to the other populations, to hyper-methylation of the last three. Thus, in all 4 populations, residues or more specifically, residues that correspond to the sixth CTCF binding site displayed the same trend in response to SYT-SSX1 expression. In this regard therefore, population 3, the only population in which SYT/SSX1 did not induce IGF2 was also the only one in which the fusion did not induce an increase in methylation at the insulator binding site. Nevertheless, SYT-SSX1 significantly affected methylation of CpGs 23�C26 in this population but in the opposite direction to that observed in the other populations. We also assessed, by bisulfite transformation analysis, the methylation changes induced by SYT-SSX1 in a second region located outside the H19 ICR. This region, amplified by primers BS-13212sense and BS-13548antisense, was included in a CpG island located 39 to the H19 gene. Fifteen CpG sites were analyzed within this region. Allelic discrimination was possible in batches 1 and 4, which had a C/A polymorphism at position 13359 and a C/G polymorphism at position 13270. Allele-specific differential methylation was also observed in this region although not as markedly as in the ICR. The effect of SYT-SSX1 introduction varied from batch to batch. Strong hypomethylation was induced in batch 3 whereas batch 1 and 4 order TMC435 showed significant hypermethylation. This increase in methylation involved both alleles in batch 1 but was limited to only one allele in batch 4. We have analyzed the transcriptional effects of SYT-SSX1 expression in bone marrow derived human mesenchymal stem cells isolated from pediatric or adolescent patients. These cells may provide an appropriate model to study synovial sarcoma development, based on the generally recognized notion that SS originates from as yet unidentified pluripotent stem cells capable of mesenchymal and neuroectodermal differentiation. The only available transgenic model of SS thus far, 478-01-3 suggests that development of SS is linked to the expression of the early myogenic marker Myf5. Co-expression of early markers for different tissue lineages has been observed in MSCs, without necessarily being associated with loss of plasticit
