Figure 3.

The strict regulation of mtDNA copy number during development During oogenesis, mtDNA copy number exponentially increases to reach a peak at fertilization. Failure of the maturing oocyte to increase mtDNA copy number above the threshold (dotted blue line) can result in fertilization failure or early embryo arrest. mtDNA copy number per cell progressively decreases during preimplantation development until the blastocyst stage when replication is initiated in the trophectoderm only. The inner cell mass cells continue to reduce mtDNA copy number and the “mtDNA set point” is established, which is essential for mature cells to acquire the required numbers of mtDNA copy as their precursor cells undergo differentiation into their mature, fully functional forms. mtDNA, mitochondrial DNA.