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Alu recombination-mediated structural deletions in the chimpanzee genome.

ABSTRACT: With more than 1.2 million copies, Alu elements are one of the most important sources of structural variation in primate genomes. Here, we compare the chimpanzee and human genomes to determine the extent of Alu recombination-mediated deletion (ARMD) in the chimpanzee genome since the divergence of the chimpanzee and human lineages ( approximately 6 million y ago). Combining computational data analysis and experimental verification, we have identified 663 chimpanzee lineage-specific deletions (involving a total of approximately 771 kb of genomic sequence) attributable to this process. The ARMD events essentially counteract the genomic expansion caused by chimpanzee-specific Alu inserts. The RefSeq databases indicate that 13 exons in six genes, annotated as either demonstrably or putatively functional in the human genome, and 299 intronic regions have been deleted through ARMDs in the chimpanzee lineage. Therefore, our data suggest that this process may contribute to the genomic and phenotypic diversity between chimpanzees and humans. In addition, we found four independent ARMD events at orthologous loci in the gorilla or orangutan genomes. This suggests that human orthologs of loci at which ARMD events have already occurred in other nonhuman primate genomes may be "at-risk" motifs for future deletions, which may subsequently contribute to human lineage-specific genetic rearrangements and disorders.

SUBMITTER: Han K

PROVIDER: S-EPMC2041999 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Understanding structure and function of human genome requires knowledge of genomes of our closest living relatives, the primates. Nucleotide insertions and deletions (indels) play a significant role in differentiation that underlies phenotypic differences between humans and chimpanzees. In this study, we evaluated distribution, evolutionary history, and function of indels found by comparing syntenic regions of the human and chimpanzee genomes.Specifically, we identified 6,279 indels of 10 bp or greater in a ~33 Mb alignment between human and chimpanzee chromosome 22. After the exclusion of those in repetitive DNA, 1,429 or 23% of indels still remained. This group was characterized according to the local or genome-wide repetitive nature, size, location relative to genes, and other genomic features. We defined three major classes of these indels, using local structure analysis: (i) those indels found uniquely without additional copies of indel sequence in the surrounding (10 Kb) region, (ii) those with at least one exact copy found nearby, and (iii) those with similar but not identical copies found locally. Among these classes, we encountered a high number of exactly repeated indel sequences, most likely due to recent duplications. Many of these indels (683 of 1,429) were in proximity of known human genes. Coding sequences and splice sites contained significantly fewer of these indels than expected from random expectations, suggesting that selection is a factor in limiting their persistence. A subset of indels from coding regions was experimentally validated and their impacts were predicted based on direct sequencing in several human populations as well as chimpanzees, bonobos, gorillas, and two subspecies of orangutans.Our analysis demonstrates that while indels are distributed essentially randomly in intergenic and intronic genomic regions, they are significantly under-represented in coding sequences. There are substantial differences in representation of indel classes among genomic elements, most likely caused by differences in their evolutionary histories. Using local sequence context, we predicted origins and phylogenetic relationships of gene-impacting indels in primate species. These results suggest that genome plasticity is a major force behind speciation events separating the great ape lineages.

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Alu recombination-mediated structural deletions in the chimpanzee genome.

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