Project description:Inverted duplications are a common type of copy number variation (CNV) in germline and somatic genomes. Large duplications that include many genes can lead to both neurodevelopmental phenotypes in children and gene amplifications in tumors. There are several models for inverted duplication formation, most of which include a dicentric chromosome intermediate followed by breakage-fusion-bridge (BFB) cycles, but the mechanisms that give rise to the inverted dicentric chromosome in most inverted duplications remain unknown. Here we have combined high-resolution array CGH, custom sequence capture, next-generation sequencing, and long-range PCR to analyze the breakpoints of 50 nonrecurrent inverted duplications in patients with intellectual disability, autism, and congenital anomalies. Sequence analysis of breakpoint junctions reveals a normal-copy disomic spacer between inverted and non-inverted copies of the duplication. Further, short inverted repeats are present at the boundary of the disomic spacer and the inverted duplication. These data support a mechanism of inverted duplication formation whereby a chromosome with a double-strand break intrastrand pairs with itself to form a “hairpin” intermediate that, after DNA replication, produces a dicentric inverted chromosome with a disomic spacer corresponding to the site of the hairpin. We also find evidence of short insertions and inversions at inverted duplication junctions, consistent with a DNA replication-based CNV mechanism. This process can give rise to inverted duplications adjacent to terminal deletions, inverted duplications juxtaposed to translocations, and inverted duplication ring chromosomes
Project description:Inverted duplications are a common type of copy number variation (CNV) in germline and somatic genomes. Large duplications that include many genes can lead to both neurodevelopmental phenotypes in children and gene amplifications in tumors. There are several models for inverted duplication formation, most of which include a dicentric chromosome intermediate followed by breakage-fusion-bridge (BFB) cycles, but the mechanisms that give rise to the inverted dicentric chromosome in most inverted duplications remain unknown. Here we have combined high-resolution array CGH, custom sequence capture, next-generation sequencing, and long-range PCR to analyze the breakpoints of 50 nonrecurrent inverted duplications in patients with intellectual disability, autism, and congenital anomalies. Sequence analysis of breakpoint junctions reveals a normal-copy disomic spacer between inverted and non-inverted copies of the duplication. Further, short inverted repeats are present at the boundary of the disomic spacer and the inverted duplication. These data support a mechanism of inverted duplication formation whereby a chromosome with a double-strand break intrastrand pairs with itself to form a “hairpin” intermediate that, after DNA replication, produces a dicentric inverted chromosome with a disomic spacer corresponding to the site of the hairpin. We also find evidence of short insertions and inversions at inverted duplication junctions, consistent with a DNA replication-based CNV mechanism. This process can give rise to inverted duplications adjacent to terminal deletions, inverted duplications juxtaposed to translocations, and inverted duplication ring chromosomes High resolution array CGH; two-color experiment, clinical patient vs. normal control gDNA; sex mis-matched
Project description:We report here that duplications of 15 kb or more are common in the genome of the social amoeba Dictyostelium discoideum. Most of the axenic "workhorse" strains Ax2 and Ax3/4 obtained from different laboratories can be expected to carry new duplications. The auxotrophic strains DH1 and JH10 also bear previously unreported duplications. Strain Ax3/4 is known to carry a large duplication on chromosome 2 and the domain boundary of this structure shows evidence of further instability; we find a further variable duplication on chromosome 5. These duplications are lacking in Ax2, which has instead a small duplication on chromosome 1. Stocks of the type isolate NC4 are similarly variable, though we have identified some approximating the assumed ancestral genotype. More recent wild-type isolates are almost without duplications, but we can identify small deletions or regions of high divergence, possibly reflecting responses to local selective pressures. Duplications are scattered through most of the genome, and can be stable enough to reconstruct genealogies spanning decades of the history of the NC4 lineage. The expression level of many duplicated genes is increased with dosage, but for others it appears that some form of dosage compensation occurs.
Project description:Numerous DNA double-strand breaks (DSBs) arise during meiosis to initiate homologous recombination. These DSBs are usually repaired faithfully, but here we uncover a new type of mutational event in which deletions form via joining of ends from two closely-spaced DSBs (double cuts) within a single hotspot or at adjacent hotspots on the same or different chromatids. Deletions occur in normal meiosis but are much more frequent when DSB formation is dysregulated in the absence of the ATM kinase. Events between chromosome homologs point to multi-chromatid damage and aborted gap repair. Some deletions contain DNA from other hotspots, indicating that double cutting at distant sites creates substrates for insertional mutagenesis. End joining at double cuts can also yield tandem duplications or extrachromosomal circles. Our findings highlight the importance of DSB regulation and reveal a previously hidden potential for meiotic mutagenesis that is likely to affect human health and genome evolution.
Project description:Deletions and duplications in mitochondrial DNA (mtDNA) cause mitochondrial disease and accumulate in conditions such as cancer and age-related disorders, but validated high-throughput methodology that can readily detect and discriminate between these two types of events is lacking. Here we present MitoSAlt, a computational method for accurate identification, quantification and visualization of mtDNA deletions and duplications from whole genome, whole exome or transcriptome sequencing data. MitoSAlt was tested on simulated sequencing reads and human patient samples with single deletions and duplications to verify its accuracy. Application to mouse models of mtDNA maintenance disease further demonstrated the ability to detect deletions and duplications even at low levels of heteroplasmy. MitoSAlt paves the way for simple and reliable determination of mtDNA deletions and duplications across a wide range of relevant conditions and available sequencing datasets.
 
Project description:Gene duplication and deletion are pivotal processes shaping the structural and functional repertoire of genomes, with implications for disease, adaptation and evolution. We employed an experimental evolution framework partnered with high-throughput genomics to assess the molecular and transcriptional characteristics of novel gene copy-number variants (CNVs) in Caenorhabditis elegans populations subjected to varying intensity of selection. Here, we report a direct spontaneous genome-wide rate of gene duplication of 2.9 × 10-5 /gene/generation in C. elegans, the highest for any species to date. The increase in average transcript abundance of new duplicates arising under minimal selection is significantly greater than two-fold compared to single-copies of the same gene, suggesting that genes in segmental duplications are frequently overactive at inception. The average increase in transcriptional activity of gene duplicates is greater in MA lines that passed through single individual bottlenecks than in MA lines with larger population bottlenecks. Furthermore, there is an inverse relationship between the ancestral transcription levels of newly originating gene duplicates and population size, with duplicate copies of highly expressed genes less likely to accumulate in larger populations. The results demonstrate that there is a fitness cost of superfluous gene expression and purifying selection against new gene duplicates. However, on average, duplications also provide a significant increase in gene expression that can facilitate adaptation to novel environmental challenges.
Project description:This study centered on using a custom made Nimblegen aCGH chip that targeted all segmental duplications in the canine genome to identify associated CNVs. A total of 19 hybridizations were performed in a panel of diverse dogs and a single wolf.
Project description:This study centered on using a custom made Nimblegen aCGH chip that targeted all segmental duplications in the canine genome to identify associated CNVs. A total of 19 hybridizations were performed in a panel of diverse dogs and a single wolf. Using computational approaches all segmental duplications were identified in the canFam2 genome of the dog. A custom aCGH chip was then built that densely interrogated these segmental duplications for CNVs in a panel of diverse dog breeds and a single wolf.