Polymorphic Alu Insertions Research Articles

Role of Alu Element in Detecting Population Diversity

Indel polymorphisms are becoming increasingly useful markers for population genetic studies. These are stable mutational events that are unlikely to undergo reverse or convergent mutations, making them useful as markers for distinguishing chromosomal lineages identical by descent and for using in population diversity studies. There has been a great deal of interest to use retrotransposones like Alu element, which displays indel polymorphism, in the population diversity studies. The polymorphic Alu insertions are particularly useful for such studies because the probability of independent retroposition at the same exact chromosomal site is virtually zero. All loci carrying a particular Alu insertion are derived from a unique event and hence are identical by descent. Further the ancestral state for polymorphic Alu insertions is the absence of the insertion hence the direction of mutational change is the gain of the Alu element at a particular locus. Knowing the ancestral state and the direction of mutational change greatly facilitates the analysis of population relationship but is generally not possible for other types of loci. These features make Alu insertion polymorphisms more attractive than other autosomal classical markers for analyses of population history and structure. This review is focused on Alu element and its role in detecting population diversity with few empirical examples from around the world. The phylogenetic studies based on Alu polymorphisms on Indian populations has also been presented.

New insights into the genetic history of Tunisians: Data from Alu insertion and apolipoprotein E gene polymorphisms

Background: Among polymorphisms of non-transcribed DNA sequences and functional genes, those of Alu insertions and that of the APOE gene have been widely used to clarify the degree of genetic relationships between human populations.Aim: APOE gene and eight Alu insertion polymorphisms were investigated in Tunisians and compared with data from neighbour populations in order to gain new insights into the genetic position of Tunisia in the Mediterranean region.Subjects and methods: A total of 121 individuals from the North and Centre-South regions were sampled.Results: No significant genetic differences were found between Tunisians and North Africans when samples representative of wide areas were considered. APOE gene variation seemed slightly less powerful than the Alu polymorphisms in detecting North–South Mediterranean differences.Conclusion: North African populations show a substantial degree of genetic homogeneity, which may reflect the similarity of their origins, mainly when samples from large geographical areas are compared. The relative genetic homogeneity of the whole Mediterranean region probably reflects a common origin and/or remarkable levels of gene flow. However, this gene flow has not yet erased the differentiation between the two Mediterranean shores, as revealed by Alu insertion polymorphisms.

ALU Insertion Polymorphisms in Populations of the South Caucasus

An analysis of eight Alu insertion loci (ACE, ApoA1, PV92, TPA25, NBC27, NBC102, NBC148 and NBC182) was carried out in three ethnic groups of the South Caucasus (Abkhazians, Armenians and Georgians). Genetic differentiation between these groups (Gst = 1%) was half as much as in European populations and four time less than in populations of Dagestan. Although it was not possible to determine a contribution of Neolithic farmers to the Caucasian gene pool, the principal component analysis showed clear differences between these populations and those of Europe, Siberia and Asia. No evidence of correlation between genetic and linguistic data in our populations was disclosed. However, long-term habitation on common territory has led to common cultural, anthropological and detectable genetic traits.

Effects of the Y Chromosome on Cardiovascular Risk Factors in Japanese Men

Excess cardiovascular risk in men compared with women has been suggested to be partly explained by effects of the Y chromosome. However, inconsistent results have been reported on the Y chromosome's genetic influence on blood pressure and lipid levels. The purpose of the present study was to settle the question whether genetic variants of the Y chromosome influence cardiovascular risk factors using a large epidemiological cohort, the Suita study. Possible influences of the Y chromosome polymorphisms (Y chromosome Alu insertion polymorphism [YAP], M175 and SRY+465) on cardiovascular risk factors were assessed in 974 Japanese men. The frequency of the YAP(+) allele in our study sample was 0.31. The prevalence of hypertension tended to be higher in YAP(+) than in YAP(-) men, and this tendency was found to be stronger among men aged 65 years or older. Men with the YAP(+) genotype had higher levels of high density lipoprotein (HDL) cholesterol compared with those with the YAP(-) genotype, even after adjustment for age, body mass index, and daily ethanol and cigarette consumption (57.0+/-14.6 mg/dL vs. 54.2+/-14.2 mg/dL, nominal p=0.011, adjusted p=0.0062). However, these observed nominal associations disappeared after adjusting for multiple testing (Bonferroni). No association was detected between the YAP genotype and myocardial infarction. Similarly, none of the associations with M175 and SRY+465 attained significance when multiple testing was taken into account. In conclusion, Y chromosome polymorphisms (YAP, M175 and SRY+465) do not appear to be associated with cardiovascular risk factors in Japanese men. Studies using much larger sample sizes and/or additional independent samples will be required for definitive conclusions.

