ORIGIN AND EVOLUTION OF A MAJOR SATELLITE DNA FROM SOUTH-AMERICAN RODENTS OF THE GENUS CTENOMYS

This article is about the origin, amplification and evolution of the m ajor satellite DNA of South American rodents known popularly as tuco-t ucos (genus Ctenomys). This satellite DNA, named RPCS, differentially amplified during the evolution of Ctenomys species, which resulted in quantitative and qualitative differences in restriction-periodicity pa tterns among species. A rolling circle amplification model has been pr oposed to explain the qualitative and quantitative differences of RPCS sequences. RPCS-related sequences were also found in octodontines, bu t not in echimyids; that is, they arose in the common ancestor of cten omyines and octodontines. In situ hybridization experiments showed tha t RPCS is located in heterochromatic areas of the chromosomes. Finally , RPCS shows unusual features among satellite DNAs: it has a conspicuo us retroviral origin; The RPCS monomer has identity with the U3 region of a retroviral LTR, including promoters and enhancers. In addition, DNaseI protection assays showed that this sequences specifically bind transcription factors present in the nucleus of Ctenomys cells. The pu tative function that a retroviral sequence as RPCS may have played in shaping Ctenomys genome during evolution is discussed.