Yuri E. Dubrova

Y-Chromosomal Diversity in Europe Is Clinal and Influenced Primarily by Geography, Rather than by Language

Clinal patterns of autosomal genetic diversity within Europe have been interpreted in previous studies in terms of a Neolithic demic diffusion model for the spread of agriculture; in contrast, studies using mtDNA have traced many founding lineages to the Paleolithic and have not shown strongly clinal variation. We have used 11 human Y-chromosomal biallelic polymorphisms, defining 10 haplogroups, to analyze a sample of 3,616 Y chromosomes belonging to 47 European and circum-European populations. Patterns of geographic differentiation are highly nonrandom, and, when they are assessed using spatial autocorrelation analysis, they show significant clines for five of six haplogroups analyzed. Clines for two haplogroups, representing 45% of the chromosomes, are continentwide and consistent with the demic diffusion hypothesis. Clines for three other haplogroups each have different foci and are more regionally restricted and are likely to reflect distinct population movements, including one from north of the Black Sea. Principal-components analysis suggests that populations are related primarily on the basis of geography, rather than on the basis of linguistic affinity. This is confirmed in Mantel tests, which show a strong and highly significant partial correlation between genetics and geography but a low, nonsignificant partial correlation between genetics and language. Genetic-barrier analysis also indicates the primacy of geography in the shaping of patterns of variation. These patterns retain a strong signal of expansion from the Near East but also suggest that the demographic history of Europe has been complex and influenced by other major population movements, as well as by linguistic and geographic heterogeneities and the effects of drift.

Critical evaluation of ECV304 as a human endothelial cell model defined by genetic analysis and functional responses: A comparison with the human bladder cancer derived epithelial cell line t24/83

Early reports indicated that ECV304 was a spontaneously-transformed line derived from a Japanese human umbilical vein endothelial cells (HUVEC) culture. Many morphological, immunochemical, and genetic studies provided further evidence that ECV304 was a valuable biomedical research tool and could be used to study processes that include angiogenesis in vitro and signal transduction by a variety of G protein-coupled receptors. However, several distinct differences between ECV304 and HUVEC are now apparent and recent reports have indicated genetic similarity between ECV304 and T24/83, a human bladder cancer cell line. To further assess the utility of ECV304 as a human endothelial cell model, we compared the functional responses of ECV304 and T24/83 to a range of G protein-coupled receptor agonists. We also used DNA fingerprinting to karyotype both ECV304 and T24/83. Both ATP and uridine triphosphate (UTP) stimulated inositol phosphate metabolism in ECV304 without alteration of cAMP levels. Comparative data using selective P2Y receptor agonists indicated that this response, leading to calcium mobilization from intracellular stores, was predominantly mediated by the activation of P2Y2 receptors. Similar responses were recorded from both ECV304 and T24/83 cells. ECV304 expressed a relatively high basal activity of NOS that was reduced by L-NAME and stimulated by P2Y2 receptor agonists. In contrast, P2Y2 receptor activation did not induce prostaglandin synthesis in ECV304. Both ECV304 and T24/83 express receptors for adenosine, adrenaline, and calcitonin, which stimulate adenylate cyclase. Proliferation of ECV304 and T24/83 cells, measured by the incorporation of [3H]thymidine into DNA, was largely serum-independent. This was in contrast to parallel experiments with porcine and bovine aortic endothelial cells that indicated a marked serum-dependent increase in DNA synthesis. Genetic analysis confirmed that ECV304 and T24/83 are identical. ECV304 displays some endothelial characteristics and is useful for the study of receptor pharmacology. However, ECV304 is not of HUVEC origin and is therefore an inappropriate cell line to study endothelial cell biology.