Alu insertion polymorphisms and an assessment of the genetic contribution of Central Asia to Anatolia with respect to the Balkans

In the evolutionary history of modern humans, Anatolia acted as a bridge between the Caucasus, the Near East, and Europe. Because of its geographical location, Anatolia was subject to migrations from multiple different regions throughout time. The last, well-known migration was the movement of Turkic speaking, nomadic groups from Central Asia. They invaded Anatolia and then the language of the region was gradually replaced by the Turkic language. In the present study, insertion frequencies of 10 Alu loci (A25 = 0.07, APO = 0.96, TPA25 = 0.44, ACE = 0.37, B65 = 0.57, PV92 = 0.18, FXIIIB = 0.52, D1 = 0.40, HS4.32 = 0.66, and HS4.69 = 0.30) have been determined in the Anatolian population. Together with the data compiled from other databases, the similarity of the Anatolian population to that of the Balkans and Central Asia has been visualized by multidimensional scaling method. Analysis suggested that, genetically, Anatolia is more closely related with the Balkan populations than to the Central Asian populations. Central Asian contribution to Anatolia with respect to the Balkans was quantified with an admixture analysis. Furthermore, the association between the Central Asian contribution and the language replacement episode was examined by comparative analysis of the Central Asian contribution to Anatolia, Azerbaijan (another Turkic speaking country) and their neighbors. In the present study, the Central Asian contribution to Anatolia was estimated as 13%. This was the lowest value among the populations analyzed. This observation may be explained by Anatolia having the lowest migrant/resident ratio at the time of migrations.

A Worldwide Phylogeography for the Human X Chromosome

BackgroundWe reasoned that by identifying genetic markers on human X chromosome regions where recombination is rare or absent, we should be able to construct X chromosome genealogies analogous to those based on Y chromosome and mitochondrial DNA polymorphisms, with the advantage of providing information about both male and female components of the population.Methodology/Principal FindingsWe identified a 47 Kb interval containing an Alu insertion polymorphism (DXS225) and four microsatellites in complete linkage disequilibrium in a low recombination rate region of the long arm of the human X chromosome. This haplotype block was studied in 667 males from the HGDP-CEPH Human Genome Diversity Panel. The haplotypic diversity was highest in Africa (0.992±0.0025) and lowest in the Americas (0.839±0.0378), where no insertion alleles of DXS225 were observed. Africa shared few haplotypes with other geographical areas, while those exhibited significant sharing among themselves. Median joining networks revealed that the African haplotypes were numerous, occupied the periphery of the graph and had low frequency, whereas those from the other continents were few, central and had high frequency. Altogether, our data support a single origin of modern man in Africa and migration to occupy the other continents by serial founder effects. Coalescent analysis permitted estimation of the time of the most recent common ancestor as 182,000 years (56,700–479,000) and the estimated time of the DXS225 Alu insertion of 94,400 years (24,300–310,000). These dates are fully compatible with the current widely accepted scenario of the origin of modern mankind in Africa within the last 195,000 years and migration out-of-Africa circa 55,000–65,000 years ago.Conclusions/SignificanceA haplotypic block combining an Alu insertion polymorphism and four microsatellite markers on the human X chromosome is a useful marker to evaluate genetic diversity of human populations and provides a highly informative tool for evolutionary studies.

