Impaired intercellular adhesion and immature adherens junctions in merlin-deficient human primary schwannoma cells.

Schwannomas that occur spontaneously or in patients with neurofibromatosis Type 2, lack both alleles for the tumor suppressor and plasma membrane-cytoskeleton linker merlin. We have shown that human primary schwannoma cells display activation of the RhoGTPases Rac1 and Cdc42 which results in highly dynamic and ongoing protrusive activity like ruffling. Ruffling is an initial and temporally limited step in the formation of intercellular contacts like adherens junctions that are based on the cadherin-catenin system. We tested if there is a connection between Rac1-induced ongoing ruffling and the maintenance, stabilization and functionality of adherens junctions and if this is of relevance in human, merlin-deficient schwannoma cells. We show intense ongoing ruffling is not limited to membranes of single human primary schwannoma cells, but occurs also in membranes of contacting cells, even when confluent. Live cell imaging shows that newly formed contacts are released after a short time, suggesting disturbed formation or stabilization of adherens junctions. Morphology, high phospho-tyrosine levels and cortactin staining indicate that adherens junctions are immature in human primary schwannoma cells, whereas they display characteristics of mature adherens junctions in human primary Schwann cells. When merlin is reintroduced, human primary schwannoma cells show only initial ruffling in contacting cells and adherens junctions appear more mature. We therefore propose that ongoing Rac-induced ruffling causes immature adherens junctions and leads to impaired, nonfunctional intercellular adhesion in aggregation assays in merlin-deficient schwannoma cells that could be an explanation for increased proliferation rates due to loss of contact inhibition or tumor development in general.

Paternal and maternal lineages in the Balkans show a homogeneous landscape over linguistic barriers, except for the isolated Aromuns.

The Balkan Peninsula is a complex cultural mosaic comprising populations speaking languages from several branches of the Indo-European family and Altaic, as well as culturally-defined minorities such as the Aromuns who speak a Romance language. The current cultural and linguistic landscape is a palimpsest in which different peoples have contributed their cultures in a historical succession. We have sought to find any evidence of genetic stratification related to those cultural layers by typing both mtDNA and Y chromosomes, in Albanians, Romanians, Macedonians, Greeks, and five Aromun populations. We have paid special attention to the Aromuns, and sought to test genetically various hypotheses on their origins. MtDNA and Y-chromosome haplogroup frequencies in the Balkans were found to be similar to those elsewhere in Europe. MtDNA sequences and Y-chromosome STR haplotypes revealed decreased variation in some Aromun populations. Variation within Aromun populations was the primary source of genetic differentiation. Y-chromosome haplotypes tended to be shared across Aromuns, but not across non-Aromun populations. These results point to a possible common origin of the Aromuns, with drift acting to differentiate the separate Aromun communities. The homogeneity of Balkan populations prevented testing for the origin of the Aromuns, although a significant Roman contribution can be ruled out.

Alu insertion polymorphisms in the Balkans and the origins of the Aromuns.

We have analysed 11 human-specific Alu insertion polymorphisms in the Balkans to elucidate the origins of the Aromuns, a linguistic isolate inhabiting scattered areas in the Balkan Peninsula. Four Aromun samples (two from the Republic of Macedonia, one from Albania, and one from Romania) and five neighbouring populations (Macedonians, Albanians, Romanians, Greeks, and Turks) were analysed by means of genetic distances, principal components and analyses of the molecular variance (AMOVA). Three hypotheses were tested: Aromuns are Romanophonic Greeks; the result of a Romanian southward migration; or local descendants of the Thracians. The analyses show that the Aromuns do not constitute a homogeneous group separated from the rest of the Balkan populations. Grouping by language or geography does not explain the genetic differences observed in the region, suggesting a lack of genetic structure in the area. Aromuns do not seem to be particularly related to Greeks, Romanians, or to other Romance speakers. The Aromuns might have their origin to the south of the Danube river, with extensive gene flow with the neighbouring populations. The present results suggest a common ancestry of all Balkan populations, including Aromuns, with a lack of correlation between genetic differentiation and language or ethnicity, stressing that no major migration barriers have existed in the making of the complex Balkan human puzzle.