Abstract. The polyomavirus JC (JCV) is a doublestranded DNA virus that is ubiquitous in human populations and is excreted in urine by a large percentage of individuals (20–70%). The strong genetic stability, combined with a mechanism of transmission mainly within the family, makes JCV a good marker of human migrations. In this study, the coevolution of JCV with its human host is investigated by using over a thousand nucleotide sequences deposited in the EMBL database; they correspond to the IG region, which is the genomic region with the highest rate of variation. The pattern of genetic diversity in JCV is evaluated by the principal coordinates analysis and the construction of synthetic maps. The first principal coordinate supports the existence of two distinct virus lineages, both arising from the ancestral African type. The first synthetic map suggests a twomigration model of the human dispersal out of Africa, thus implying a more complex picture than that known from human genes. The second principal coordinate points out the distinctiveness of strains coming from Asian/Amerind populations. The picture yielded by the second synthetic map appears to be more consistent with that known from human genes. In fact, it provides evidence of a deep split of the Asian lineage of JCV into two main branches: one diffusing in Japan and Americas, the other in Southeast Asia. The view that JCV, with its peculiar feature of a dual early emergence from Africa, can provide new information about the evolutionary history of our ancestors is discussed.
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