BMC Cancer 2005, 5:102 http://www.biomedcentral.com/1471-2407/5/102 Table 3: Summary of mtDNA mutations in experimental mouse brain tumor cell linesa Brain tumor cell line EPEN CT-2A VM-NM VM-M Metastatic Host genetic background Nucleotide position Gene DNA change - - - + B6 B6 VM VM 9829 9461 5182 5182 15584 2159 Arg tRNA ND3 OL OL D-loop 16srRNA InsAA T->C InsA DelA T->C A->G a Tumor cell lines mtDNA sequences were compared to host strain brain mtDNA populations b Homo, homoplasmy; hetero, heteroplasmy c NA, not applicable Stateb Homo Homo Homo Homo Homo Hetero Amino acid change NAc Ile->Ile FHiegtueroep1lasmy in the metastatic VM-M tumor cell line Heteroplasmy in the metastatic VM-M tumor cell line. Mito- chondrial 16srRNA revealed a heteroplasmic mutation at position 2159 of an A to G transition. The three VM brain mitochondrial populations (LM, HM, and FM) displayed the same chromotagraph profile. The same level of heteroplasmy was observed in duplicate independent samples for the VM- M cell line. Arrow indicates heteroplasmic nucleotide at posi- tion 2159 compared to control. change of an isoleucine to methionine in the ND5 gene (Table 2). This transversion was found in all three brain mitochondrial populations for both strains and existed in all brain tumor cell lines corresponding to the host strain. This was the only variation found between the B6 strain sequence and the republished B6 sequence [23]. The VM strain also had two additional nucleotide variations compared to the B6 strain. The first variation was found in the ND3 gene at position 9461. This caused a T->C transi- tion, but resulted in no amino acid change. A second var- iation existed in the poly-A tract of the Arg tRNA, where an adenine was inserted at position 9829 (Table 2). The data show that few mtDNA variations exist between the B6 and VM inbred mouse strains. mtDNA somatic mutations in mouse brain tumor cell lines compared to syngeneic host mtDNA sequence Analysis of the EPEN brain tumor cell line revealed two somatic mutations compared to the syngeneic B6 host strain. One mutation involved an insertion of two adenines in the Arg tRNA at position 9829 (Table 3). This is not expected to alter Arg tRNA function because the mutation occurred in a highly variable site in mouse strains [23]. A second mutation involved a T->C transition in the ND3 gene at position 9461, but did not change the amino acid. Analysis of the CT-2A brain tumor cell line revealed only a single mutation compared to the syn- geneic B6 host strain. This involved an insertion of an ade- nine in the OL at position 5182 (Table 3). This mutation is also not likely to have functional consequence [23]. As in the chemically induced EPEN and CT-2A brain tumor cell lines, only a few somatic mutations were found in the VM brain tumor cell lines (VM-NM and VM-M) compared to the syngeneic VM host (Table 3). Two somatic mutations were found in the nonmetastatic VM- NM cell line. The first mutation involved a deletion of an adenine in the OL at position 5182. This is the same loca- tion where the only variation was found in the CT-2A tumor and is consistent with hypervariability in this Page 4 of 8 (page number not for citation purposes)