Effects of allogenic mtDNA on the expression of tumor phenotypes. (A) Experimental (left) and spontaneous (right) lung metastasis phenotypes of the tumor cybrids. Metastatic phenotypes were examined by inoculation of the tumor cybrids containing allogenic mtDNA derived from different strain mice into the tail veins or under the skin of B6 mice. (B) Tumor formation phenotype of the tumor cybrids. Total numbers of 5 × 10⁶ tumor cybrids were inoculated under the skin of B6 mice (left). A mixture of P29mtB6 (2.5 × 10⁶) and P29mtNZB (2.5 × 10⁶) was also inoculated (left) to confirm the selective tumor formation of P29mtB6 (n = 6 for each group). Data are representative of two independent experiments (*, P < 0.005; **, P < 0.0005). Restriction enzyme (SphI) digestions of PCR products were performed to identify the mtDNA genotypes (right). After the digestion, NZB mtDNA produced 143- and 31-bp fragments, whereas B6 mtDNA remained 174-bp PCR products. Mixed cybrids represent a simple mixture of P29mtB6 and P29mtNZB. Tumors represent primary tumors formed by inoculation of the mixed cybrids. (A and B) Error bars represent SD. (C) Tumor formation phenotype of the tumor cybrids inoculated under the skin of the B6mtNZB mice. Data represent the mean ± SD (n = 6). Similar results were obtained in two independent experiments.