and COL1A2 encoding the pro-α1 (I) and pro-α2 (I) chains of type I collagen, respectively. Two Chinese families with autosomal dominant OI were identified and characterized. Linkage analysis revealed linkage of both families to COL1A2 on chromosome 7q21.3-q22.1. Mutational analysis was carried out using direct DNA sequence analysis. Two novel missense mutations, c.3350A>G and c.3305G>C, were identified in exon 49 of COL1A2 in the two families, respectively. The c.3305G>C mutation resulted in substitution of a glycine residue (G) by an alanine residue (A) at codon 1102 (p.G1102A), which was found to be mutated into serine (S), argine (R), aspartic acid (D), or valine (V) in other families. The c.3350A>G variant may be a de novo mutation resulting in p.Y1117C. Both mutations co-segregated with OI in respective families, and were not found in 100 normal controls. The G1102 and Y1117 residues were evolutionarily highly conserved from zebrafish to humans. Mutational analysis did not identify any mutation in the COX-2 gene (a modifier gene of OI). This study identifies two novel mutations p.G1102A and p.Y1117C that cause OI, significantly expands the spectrum of COL1A2 mutations causing OI, and has a significant implication in prenatal diagnosis of OI.