Identification of a unique Alu-based polymorphism and its use in human population studies

The impact of transposable elements in genome evolution and genetic instability and their implications in various diseases

Approximately 45% of the human genome is comprised of transposable elements (TEs). Results from the Human Genome Project have emphasized the biological importance of TEs. Many studies have revealed that TEs are not simply "junk" DNA, but rather, they play various roles in processes, including genome evolution, gene expression regulation, genetic instability, and cancer disposition. The effects of TE insertion in the genome varies from negligible to disease conditions. For the past two decades, many studies have shown that TEs are the causative factors of various genetic disorders and cancer. TEs are a subject of interest worldwide, not only in terms of their clinical aspects but also in basic research, such as evolutionary tracking. Although active TEs contribute to genetic instability and disease states, non-long terminal repeat transposons are well studied, and their roles in these processes have been confirmed. In this review, we will give an overview of the importance of TEs in studying genome evolution and genetic instability, and we suggest that further in-depth studies on the mechanisms related to these phenomena will be useful for both evolutionary tracking and clinical diagnostics.

Polymorphic insertions in 5 Alu loci within the major histocompatibility complex class I region and their linkage disequilibria with HLA alleles in four distinct populations in mainland China

In this study, we investigated the five polymorphic Alu loci located within human major histocompatibility complex (MHC) class I region in 445 individuals from four distinct Chinese populations: Hunan Han, Inner Mongolia Han, Inner Mongolia Mongol and Guangdong Han populations, with an emphasis on the linkage disequilibrium (LD) between Alu insertions and human leukocyte antigen (HLA)-A, Cw and B loci in a southern (Hunan Province) and a northern (Inner Mongolia Autonomous Region) Chinese Han population. Our data showed that (a) the allele and haplotype frequencies of Alu and HLA-A loci did not differ significantly between the two southern Chinese Han populations and showed remarkable homogeneity in the two northern Chinese populations; (b) AluyHG had the highest insertion rate and HLA-A*02 harboring the single AluyHG insertion was most frequent among Alu insertion-bearing haplotypes in all four populations; (c) haplotypes AluyHF insertion-HLA-A*26, AluyHG insertion-HLA-A*02 and AluyHJ insertion-HLA-A*24 were in significant LD across the four groups and (d) haplotype AluyMICB insertion-HLA-Cw*06 was in significant LD in both populations, while significant LD of haplotypes AluyMICB insertion-HLA-B*54 and AluyMICB insertion-HLA-B*48 was only observed in the Hunan Han population and the Inner Mongolia Han population, respectively. Haplotype HLA-B*48-MICA gene deletion-AluyMICB insertion was observed at a frequency of about 3.85% in the latter population. Our data, together with previous reports on several Asian-Oceanian populations suggest the identity by descent of several common HLA-A allelic lineages in these modern human populations. The novel population-specific LD patterns uncovered in this study also shed new insight into HLA evolution and haplotype origin.