The distribution of major histocompatibility complex class I polymorphic Alu insertions and their associations with HLA alleles in a Chinese population from Malaysia

The frequency and association of polymorphic Alu insertions (POALINs) with human leucocyte antigen (HLA) class I genes within the class I genomic region of the major histocompatibility complex (MHC) have been reported previously for three populations: the Australian Caucasian, Japanese and north-eastern Thai populations. Here, we report on the individual insertion frequency of the five POALINs within the MHC class I region, their HLA-A and HLA-B associations, the POALIN haplotype frequencies and the HLA-A/POALIN four-loci haplotype frequencies in the Malaysian Chinese population. The phylogenetic relationship of the four populations based on the five POALIN allele frequencies was also examined. In the Malaysian Chinese population, the POALIN AluyHG was present at the highest frequency (0.560), followed by AluyHJ (0.300), AluyMICB (0.170), AluyTF (0.040) and AluyHF (0.030). The most frequent five-loci POALIN haplotype of the 16 inferred haplotypes was the AluyHG single insertion haplotype at a frequency of 0.489. Strong associations were present between AluyHJ and HLA-A24, HLA-A33 and HLA-A11 and between AluyHG and HLA-A2, HLA-A24 and HLA-A11, and these were reflected by the inferred haplotype frequencies constructed from the combination of the HLA-A locus and the AluyHG, AluyHJ and AluyHF loci. The strongest association of AluyMICB was with the HLA-B54 allele (five of five), whereas the associations with the other 17 HLA-B alleles were weak, moderate or undetermined. Phylogenetic analysis of the five POALIN allele frequencies places the Malaysian Chinese closest to the Japanese and north-eastern Thai populations in the same cluster and separate to the Australian Caucasian population. The MHC POALINs are confirmed in this study to be informative genetic markers in lineage (haplotype) analysis, population genetics and evolutionary relationships, especially in studying the MHC genomic region.

Polymorphic Alu insertions in five North‐West Italian populations

We analyzed the frequencies of eight human polymorphic Alu insertion loci in population samples from five towns in North-West Italy: Postua, Cavaglià, Biella, Torino, and Genova. All loci under scrutiny were found to be polymorphic in all samples, with the two exceptions of locus A25 in Postua, which was fixed for the absence of the Alu element, and APO in Genova, where the Alu insertion was fixed. Heterozigosity values were highly variable in all loci. F(ST) values for all loci indicate that most of the variability is found within populations, while between population variability is lower. In the multidimensional scaling (MDS) analysis plot, the studied populations are separated from the main group represented by European populations. The Postua sample is set apart also from neighboring towns as Cavaglià and Biella, confirming previous observations of the demographic isolation of this population.

In search of polymorphic Alu insertions with restricted geographic distributions

Alu elements are transposable elements that have reached over one million copies in the human genome. Some Alu elements inserted in the genome so recently that they are still polymorphic for insertion presence or absence in human populations. Recently, there has been an increasing interest in using Alu variation for studies of human population genetic structure and inference of individual geographic origin. Currently, this requires a high number of Alu loci. Here, we used a linker-mediated polymerase chain reaction method to preferentially identify low-frequency Alu elements in various human DNA samples with different geographic origins. The candidate Alu loci were subsequently genotyped in 18 worldwide human populations (∼370 individuals), resulting in the identification of two new Alu insertions restricted to populations of African ancestry. Our results suggest that it may ultimately become possible to correctly infer the geographic affiliation of unknown samples with high levels of confidence without having to genotype as many as 100 Alu loci. This is desirable if Alu insertion polymorphisms are to be used for human evolution studies or forensic applications.

Association of progesterone receptor gene polymorphism (PROGINS) with endometriosis, uterine fibroids and breast cancer

Endometriosis, uterine fibroids and breast cancer are female health disorders associated with a great deal of morbidity. Since all these disorders are hormone responsive, our present study has been carried out to identify the association of 306bp Alu insertion polymorphism in intron 7 of progesterone receptor gene (PROGINS). DNA was isolated from the blood samples of 445 Asian Indian women, which included 100 endometriosis, 80 fibroids and 157 cases of breast cancer along with 108 age matched normal healthy women as controls. PROGINS polymorphism was assessed by PCR followed by agarose gel electrophoresis. Results showed that T2 allele frequency is 5%, 10% and 14.6% in endometriosis, uterine fibroids and breast cancer, as compared to 5.5% in controls. This indicates that PROGINS can be considered as a predisposing risk marker for breast cancer but not for endometriosis and uterine fibroids.

