THE SYCP1 LOCI OF THE MOUSE GENOME - SUCCESSIVE RETROPOSITIONS OF A MEIOTIC GENE DURING THE RECENT EVOLUTION OF THE GENUS

The murine Sycp1 gene is expressed at the early stages of meiosis. We show that it is composed of a number of small exons and localized on m ouse chromosome 3. In the laboratory strains, two retrogenes were also identified. The first one (Sycp1-ps1), on chromosome 7, has accumulat ed point mutations and deletions and is not transcribed. A second retr ogene (Sycp1-ps2), on chromosome 8, is inserted within the continuity of a moderately repeated element, in an intron of another gene (Cad11) . The two retroposition events can be dated to distinct periods in the evolution of the Muridae. Sycp1-ps2 has kept features indicative of a relatively recent origin, namely a nearly intact coding region, a pol y(A) tail, and 14-bp terminal repeats. Its recent origin was confirmed by the fact that it is found in all the laboratory strains of mice, b ut neither in a recent isolate from Mus musculus domesticus wild stock s nor in the closely related subspecies M. musculus musculus, M. m. mo lossinus, M. m. castaneus, and M. m. bactrianus. Appearance of the mor e ancient Sycp1-ps1 retrogene is concomitant with the radiation of the genus. It is present in various Mus species (M. spretus, M; spicilegu s, M. macedonicus, and M. cookii), but neither in the rat nor in the m ore closely related Pyromis genus. Transposition of retrotranscripts d uring meiosis and their hereditary establishment thus appear to occur relatively frequently. They may, therefore, play a significant role in the evolutionary process. (C) 1997 Academic Press.