POLG and neoplasm: Other genes, like TFB2M and POLG, have been confirmed to have the same effect in regulating mtDNA copy number.24, 25 Consistent with these previous studies, we also found a significant increase in TFAM mRNA in apoptotic cells through gene chip analysis and qPCR, and we found that the mtDNA copy number of tumor cells decreased significantly after the downregulation of TFAM by shRNA-TFAM transfection.