What regulates mitochondrial DNA copy number in animal cells?

The study of the control of mitochondrial DNA copy number spans several decades and has identified many factors involved in the replication of the mitochondrial genome. However, the mechanisms involved in the regulation of this process are still obscure, particularly in animal cells. During the past decade, however, the identification of human diseases associated with drastically reduced levels of mtDNA caused renewed interest in this topic. Here, I will discuss recent work that sheds some light on how animal cells might maintain and control mtDNA levels.