Radiation-induced transgenerational instability

To date, the analysis of mutation induction has provided an irrefutable evidence for an elevated germline mutation rate in the parents directly exposed to ionizing radiation and a number of chemical mutagens. However, the results of numerous publications suggest that radiation may also have an indirect effect on genome stability, which is transmitted through the germ line of irradiated parents to their offspring. This review describes the phenomenon of transgenerational instability and focuses on the data showing increased cancer incidence and elevated mutation rates in the germ line and somatic tissues of the offspring of irradiated parents. The possible mechanisms of transgenerational instability are also discussed.

Elevated minisatellite mutation rate in the post-chernobyl families from ukraine.

Germline mutation at eight human minisatellite loci has been studied among families from rural areas of the Kiev and Zhitomir regions of Ukraine, which were heavily contaminated by radionuclides after the Chernobyl accident. The control and exposed groups were composed of families containing children conceived before and after the Chernobyl accident, respectively. The groups were matched by ethnicity, maternal age, parental occupation, and smoking habits, and they differed only slightly by paternal age. A statistically significant 1.6-fold increase in mutation rate was found in the germline of exposed fathers, whereas the maternal germline mutation rate in the exposed families was not elevated. These data, together with the results of our previous analysis of the exposed families from Belarus, suggest that the elevated minisatellite mutation rate can be attributed to post-Chernobyl radioactive exposure. The mechanisms of mutation induction at human minisatellite loci are discussed.

Radiation-induced transgenerational alterations in genome stability and DNA damage

Mutation induction in directly exposed cells is currently regarded as the main component of the genetic risk of ionizing radiation for humans. However, recent data on the transgenerational increases in mutation rates in the offspring of irradiated parents indicate that the genetic risk could be greater than predicted previously. Here, we have analysed transgenerational changes in mutation rates and DNA damage in the germline and somatic tissues of non-exposed first-generation offspring of irradiated inbred male CBA/Ca and BALB/c mice. Mutation rates at an expanded simple tandem repeat DNA locus and a protein-coding gene (hprt) were significantly elevated in both the germline (sperm) and somatic tissues of all the offspring of irradiated males. The transgenerational changes in mutation rates were attributed to the presence of a persistent subset of endogenous DNA lesions (double- and single-strand breaks), measured by the phosphorylated form of histone H2AX (γ-H2AX) and alkaline Comet assays. Such remarkable transgenerational destabilization of the F1 genome may have important implications for cancer aetiology and genetic risk estimates. Our data also provide important clues on the still unknown mechanisms of radiation-induced genomic instability.

A novel single molecule analysis of spontaneous and radiation-induced mutation at a mouse tandem repeat locus

Expanded simple tandem repeat (ESTR) loci include some of the most unstable DNA in the mouse genome and have been extensively used in pedigree studies of germline mutation. We now show that repeat DNA instability at the mouse ESTR locus Ms6-hm can also be monitored by single molecule PCR analysis of genomic DNA. Unlike unstable human minisatellites which mutate almost exclusively in the germline by a meiotic recombination-based process, mouse Ms6-hm shows repeat instability both in germinal (sperm) DNA and in somatic (spleen, brain) DNA. There is no significant variation in mutation frequency between mice of the same inbred strain. However, significant variation occurs between tissues, with mice showing the highest mutation frequency in sperm. The size spectra of somatic and sperm mutants are indistinguishable and heavily biased towards gains and losses of only a few repeat units, suggesting repeat turnover by a mitotic replication slippage process operating both in the soma and in the germline. Analysis of male mice following acute pre-meiotic exposure to X-rays showed a significant increase in sperm but not somatic mutation frequency, though no change in the size spectrum of mutants. The level of radiation-induced mutation at Ms6-hm was indistinguishable from that established by conventional pedigree analysis following paternal irradiation. This confirms that mouse ESTR loci are very sensitive to ionizing radiation and establishes that induced germline mutation results from radiation-induced mutant alleles being present in sperm, rather than from unrepaired sperm DNA lesions that subsequently lead to the appearance of mutants in the early embryo. This single molecule monitoring system has the potential to substantially reduce the number of mice needed for germline mutation monitoring, and can be used to study not only germline mutation but also somatic mutation in vivo and in cell culture.