Mechanism of Alu integration into the human genome

LINE-1 or L1 has driven the generation of at least 10% of the human genome by mobilising Alu sequences. Although there is no doubt that Alu insertion is initiated by L1-dependent target site-primed reverse transcription, the mechanism by which the newly synthesised 3' end of a given Alu cDNA attaches to the target genomic DNA is less well understood. Intrigued by observations made on 28 pathological simple Alu insertions, we have sought to ascertain whether microhomologies could have played a role in the integration of shorter Alu sequences into the human genome. A meta-analysis of the 1624 Alu insertion polymorphisms deposited in the Database of Retrotransposon Insertion Polymorphisms in Humans (dbRIP), when considered together with a re-evaluation of the mechanism underlying how the three previously annotated large deletion-associated short pathological Alu inserts were generated, enabled us to present a unifying model for Alu insertion into the human genome. Since Alu elements are comparatively short, L1 RT is usually able to complete nascent Alu cDNA strand synthesis leading to the generation of full-length Alu inserts. However, the synthesis of the nascent Alu cDNA strand may be terminated prematurely if its 3' end anneals to the 3' terminal of the top strand's 5' overhang by means of microhomology-mediated mispairing, an event which would often lead to the formation of significantly truncated Alu inserts. Furthermore, the nascent Alu cDNA strand may be 'hijacked' to patch existing double strand breaks located in the top-strand's upstream regions, leading to the generation of large genomic deletions.

Polymorphic Alu insertions and the genetic structure of Iberian Basques

Eight Alu sequences (ACE, TPA25, PV92, APO, FXIIIB, D1, A25 and B65) were analyzed in two samples from Navarre and Guipúzcoa provinces (Basque Country, Spain). Alu data for other European, Caucasus and North African populations were compiled from the literature for comparison purposes to assess the genetic relationships of the Basques in a broader geographic context. Results of both MDS plot and AMOVA revealed spatial heterogeneity among these three population clusters clearly defined by geography. On the contrary, no substantial genetic heterogeneity was found between the Basque samples, or between Basques and other Europeans (excluding Caucasus populations). Moreover, the genetic information obtained from Alu data conflicts with hypotheses linking the origin of Basques with populations from North Africa (Berbers) or from the Caucasus region (Georgia). In order to explain the reduced genetic heterogeneity detected by Alu insertions among Basque subpopulations, values of the Wright's F(ST )statistic were estimated for both Alu markers and a set of short tandem repeats (STRs) in terms of two geographical scales: (1) the Basque Country, (2) Europe (including Basques). In the Basque area, estimates of Wahlund's effect for both genetic markers showed no statistical difference between Basque subpopulations. However, when this analysis was performed on a European scale, F(ST) values were significantly higher for Alu insertions than for STR alleles. From these results, we suggest that the spatial heterogeneity of the Basque gene pool identified in previous polymorphism studies is relatively recent and probably caused by a differential process of genetic admixture with non-Basque neighboring populations modulated by the effect of a linguistic barrier to random mating.

Ancestral Alleles and Population Origins: Inferences Depend on Mutation Rate

Previous studies have found that at most human loci, ancestral alleles are "African," in the sense that they reach their highest frequency there. Conventional wisdom holds that this reflects a recent African origin of modern humans. This paper challenges that view by showing that the empirical pattern (of elevated allele frequencies within Africa) is not as pervasive as has been thought. We confirm this African bias in a set of mainly protein-coding loci, but find a smaller bias in Alu insertion polymorphisms, and an even smaller bias in noncoding loci. Thus, the strong bias that was originally observed must reflect some factor that varies among data sets--something other than population history. This factor may be the per-locus mutation rate: the African bias is most pronounced in loci where this rate is high. The distribution of ancestral alleles among populations has been studied using 2 methods. One of these involves comparing the fractions of loci that reach maximal frequency in each population. The other compares the average frequencies of ancestral alleles. The first of these methods reflects history in a manner that depends on the mutation rate. When that rate is high, ancestral alleles at most loci reach their highest frequency in the ancestral population. When that rate is low, the reverse is true. The other method--comparing averages--is unresponsive. Average ancestral allele frequencies are affected neither by mutation rate nor by the history of population size and migration. In the absence of selection and ascertainment bias, they should be the same everywhere. This is true of one data set, but not of 2 others. This also suggests the action of some factor, such as selection or ascertainment bias, that varies among data sets.

