Global patterns in human mitochondrial DNA and Y-chromosome variation caused by spatial instability of the local cultural processes

Because of the widespread phenomenon of patrilocality, it is hypothesized that Y-chromosome variants tend to be more localized geographically than those of mitochondrial DNA (mtDNA). Empirical evidence confirmatory to this hypothesis was subsequently provided among certain patrilocal and matrilocal groups of Thailand, which conforms to the isolation by distance mode of gene diffusion. However, we expect intuitively that the patterns of genetic variability may not be consistent with the above hypothesis among populations with different social norms governing the institution of marriage, particularly among those that adhere to strict endogamy rules. We test the universality of this hypothesis by analyzing Y-chromosome and mtDNA data in three different sets of Indian populations that follow endogamy rules to varying degrees. Our analysis of the Indian patrilocal and the matrilocal groups is not confirmatory to the sex-specific variation observed among the tribes of Thailand. Our results indicate spatial instability of the impact of different cultural processes on the genetic variability, resulting in the lack of universality of the hypothesized pattern of greater Y-chromosome variation when compared to that of mtDNA among the patrilocal populations.     

Austro-Asiatic tribes of Northeast India provide hitherto missing genetic link between South and Southeast Asia

Northeast India, the only region which currently forms a land bridge between the Indian subcontinent and Southeast Asia, has been proposed as an important corridor for the initial peopling of East Asia. Given that the Austro-Asiatic linguistic family is considered to be the oldest and spoken by certain tribes in India, Northeast India and entire Southeast Asia, we expect that populations of this family from Northeast India should provide the signatures of genetic link between Indian and Southeast Asian populations. In order to test this hypothesis, we analyzed mtDNA and Y-Chromosome SNP and STR data of the eight groups of the Austro-Asiatic Khasi from Northeast India and the neighboring Garo and compared with that of other relevant Asian populations. The results suggest that the Austro-Asiatic Khasi tribes of Northeast India represent a genetic continuity between the populations of South and Southeast Asia, thereby advocating that northeast India could have been a major corridor for the movement of populations from India to East/Southeast Asia.     

Microsatellite diversity in Andhra Pradesh, India: genetic stratification versus social stratification

DNA samples of 948 individuals belonging to 27 populations from southern Andhra Pradesh were analyzed for nine AmpFlSTR Profiler Plus loci. The nature and extent of genomic diversity within and between these populations have been examined with reference to socioeconomic and geographic affiliations. The results suggest that the average heterozygosity is uniformly high in these populations (> 0.80) and that the patterns of allele distributions are similar across the populations. The value of the coefficient of gene differentiation and the AMOVA and structure analysis results suggest that these populations are highly homogeneous. The neighbor-joining tree constructed using either D(A) or F(ST) distances suggests no intelligible pattern of population clusters based on ethnohistoric or geographic affiliations. All these observations suggest either a common recent origin of these populations or extensive gene flow across the populations that erased the original genetic differences. Given strict endogamy, the latter explanation can hold only if there has been unauthorized or unrecognized gene flow transecting the social boundaries. Nevertheless, the regression plot of average heterozygosity versus distance from the centroid (Rii), based on Harpending and Ward's (1982) model, and the genetic distances computed between different hierarchical groups within Andhra Pradesh tend to support this conjecture. Overall, the results suggest lack of a significant degree of genetic stratification that is consistent with social stratification in Andhra Pradesh. Furthermore, the neighbor-joining tree based on comparative data from other Indian and continental populations brings out a single and compact cluster of all the Andhra populations that is clearly separated from the rest.     

Population substructure and patterns of quantitative variation among the Gollas of southern Andhra Pradesh, India.

