Evolution of a complex minisatellite DNA sequence.

Minisatellites are tandem repeats of short DNA units widely distributed in genomes. However, the information on their dynamics in a phylogenetic context is very limited. Here we have studied the organization of the MsH43 locus in several species of primates and from these data we have reconstructed the evolutionary history of this complex minisatellite. Overall, with the exception of gibbon, MsH43 has an organization that is asymmetric, since the distribution of repeats is distinct between the 5' and 3' halves, and heterogeneous since there are many different repeats, some of them characteristic of each species. Inspection of the MsH43 arrays showed the existence of many duplications and deletions, suggesting the implication of slippage processes in the generation of polymorphism. Concerning the evolutionary history of this minisatellite, we propose that the birth of MsH43 may be situated before the divergence of Old World Monkeys since we found the existence of some MsH43 repeat motifs in prosimians and New World Monkeys. The analysis of MsH43 in apes revealed the existence of an evolutionary breakpoint in the pathway that originated African great apes and humans. Remarkably, human MsH43 is more homologous to orang-utan than to the corresponding sequence in gorilla and chimpanzee. This finding does not comply with the evolutionary paradigm that continuous alterations occur during the course of genome evolution. To adjust our results to the standard phylogeny of primates, we propose the existence of a wandering allele that was maintained almost unaltered during the period that extends between orang-utan and humans.