Unique residues on the H2A.Z containing nucleosome surface are important for Xenopus laevis development

Critical to vertebrate development is a complex program of events that establishes specialized tissues and organs from a single fertilized cell. Transitions in chromatin architecture, through alterations in its composition and modification markings, characterize early development. A variant of the H2A core histone, H2A.Z, is essential for development of both Drosophila and mice. We recently showed that H2A.Z is required for proper chromosome segregation. Whether H2A.Z has additional specific functions during early development remains unknown. Here we demonstrate that depletion of H2A.Z by RNA interference perturbs Xenopus laevis development at gastrulation leading to embryos with malformed, shortened trunks. Consistent with this result, whole embryo in situ hybridization indicates that endogenous expression of H2A.Z is highly enriched in the notochord. H2A.Z modifies the surface of a canonical nucleosome by creating an extended acidic patch and a metal ion-binding site stabilized by two histidine residues. To examine the significance of these specific surface regions in vivo, we investigated the consequences of overexpressing H2A.Z and mutant proteins during X. laevis development. Overexpression of H2A.Z slowed development following gastrulation. Altering the extended acidic patch of H2A.Z reversed this effect. Remarkably, modification of a single stabilizing histidine residue located on the exposed surface of an H2A.Z containing nucleosome was sufficient to disrupt normal trunk formation mimicking the effect observed by RNA interference. Taken together, these results argue that key determinants located on the surface of an H2A.Z nucleosome play an important specific role during embryonic patterning and provide a link between a chromatin structural modification and normal vertebrate development.     

WNT16 influences bone mineral density, cortical bone thickness, bone strength, and osteoporotic fracture risk

We aimed to identify genetic variants associated with cortical bone thickness (CBT) and bone mineral density (BMD) by performing two separate genome-wide association study (GWAS) meta-analyses for CBT in 3 cohorts comprising 5,878 European subjects and for BMD in 5 cohorts comprising 5,672 individuals. We then assessed selected single-nucleotide polymorphisms (SNPs) for osteoporotic fracture in 2,023 cases and 3,740 controls. Association with CBT and forearm BMD was tested for ～2.5 million SNPs in each cohort separately, and results were meta-analyzed using fixed effect meta-analysis. We identified a missense SNP (Thr>Ile; rs2707466) located in the WNT16 gene (7q31), associated with CBT (effect size of -0.11 standard deviations [SD] per C allele, P = 6.2 × 10(-9)). This SNP, as well as another nonsynonymous SNP rs2908004 (Gly>Arg), also had genome-wide significant association with forearm BMD (-0.14 SD per C allele, P = 2.3 × 10(-12), and -0.16 SD per G allele, P = 1.2 × 10(-15), respectively). Four genome-wide significant SNPs arising from BMD meta-analysis were tested for association with forearm fracture. SNP rs7776725 in FAM3C, a gene adjacent to WNT16, was associated with a genome-wide significant increased risk of forearm fracture (OR = 1.33, P = 7.3 × 10(-9)), with genome-wide suggestive signals from the two missense variants in WNT16 (rs2908004: OR = 1.22, P = 4.9 × 10(-6) and rs2707466: OR = 1.22, P = 7.2 × 10(-6)). We next generated a homozygous mouse with targeted disruption of Wnt16. Female Wnt16(-/-) mice had 27% (P<0.001) thinner cortical bones at the femur midshaft, and bone strength measures were reduced between 43%-61% (6.5 × 10(-13)相似文献