Wheat mutation rate after Chernobyl

The accident at the Chernobyl nuclear power plant in 1986 has generated concern over the genetic consequences of chronic exposure to radiation. Here we describe a new approach to monitoring germline mutation in plants and find evidence for a remarkably strong induction of germline mutation in wheat upon chronic exposure to ionizing radiation produced by the Chernobyl accident.

Germline mutation induction at mouse repeat DNA loci by chemical mutagens.

Mutation rates at two expanded simple tandem repeat (ESTR) loci were studied in the germline of male mice exposed to two monofunctional alkylating agents, ethylnitrosourea (ENU) and isopropyl methanesulfonate (iPMS), and a topoisomerase II inhibitor, etoposide. Pre-meiotic exposure to the alkylating agents resulted in a highly significant increase in ESTR mutation rate, but did not alter post-meiotically exposed cells. Pre-meiotic mutation induction by ENU and iPMS was linear within the interval of doses from 12.5 to 25mg/kg and reached a plateau at higher concentrations. Paternal exposure to etoposide resulted in ESTR mutation induction at meiotic stages but did not affect post- or pre-meiotic cells. The pattern of ESTR mutation induction after pre-meiotic and meiotic exposure to chemical mutagens was similar to that previously obtained by various traditional approaches for monitoring germline mutation in mice. The results of this study show that ESTR loci provide a new efficient experimental system for monitoring the genetic effects of chemical mutagens, capable of detecting increases in mutation rates at low doses of exposure.

Radiation-induced germline instability at minisatellite loci

PURPOSE To review the results of recent studies on radiation-induced germline instability at mammalian minisatellite loci. RESULTS Evidence has been obtained recently that germline mutation at minisatellites is remarkably sensitive to ionizing radiation, in both mice and humans. In mice, an elevated mutation rate was found after acute irradiation of pre-meiotic spermatogonia, with a doubling dose of 0.33 Gy, a value close to those obtained in mice after acute spermatogonia irradiation using other systems for mutation detection. In humans, analysis of germline mutation rate at minisatellites among children born in areas of the Mogilev district of Belarus, which was heavily polluted after the Chernobyl accident, has shown a twofold higher mutation rate in exposed families compared with non-irradiated families from the United Kingdom. Within the Belarus cohort, the mutation rate was significantly greater in families exposed to a higher parental radiation dose, consistent with radiation induction of germline mutation. The data in this study also demonstrate the indirect nature of radiation-induced germline mutation at mammalian minisatellite loci suggesting a strong similarity with the phenomenon of genomic instability in somatic cells. CONCLUSIONS Minisatellite loci provide a powerful system for the efficient monitoring of germline mutation in humans and are capable of detecting induced mutations in relatively small population samples.

Induction of minisatellite mutations in the mouse germline by low-dose chronic exposure to γ-radiation and fission neutrons.

Germline mutation induction at mouse minisatellite loci by paternal low-dose (0.125-1 Gy) exposure to chronic (1.66 x 10(-4) Gy min(-1)) low-linear energy transfer (low-LET) gamma-irradiation and high-LET fission neutrons (0.003 Gy min(-1)) was studied at pre-meiotic stages of spermatogenesis. Both types of radiation produced linear dose-response curves for mutation of the paternal allele. In contrast to previous results using higher doses, the pattern of induction of minisatellite mutation after chronic gamma-irradiation was similar to acute (0.5 Gy min(-1)) exposure to X-rays, indicating that the elevated mutation rate was independent of the ability of the cell to repair damage induced immediately or over a period of up to 100 h. Chronic exposure to fission neutrons was more effective than acute or chronic low-LET exposure (relative biological effectiveness, RBE=3.36). The data also provide strong support for the previous conclusion that increases in minisatellite mutation rate are not caused by radiation-induced DNA damage at minisatellite loci themselves, but rather from damage induced by ionising radiation elsewhere in the genome/cell.