Pre- and Post-Columbian Gene and Cultural Continuity: The Case of the Gaucho from Southern Brazil

Objective: To investigate the evolutionary and demographic history of the Gaucho, a distinct population of southern Brazil, relating it to their culture, to assess possible parallel continuity. Methods: Six binary polymorphisms, an Alu insertion polymorphism (YAP) and 12 short tandem repeat loci in the non-recombining region of the Y-chromosome, as well as the sequence of the first hypervariable segment (HVS-I) of the mitochondrial DNA (mtDNA) control region were studied in 150 unrelated males born in the Pampa region of Rio Grande do Sul. Results: Comparison of the results with the other Brazilian and Uruguayan populations, as well as with their putative ancestors, indicated a stronger male Spanish influence than that observed elsewhere in Brazil, a former Portuguese colony. Extensive mtDNA analyses of their Amerindian component gave clear indications of the presence there of material from extinct (Charrua), as well as extant (Guarani) tribes. Conclusions: The genetic analyses contributed in a significant way to reveal that the known cultural continuity between pre- and post-Columbian Pampa populations was also accompanied by an extraordinary genetic continuity.

Mobile DNA elements in primate and human evolution

Roughly 50% of the primate genome consists of mobile, repetitive DNA sequences such as Alu and LINE1 elements. The causes and evolutionary consequences of mobile element insertion, which have received considerable attention during the past decade, are reviewed in this article. Because of their unique mutational mechanisms, these elements are highly useful for answering phylogenetic questions. We demonstrate how they have been used to help resolve a number of questions in primate phylogeny, including the human-chimpanzee-gorilla trichotomy and New World primate phylogeny. Alu and LINE1 element insertion polymorphisms have also been analyzed in human populations to test hypotheses about human evolution and population affinities and to address forensic issues. Finally, these elements have had impacts on the genome itself. We review how they have influenced fundamental ongoing processes like nonhomologous recombination, genomic deletion, and X chromosome inactivation.

Polymorphic Alu insertions among Mayan populations

The Mayan homeland within Mesoamerica spans five countries: Belize, El Salvador, Guatemala, Honduras and Mexico. There are indications that the people we call the Maya migrated from the north to the highlands of Guatemala as early as 4000 B.C. Their existence was village-based and agricultural. The culture of these Preclassic Mayans owes much to the earlier Olmec civilization, which flourished in the southern portion of North America. In this study, four different Mayan groups were examined to assess their genetic variability. Ten polymorphic Alu insertion (PAI) loci were employed to ascertain the genetic affinities among these Mayan groups. North American, African, European and Asian populations were also examined as reference populations. Our results suggest that the Mayan groups examined in this study are not genetically homogeneous.

The association between non‐melanoma skin cancer and a young dimorphic Alu element within the major histocompatibility complex class I genomic region

A non-melanoma skin cancer (NMSC) susceptibility locus within the major histocompatibility complex (MHC) class I region was previously identified telomeric of the HLA-C gene using high-density microsatellite markers. Here, we have extended the previous microsatellite study by using the same DNA samples obtained from 154 NMSC patients and 213 normal controls from the town of Busselton in Western Australia and examined the relationship between five polymorphic Alu insertions (POALINs) within the MHC class I region and their association with NMSC. The genotype distribution of the AluyTF insertion that is located within the NMSC susceptibility region telomeric of the HLA-C gene was significantly increased according to the Fisher's exact test in the NMSC patients, and it was not in Hardy-Weinberg equilibrium in the control group. There was no difference between the cancer patients and controls for the genotypes of the AluyMICB locus within intron 1 of the MICB gene and the other three POALINs (AluyHJ, AluyHG and AluyHF) that are located within the genomic region of the HLA-A, -G and -F gene cluster. The test for significant linkage disequilibrium for 10 pairs of POALIN loci and estimations of two locus POALIN haplotype frequencies also revealed AluyTF differences between the cases and controls. In conclusion, the MHC class I POALIN, AluyTF, that is located within the NMSC susceptibility locus and near the HLA-C gene was strongly associated with NMSC. This finding, using five different polymorphic Alu insertion markers, supports the previous microsatellite association study that one or more genes located in close proximity to the AluyTF insertion has a potential role in NMSC.