Population substructure and biological differentiation was studied among the Golla, a pastoral caste living in the southern areas of Andhra Pradesh (AP) in India, using 11 anthropometric measurements and 20 quantitative dermatoglyphic variables. The data were collected from a sample of 334 adult males drawn from 30 villages distributed in the Chittoor district of AP, who belonged to 8 endogamous subunits of the same caste. Multiple discriminant analysis of the anthropometrics suggests a highly significant degree of discrimination that is consistent with the microgeographic variations of the groups. In contrast, in different sets of dermatoglyphs discrimination is low and generally inconsistent with both the geographic and ethnohistorical affiliations of the groups. These findings are reflected in the F(ST) value for anthropometry, which is more than double the value of dermatoglyphs. The patterns of gene flow as inferred through the regression of phenotypic variance on the distance of groups from the centroid is not generally consistent with the known backgrounds in the case of either dermatoglyphs or anthropometry. It is concluded that at the level of caste substructure representing the lowest level of population hierarchy, the quantitative variables examined here may not portray a complete picture of the historical process of subdivision. The results of this study are not in congruence with those based on another study of 13 short tandem repeat loci on the same set of populations (Reddy et al. 2001), which may provide better insights into the population structure and history of subdivision that are consistent with the known ethnohistorical backgrounds of the populations.     

Current progress in use of adipose derived stem cells in peripheral nerve regeneration

Unlike central nervous system neurons; those in the peripheral nervous system have the potential for full regeneration after injury. Following injury, recovery is controlled by schwann cells which replicate and modulate the subsequent immune response. The level of nerve recovery is strongly linked to the severity of the initial injury despite the significant advancements in imaging and surgical techniques. Multiple experimental model shave been used with varying successes to augment the natural regenerative processes which occur following nerve injury. Stem cell therapy in peripheral nerve injury may be an important future intervention to improve the best attainable clinical results. In particular adipose derived stem cells(ADSCs) are multipotent mesenchymal stem cells similar to bone marrow derived stem cells, which are thought to have neurotrophic properties and the ability to differentiate into multiple lineages. They are ubiquitous within adipose tissue; they can form many structures resembling the mature adult peripheral nervous system. Following early in vitro work; multiple small and large animal in vivo models have been used in conjunction with conduits, autografts and allografts to successfully bridge the peripheral nerve gap. Some of the ADSC related neuroprotective and regenerative properties have been elucidated however much work remains before a model can be used successfully in human peripheral nerve injury(PNI). This review aims to provide a detailed overview of progress made in the use of ADSC in PNI, with discussion on the role of a tissue engineered approach for PNI repair.     

Genetic diversity and relationships among the tribes of Meghalaya compared to other Indian and Continental populations

The autosomal AmpFLSTR markers validated and widely used for forensic applications are used in this study to examine the extent of diversity and genetic relationships among nine Meghalaya populations. Altogether, 932 chromosomes from 9 populations were analyzed using 9 tetrameric AmpFLSTR loci. The included populations were all seven subtribes of the Austro-Asiatic Mon-Khmer-speaking Khasi and the neighboring Tibeto-Burman Garo. The Lyngngam, which are linguistically closer to the Khasi but are culturally intermediate between the Khasi and the Garo, are also included in the study. Although most of the microsatellite loci are highly polymorphic in each of these populations, the allele distributions are fairly uniform across the Meghalaya populations, suggesting relative homogeneity among them. Concurrent with this, the coefficient of gene differentiation (G(ST)) is observed to be low (0.026+/-0.002). This is naturally reflected in the lack of clear differentiation and clustering pattern of the Meghalaya tribes based on either geographic proximity or the historical or current affiliations of these tribes. Analysis of molecular variance (AMOVA) suggests no significant population structure. The structure analysis further suggests that, barring War-Khasi and Pnar, no other population shows any semblance of genetic identity. Even the position of the linguistically distinct Garo is not portrayed as separate from the Khasi. However, when comparable data from other Indian, Southeast Asian, and other continental populations were analyzed, the Meghalaya populations formed a compact cluster clearly separated from other populations, suggesting genetic identity of the Meghalaya populations as a whole. These results are concurrent with the hypothesis of a common and recent origin of these Meghalaya populations, whose genetic differentiation is overwhelmed by the homogenizing effect of continuous gene flow.