Cell type specificity in alternative splicing of the human mismatch repair gene hMSH2

Human non-polyposis colorectal cancer is caused by germline mutations in the DNA mismatch repair genes hMSH2 and hMHL1. Several alternatively spliced mRNA species of these genes are present in peripheral blood lymphocytes of normal individuals, which can confound RT-PCR based techniques of mutation detection. Using RT-PCR, we compared the pattern of alternative splicing in whole peripheral blood lymphocytes (PBLs), separated T and B cells, lymphoblastoid cell lines (LCLs) from the same individuals, and a variety of tissues. Alternatively spliced forms of hMLH1 lacking exons 9/10, 10/11 and 9/10/11 were found to have similar patterns of expression in T cells, B cells, and LCLs. By contrast, a subset of hMSH2 transcripts, some of which were produced by utilisation of novel splicing motifs, were generally expressed in T but not in B cells. LCLs derived from the same blood samples showed no expression of any hMSH2 splicing variants. The hMSH2 delta ex13 transcript, while absent from LCLs, was expressed in whole PBLs and both T and B cell fractions. This transcript was furthermore largely undetectable in tissues other than mononuclear blood cells. These data provide evidence for tissue specificity in the regulation of alternative splicing in hMSH2. In particular we show that LCLs generally do not express alternatively spliced forms of hMSH2 mRNA and are thus suited for RT-PCR based mutation screening in that gene.