Identification of the chromosome 12 translocation breakpoint region of a pleomorphic salivary gland adenoma with t(1;12)(p22;q15) as the sole cytogenetic abnormality

Abstract

Cell line Ad-312/SV40, which was derived from a primary pleomorphic salivary gland adenoma with t(1;12)(p22;q15), was used in fluorescence in situ hybridization (FISH) analysis to characterize its translocation breakpoint region on chromosome 12. Results of previous studies have indicated that the chromosome 12 breakpoint in Ad-312/SV40 is located proximally to locus D12S8 and distally to the CHOP gene. We here describe two partially overlapping yeast artificial chromosome (YAC) clones, Y4854 (500 kbp) and Y9091 (460 kbp), which we isolated in the context of a chromosome walking project with D12S8 and CHOP as starting points. We present a composite long-range restriction map encompassing the inserts of these two YAC clones and show by FISH analysis that both YACs span the chromosome 12 breakpoint as present in Ad-312/SV40 cells. Subsequently, we have isolated cosmid clones corresponding to various sequence-tagged sites (STSs) mapping within the inserts of these YAC clones. These included cRM51, cRM69, cRM85, cRM90, cRM91, cRM110, and cRM111. In FISH studies, cosmid clones cRM85, cRM90, and cRM111 appeared to map distally to the chromosome 12 breakpoint, whereas cosmid clones cRM51, cRM69, cRM91, and cRM110 were found to map proximally to it. These results assign the chromosome 12 breakpoint in Ad-312/SV40 to a DNA region of less than 165 kbp. FISH evaluation of the chromosome 12 breakpoints in five other pleomorphic salivary gland adenoma cell lines indicated that these are located proximally to the one in Ad-312/SV40, at a distance of more than 0.9 Mbp from STS RM91. These results, while pinpointing a potentially critical region on chromosome 12, also provide evidence for the possible involvement of 12q13-q15 sequences located elsewhere.