Microsatellite instability in IVS3 of murine c-fesgene: Tumor-associated rearrangement and mammalian divergence

The murine lymphomacrophage hybrids ESb, EbF1, EbF2-c4, which express c -fesconstitutively, were found by Southern analysis to bear a c -fesdeletion of almost 100 bp. The deleted allele was transmitted to the metastatic hybrids by their nonexpressing, poorly metastatic T-lymphoma progenitor Eb, which also has a structurally normal c -fesallele. PCR amplification and sequencing of fescDNA spanning exons 3–5, where the deletion mapped, ruled out any involvement of coding sequences in the rearrangement. PCR amplification of the as yet unsequenced murine c -fesIVS3 and IVS4 showed they are about 50% longer than their human and feline homologs. Sequencing of IVS4 showed no difference between tumor and control DNA. Sequencing of part of the ~2600-bp IVS3 was guided by the restriction analysis of PCR products from control and hybrid DNAs. This showed that differences from the control appeared to be mainly located in the 900-bp HindIII-EcoRI fragment, localized in the middle of IVS3. As all three hybrids had the same restriction map, this fragment was sequenced in one of them (ESb). A run of >200 CA repeats was found in control DNA, and a reduction in the CAnmicrosatellite accounted for most of the c-fesdeletion in the ESb hybrid. Interestingly, the 50% reduction in the size of human and feline c -fesIVS3 as compared with the murine homolog is mostly due to contraction of the same microsatellite.