Dataset Information

Dynamics and processes of copy number instability in human gamma-globin genes.

ABSTRACT: Copy number variation in the human genome is prevalent but relatively little is known about the dynamics of DNA rearrangement. We therefore used the duplicated gamma-globin genes as a simple system to explore de novo copy number changes. Rearrangements that changed gene number were seen in both germline and somatic DNA, and mainly arose by unequal sister chromatid exchange between homologous sequences, with evidence from recurrent mosaic rearrangements that many, if not all, of these events in sperm arise before meiosis. Unequal exchange frequencies are apparently controlled primarily by the degree of sequence identity shared by the duplicate genes, leading to substantial variation between haplotypes in copy number instability. Additional, more complex rearrangements generated by mechanisms not involving homologous recombination, and in some cases showing DNA transfer between chromosomes, were also detected but were rare. Sequence changes were also seen in gamma-globin DNA molecules, with strong evidence that some were genuine de novo base substitutions. They were present in sperm at a frequency far higher than predicted from current estimates of germline mutation rates, raising interesting questions about base mutation dynamics in the male germline.

SUBMITTER: Neumann R

PROVIDER: S-EPMC2889564 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature

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Dynamics and processes of copy number instability in human gamma-globin genes.

Neumann Rita R Lawson Victoria E VE Jeffreys Alec J AJ

Proceedings of the National Academy of Sciences of the United States of America 20100419 18

Copy number variation in the human genome is prevalent but relatively little is known about the dynamics of DNA rearrangement. We therefore used the duplicated gamma-globin genes as a simple system to explore de novo copy number changes. Rearrangements that changed gene number were seen in both germline and somatic DNA, and mainly arose by unequal sister chromatid exchange between homologous sequences, with evidence from recurrent mosaic rearrangements that many, if not all, of these events in s ...[more]

PMID: 20404158

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Project description:Recent large-scale genomic studies within human populations have identified numerous genomic regions as copy number variant (CNV). As these CNV regions often overlap coding regions of the genome, large lists of potentially copy number polymorphic genes have been produced that are candidates for disease association. Most of the current data regarding normal genic variation, however, has been generated using BAC or SNP microarrays, which lack precision especially with respect to exons. To address this, we assessed 2,790 candidate CNV genes defined from available studies in nine well-characterized HapMap individuals by designing a customized oligonucleotide microarray targeted specifically to exons. Using exon array comparative genomic hybridization (aCGH), we detected 255 (9%) of the candidates as true CNVs including 134 with evidence of variation over the entire gene. Individuals differed in copy number from the control by an average of 100 gene loci. Both partial- and whole-gene CNVs were strongly associated with segmental duplications (55 and 71%, respectively) as well as regions of positive selection. We confirmed 37% of the whole-gene CNVs using the fosmid end sequence pair (ESP) structural variation map for these same individuals. If we modify the end sequence pair mapping strategy to include low-sequence identity ESPs (98-99.5%) and ESPs with an everted orientation, we can capture 82% of the missed genes leading to more complete ascertainment of structural variation within duplicated genes. Our results indicate that segmental duplications are the source of the majority of full-length copy number polymorphic genes, most of the variant genes are organized as tandem duplications, and a significant fraction of these genes will represent paralogs with levels of sequence diversity beyond thresholds of allelic variation. In addition, these data provide a targeted set of CNV genes enriched for regions likely to be associated with human phenotypic differences due to copy number changes and present a source of copy number responsive oligonucleotide probes for future association studies.

Project description:BackgroundGenomic DNA copy number aberrations are frequent in solid tumors, although the underlying causes of chromosomal instability in tumors remain obscure. Genes likely to have genomic instability phenotypes when mutated (e.g. those involved in mitosis, replication, repair, and telomeres) are rarely mutated in chromosomally unstable sporadic tumors, even though such mutations are associated with some heritable cancer prone syndromes.MethodsWe applied array comparative genomic hybridization (CGH) to the analysis of breast tumors. The variation in the levels of genomic instability amongst tumors prompted us to investigate whether alterations in processes/genes involved in maintenance and/or manipulation of the genome were associated with particular types of genomic instability.ResultsWe discriminated three breast tumor subtypes based on genomic DNA copy number alterations. The subtypes varied with respect to level of genomic instability. We find that shorter telomeres and altered telomere related gene expression are associated with amplification, implicating telomere attrition as a promoter of this type of aberration in breast cancer. On the other hand, the numbers of chromosomal alterations, particularly low level changes, are associated with altered expression of genes in other functional classes (mitosis, cell cycle, DNA replication and repair). Further, although loss of function instability phenotypes have been demonstrated for many of the genes in model systems, we observed enhanced expression of most genes in tumors, indicating that over expression, rather than deficiency underlies instability.ConclusionMany of the genes associated with higher frequency of copy number aberrations are direct targets of E2F, supporting the hypothesis that deregulation of the Rb pathway is a major contributor to chromosomal instability in breast tumors. These observations are consistent with failure to find mutations in sporadic tumors in genes that have roles in maintenance or manipulation of the genome.

Dataset Information

Dynamics and processes of copy number instability in human gamma-globin genes.

Publications

Dynamics and processes of copy number instability in human gamma-globin genes.

Similar Datasets

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