C57BL/6J contains a mus spretus-like line-1 element within a spretus haplotype

The Mus musculus domesticus strain C57BL/6J contains several LINE-1 elements recently derived from Mus spretus, including L1C105. The evidence indicates that these two mouse species exchanged genetic information long after their known speciation date. Because LINE-1 is a transposable element with approximately 105 copies per mammalian genome, it is unclear if the spretuslike LINE-ls in C57BL/6J arrived at their present positions by transposition into domesticus DNA or if they remain in a segment of spretus DNA. This ques tion was answered by analyzing the sequence flanking L1C105 in comparison with those of a variety of other spretus and musculus mice. We found that L1C105 is located within a retroviral-related sequence (MuERVC-0105), that occupies the same locus in most of the M. m. domesticus and M. spretus strains surveyed indicating that it inserted before the speciation. Thus it did not move during the time period in question. Comparing the sequences of 1081bp of MuERVC-Cl05 from C57BL/6J and SPRET/Ei showed they are identical, indicating that it also recently came from spretus. Analysis of a unique sequence flanking MuERVC-C105 suggests that the unique sequence too is a spretus allele. However, the existence of ancestral polymorphisms in spretus at this locus makes finding the recombinational boundary difficult. This work was supported by NIH grants HG00190 and GM51847.