Common origin of the human synovial sarcoma associated SS18 and SS18L1 gene loci

The highly conserved synovial sarcoma associated protein SS18 is thought to act as a transcriptional co-activator through interactions with various proteins involved in ( epigenetic) gene regulation. The SS18 SNH domain appears to act as a major interface for these protein-protein interactions. Previously, we used this SNH domain to identify SS18 paralogs ( SS18L1 and SS18L2) and orthologs in various species. The functional significance of these SS18-like proteins is embodied by the observations that SS18L1 and SS18L2 can replace SS18 in its various protein-protein interactions, and that SS18L1 may act as a fusion partner of SSX in synovial sarcoma. In the current study, we performed a comprehensive comparison of SNH-containing loci in several distinct species. By doing so, we found that the vertebrate SS18 and SS18L1 genes map within co-linear DNA segments that may have evolved through a relatively recent genomic duplication event. An additional phylogenetic study indicated that the more divergent SS18L2 gene is most likely derived from an earlier gene duplication event, again in the vertebrate lineage.