Low variability of the POLG (CAG)n repeat in north Eurasian populations.

We investigated the frequency of different repeat-length alleles of the trinucleotide CAG microsatellite repeat in the coding sequence of the nuclear gene for the catalytic subunit of mitochondrial DNA polymerase gamma (POLG) in 12 ethnic groups from northern Eurasia. The population sample consisted of 1,330 individuals from 3 large geographic areas: Europe, Southwest Asia, and Siberia/East Asia. We found that the 10-repeat allele of the POLG gene is the most frequent in all analyzed populations, with a frequency of 88-96%. The heterozygosity level ranges from 22% in Europe to 13.6% in Southwest Asia with the lowest value of 7.4% in Siberia/East Asia. The present study provides evidence of clinal distribution of POLG gene heterozygosity in North Eurasian populations. In general, we found an extremely low variability of the trinucleotide CAG microsatellite repeat, suggesting that purifying selection acts against deleterious alleles, although low mutability of the repeated region cannot be ruled out.

Mitochondrial DNA variation in the aboriginal populations of the Altai-Baikal region: implications for the genetic history of North Asia and America.

The discovery of mtDNA types common to Asians and Amerinds (types A, B, C, and D) forced investigators to search for those nations of Asia which, though not considered the ancestors of the Amerinds, have retained a close genetic resemblance with them. We collected samples and studied the gene pools of the Turkic-speaking nations of South Siberia: Altaians, Khakassians, Shorians, Tuvinians, Todjins, Tofalars, Sojots, as well as Mongolian-speaking Buryats. The data indicate that nearly all Turkic-speaking nations of Siberia and Central Asia, as well as the Buryats, have types A, B, C, and D in their gene pool. The highest total frequency of these types is observed in the Tuvinians and Sojots. They, as well as the Buryats, also have the lowest frequency of the europeoid types. The most mixed Asian-Europeoid gene pool examined turned out to be that of the Shorians. An important finding was the presence of type X in the Altaians, which had not yet been detected in Asia. As shown by computer analysis, this DNA sequence is not a late European admixture. Rather, the Altai variant X is ancient and can be close to the ancestral form of the variants of contemporary Europeans and Amerinds. The presented results prove that of all nations in Asia, the Turkic-speaking nations living between Altai and Baikal along the Sayan mountains are genetically closest to the Amerinds.

Bacteria in ovarioles of females from maleless families of ladybird beetles Adalia bipunctata L. (Coleoptera: Coccinellidae) naturally infected with Rickettsia, Wolbachia, and Spiroplasma.

Ovarioles were found to be infected with Spiroplasma, Wolbachia, and Rickettsia in Adalia bipunctata females with maleless progeny in different natural populations. Ooplasm was infected with few Wolbachia bacteria. In ooplasm infected by Rickettsia, bacteria were present in small foci. Spiroplasmas were found encapsulated into ooplasm from the wider intercellular spaces between epithelial and oocyte cells. The cytoplasm of follicular epithelia infected with Rickettsia was heavily destroyed, but the nucleus was intact and free from bacteria. The essential feature of follicular epithelium cells from Spiroplasma and Wolbachia infected A. bipunctata females was inclusions of three types: crystalline, filaments, and concentric myelin-like lamellae. Observations of smears prepared from ovaries of A. bipunctata from natural populations revealed a low concentration of bacteria within a microscopy field (less 10 bacteria) in more than 90% of specimens, and only a few ovaries were heavily infected. Two different ways of bacterial invasion of the oocyte are suggested: Spiroplasma-like, through the intercellular spaces in the epithelium and Rickettsia-like, through the cytoplasm of follicular epithelium cells. Bacteria were not found in germarium zones and we suggest that each follicle is infected from haemolymph.

History of infection with different male-killing bacteria in the two-spot ladybird beetle Adalia bipunctata revealed through mitochondrial DNA sequence analysis.

The two-spot ladybird beetle Adalia bipunctata (Coleoptera: Coccinellidae) is host to four different intracellular maternally inherited bacteria that kill male hosts during embryogenesis: one each of the genus Rickettsia (alpha-Proteobacteria) and Spiroplasma (Mollicutes) and two distinct strains of Wolbachia (alpha-Proteobacteria). The history of infection with these male-killers was explored using host mitochondrial DNA, which is linked with the bacteria due to joint maternal inheritance. Two variable regions, 610 bp of cytochrome oxidase subunit I and 563 bp of NADH dehydrogenase subunit 5, were isolated from 52 A. bipunctata with known infection status and different geographic origin from across Eurasia. Two outgroup taxa were also considered. DNA sequence analysis revealed that the distribution of mitochondrial haplotypes is not associated with geography. Rather, it correlates with infection status, confirming linkage disequilibrium between mitochondria and bacteria. The data strongly suggest that the Rickettsia male-killer invaded the host earlier than the other taxa. Further, the male-killing Spiroplasma is indicated to have undergone a recent and extensive spread through host populations. In general, male-killing in A. bipunctata seems to represent a highly dynamic system, which should prove useful in future studies on the evolutionary dynamics of this peculiar type of symbiont-host association.