Mutations in a new member of the chromodomain gene family cause CHARGE syndrome

CHARGE syndrome is a common cause of congenital anomalies affecting several tissues in a nonrandom fashion. We report a 2.3-Mb de novo overlapping microdeletion on chromosome 8q12 identified by array comparative genomic hybridization in two individuals with CHARGE syndrome. Sequence analysis of genes located in this region detected mutations in the gene CHD7 in 10 of 17 individuals with CHARGE syndrome without microdeletions, accounting for the disease in most affected individuals.     

A complementary transposon tool kit for Drosophila melanogaster using P and piggyBac

With the availability of complete genome sequence for Drosophila melanogaster, one of the next strategic goals for fly researchers is a complete gene knockout collection. The P-element transposon, the workhorse of D. melanogaster molecular genetics, has a pronounced nonrandom insertion spectrum. It has been estimated that 87% saturation of the approximately 13,500-gene complement of D. melanogaster might require generating and analyzing up to 150,000 insertions. We describe specific improvements to the lepidopteran transposon piggyBac and the P element that enabled us to tag and disrupt genes in D. melanogaster more efficiently. We generated over 29,000 inserts resulting in 53% gene saturation and a more diverse collection of phenotypically stronger insertional alleles. We found that piggyBac has distinct global and local gene-tagging behavior from that of P elements. Notably, piggyBac excisions from the germ line are nearly always precise, piggyBac does not share chromosomal hotspots associated with P and piggyBac is more effective at gene disruption because it lacks the P bias for insertion in 5' regulatory sequences.     

Vinculin activation by talin through helical bundle conversion

Vinculin is a conserved component and an essential regulator of both cell-cell (cadherin-mediated) and cell-matrix (integrin-talin-mediated focal adhesions) junctions, and it anchors these adhesion complexes to the actin cytoskeleton by binding to talin in integrin complexes or to alpha-actinin in cadherin junctions. In its resting state, vinculin is held in a closed conformation through interactions between its head (Vh) and tail (Vt) domains. The binding of vinculin to focal adhesions requires its association with talin. Here we report the crystal structures of human vinculin in its inactive and talin-activated states. Talin binding induces marked conformational changes in Vh, creating a novel helical bundle structure, and this alteration actively displaces Vt from Vh. These results, as well as the ability of alpha-actinin to also bind to Vh and displace Vt from pre-existing Vh-Vt complexes, support a model whereby Vh functions as a domain that undergoes marked structural changes that allow vinculin to direct cytoskeletal assembly in focal adhesions and adherens junctions. Notably, talin's effects on Vh structure establish helical bundle conversion as a signalling mechanism by which proteins direct cellular responses.     

Thiamine derivatives bind messenger RNAs directly to regulate bacterial gene expression

Although proteins fulfil most of the requirements that biology has for structural and functional components such as enzymes and receptors, RNA can also serve in these capacities. For example, RNA has sufficient structural plasticity to form ribozyme and receptor elements that exhibit considerable enzymatic power and binding specificity. Moreover, these activities can be combined to create allosteric ribozymes that are modulated by effector molecules. It has also been proposed that certain messenger RNAs might use allosteric mechanisms to mediate regulatory responses depending on specific metabolites. We report here that mRNAs encoding enzymes involved in thiamine (vitamin B(1)) biosynthesis in Escherichia coli can bind thiamine or its pyrophosphate derivative without the need for protein cofactors. The mRNA-effector complex adopts a distinct structure that sequesters the ribosome-binding site and leads to a reduction in gene expression. This metabolite-sensing regulatory system provides an example of a 'riboswitch' whose evolutionary origin might pre-date the emergence of proteins.     

The harlequin mouse mutation downregulates apoptosis-inducing factor

Harlequin (Hq) mutant mice have progressive degeneration of terminally differentiated cerebellar and retinal neurons. We have identified the Hq mutation as a proviral insertion in the apoptosis-inducing factor (Aif) gene, causing about an 80% reduction in AIF expression. Mutant cerebellar granule cells are susceptible to exogenous and endogenous peroxide-mediated apoptosis, but can be rescued by AIF expression. Overexpression of AIF in wild-type granule cells further decreases peroxide-mediated cell death, suggesting that AIF serves as a free radical scavenger. In agreement, dying neurons in aged Hq mutant mice show oxidative stress. In addition, neurons damaged by oxidative stress in both the cerebellum and retina of Hq mutant mice re-enter the cell cycle before undergoing apoptosis. Our results provide a genetic model of oxidative stress-mediated neurodegeneration and demonstrate a direct connection between cell cycle re-entry and oxidative stress in the ageing central nervous system.     

Systematic screen for human disease genes in yeast

High similarity between yeast and human mitochondria allows functional genomic study of Saccharomyces cerevisiae to be used to identify human genes involved in disease. So far, 102 heritable disorders have been attributed to defects in a quarter of the known nuclear-encoded mitochondrial proteins in humans. Many mitochondrial diseases remain unexplained, however, in part because only 40-60% of the presumed 700-1,000 proteins involved in mitochondrial function and biogenesis have been identified. Here we apply a systematic functional screen using the pre-existing whole-genome pool of yeast deletion mutants to identify mitochondrial proteins. Three million measurements of strain fitness identified 466 genes whose deletions impaired mitochondrial respiration, of which 265 were new. Our approach gave higher selection than other systematic approaches, including fivefold greater selection than gene expression analysis. To apply these advantages to human disorders involving mitochondria, human orthologs were identified and linked to heritable diseases using genomic map positions.     

Low-penetrance susceptibility to breast cancer due to CHEK2(*)1100delC in noncarriers of BRCA1 or BRCA2 mutations

Mutations in BRCA1 and BRCA2 confer a high risk of breast and ovarian cancer, but account for only a small fraction of breast cancer susceptibility. To find additional genes conferring susceptibility to breast cancer, we analyzed CHEK2 (also known as CHK2), which encodes a cell-cycle checkpoint kinase that is implicated in DNA repair processes involving BRCA1 and p53 (refs 3,4,5). We show that CHEK2(*)1100delC, a truncating variant that abrogates the kinase activity, has a frequency of 1.1% in healthy individuals. However, this variant is present in 5.1% of individuals with breast cancer from 718 families that do not carry mutations in BRCA1 or BRCA2 (P = 0.00000003), including 13.5% of individuals from families with male breast cancer (P = 0.00015). We estimate that the CHEK2(*)1100delC variant results in an approximately twofold increase of breast cancer risk in women and a tenfold increase of risk in men. By contrast, the variant confers no increased cancer risk in carriers of BRCA1 or BRCA2 mutations. This suggests that the biological mechanisms underlying the elevated risk of breast cancer in CHEK2 mutation carriers are already subverted in carriers of BRCA1 or BRCA2 mutations, which is consistent with participation of the encoded proteins in the same pathway.