Multiple ways to prevent transmission of paternal mitochondrial DNA for maternal inheritance in animals

Mitochondria contain their own DNA (mtDNA). In most sexually reproducing organisms, mtDNA is inherited maternally (uniparentally); this type of inheritance is thus referred to as 'maternal (uniparental) inheritance'. Recent studies have revealed various mechanisms to prevent the transmission of sperm-derived paternal mtDNA to the offspring, thereby ensuring maternal inheritance of mtDNA. In the nematode Caenorhabditis elegans, paternal mitochondria and their mtDNA degenerate almost immediately after fertilization and are selectively degraded by autophagy, which is referred to as 'allophagy' (allogeneic [non-self] organelle autophagy). In the fruit fly Drosophila melanogaster, paternal mtDNA is largely eliminated by an endonuclease G-mediated mechanism. Paternal mitochondria are subsequently removed by endocytic and autophagic pathways after fertilization. In many mammals, including humans, paternal mitochondria enter fertilized eggs. However, the fate of paternal mitochondria and their mtDNA in mammals is still a matter of debate. In this review, we will summarize recent knowledge on the molecular mechanisms underlying the prevention of paternal mtDNA transmission, which ensures maternal mtDNA inheritance in animals.