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Synovial sarcomas are highly malignant tumors of soft tissue which are characterized by the t(X;18) resulting in SYT-SSX fusion transcript production. Diagnosis of these tumors based on histology can be challenging, particularly when minimal biopsy specimens are presented to the pathologist. Demonstration by molecular methods of SYT-SSX transcripts is a useful adjunct for diagnosis in these situations. We have developed an assay, which combines one-step RT-multiplex PCR with capillary electrophoresis to detect and genotype the SYT-SSX transcripts from synovial sarcomas. Small amplicons from chimeric transcripts as well as GAPD transcripts are differentially labeled with fluorophores, allowing detection and size discrimination by capillary electrophoresis. In a study of 32 formalin-fixed soft tissue tumor specimens, the assay detected chimeric transcripts from 17/22 (77%) synovial sarcomas. All five assay negative specimens yielded no intact RNA as evidenced by lack of a GAPD amplicon. Chimeric transcripts were not detected in 9/9 malignant peripheral nerve sheath tumors or 1/1 epithelioid sarcoma. Representative amplicons were sequenced and confirmed the genotype results obtained by capillary electrophoresis. One-step RT-multiplex PCR combined with capillary electrophoresis is a rapid and accurate method for the detection and genotypic classification of SYT-SSX transcripts from fixed tissue specimens.

Nonhuman primates represent phylogenetic intermediates for studying the divergence of human and murine β 2 Ms. We report the nucleotide sequences of B 2 m cDNA clones from a baboon cell line, 26CB-1 ( Papio hamadryas ); primates: Cercopithecoida), and a cotton-top tamarin cell line, 1605L ( Saguinus oedipus ; primates: Ceboidea). The baboon and tamarin B 2 m sequences indicate a very slow rate of B 2 m evolution in primates relative to that in murid rodents. Phenotypic evolution of β 2 M has also been very conservative in primates, with only 9–14 substitutions separating baboon or tamarin β 2 Ms from those of humans or orangutans. Analyses of silent and amino-acid-altering nucleotide substitutions provide evidence that negative selection has acted to limit variability in β strands of primate β 2 Ms, while positive selection has promoted diversity in non-β-strand regions of murine β 2 Ms. No evidence for the action of selection upon β 2 M residues that contact the class I heavy chain was found in primates or mice. The finding that different selective forces have operated upon primate and murine β 2 Ms suggests that β 2 M may have evolved to serve distinct functions in primates and mice.