Genetic Change in the Polynesian Population of Easter Island: Evidence from Alu Insertion Polymorphisms

The origin of Pacific islanders is still an open issue in human population genetics. To address this topic we analyzed a set of 18 Alu insertion polymorphisms in a total of 176 chromosomes from native Easter Island inhabitants (Rapanui). Available genealogical records allowed us to subdivide the total island sample into two groups, representative of the native population living in the island around 1900, and another formed by individuals with some ancestors of non-Rapanui origin. Significant genetic differentiation was found between these groups, allowing us to make some biodemographic and historical inferences about the origin and evolution of this geographically isolated island population. Our data are consistent with equivalent and recent contributions from Amerindian and European migrants to the 1900s Rapanui population, with an accelerated increase in the European gene flow during the 20(th) century, especially since the 1960s. Comparative analysis of our results with other available Alu variation data on neighbouring populations supports the "Voyaging Corridor" model of Polynesian human settlement, which indicates that pre-Polynesians are mainly derived from Southeast Asian and Wallacean populations rather than from Taiwan or the Philippines. This study underlines the importance of sampling and taking into account historical information in genetic studies to unravel the recent evolution of human populations.

Proportioning Whole-Genome Single-Nucleotide–Polymorphism Diversity for the Identification of Geographic Population Structure and Genetic Ancestry

The identification of geographic population structure and genetic ancestry on the basis of a minimal set of genetic markers is desirable for a wide range of applications in medical and forensic sciences. However, the absence of sharp discontinuities in the neutral genetic diversity among human populations implies that, in practice, a large number of neutral markers will be required to identify the genetic ancestry of one individual. We showed that it is possible to reduce the amount of markers required for detecting continental population structure to only 10 single-nucleotide polymorphisms (SNPs), by applying a newly developed ascertainment algorithm to Affymetrix GeneChip Mapping 10K SNP array data that we obtained from samples of globally dispersed human individuals (the Y Chromosome Consortium panel). Furthermore, this set of SNPs was able to recover the genetic ancestry of individuals from all four continents represented in the original data set when applied to an independent, much larger, worldwide population data set (Centre d'Etude du Polymorphisme Humain-Human Genome Diversity Project Cell Line Panel). Finally, we provide evidence that the unusual patterns of genetic variation we observed at the respective genomic regions surrounding the five most informative SNPs is in agreement with local positive selection being the explanation for the striking SNP allele-frequency differences we found between continental groups of human populations.

Whole genome computational comparative genomics: A fruitful approach for ascertaining Alu insertion polymorphisms

Alu elements are the most active and predominant type of short interspersed elements (SINEs) in the human genome. Recently inserted polymorphic (for presence/absence) Alu elements contribute to genome diversity among different human populations, and they are useful genetic markers for population genetic studies. The objective of this study is to identify polymorphic Alu insertions through an in silico comparative genomics approach and to analyze their distribution pattern throughout the human genome. By computationally comparing the public and Celera sequence assemblies of the human genome, we identified a total of 800 polymorphic Alu elements. We used polymerase chain reaction-based assays to screen a randomly selected set of 16 of these 800 Alu insertion polymorphisms using a human diversity panel to demonstrate the efficiency of our approach. Based on sequence analysis of the 800 Alu polymorphisms, we report three new Alu subfamilies, Ya3, Ya4b, and Yb11, with Yb11 being the smallest known Alu subfamily. Analysis of retrotransposition activity revealed Yb11, Ya8, Ya5, Yb9, and Yb8 as the most active Alu subfamilies and the maintenance of a very low level of retrotransposition activity or recent gene conversion events involving S subfamilies. The 800 polymorphic Alu insertions are characterized by the presence of target site duplications (TSDs) and longer than average polyA-tail length. Their pre-integration sites largely follow an extended “NT-AARA” motif. Among chromosomes, the density of Alu insertion polymorphisms is positively correlated with the Alu-site availability and is inversely correlated with the densities of older Alu elements and genes.