DNA-polymerase guided elimination of paternal mitochondrial genomes: An escape-proof obstacle to their transmission

Mitochondrial DNA is predominantly inherited from only one parent. In animals this is usually the mother. This program is not in the interest of the paternal mitochondrial genome whose potential to contribute to future generations is restricted. However, in a dramatic example of genetic conflict, nuclear programs ensure the outcome. Two large mitochondria extend the length of Drosophila sperm tails. The hundreds of nucleoids in these mitochondria vanish during spermatogenesis eliminating their potential for transmission. Our previous work showed that mutational inactivation of EndoG, a nuclear encoded mitochondrial endonuclease, slows elimination of mitochondrial genomes. Here, we show that knockdown of the nuclearly encoded mitochondrial DNA polymerase, Tamas, produces a much more complete block of mtDNA loss. Recruitment of Tamas to the nucleoid at the time of its disappearance suggests a direct contribution to the elimination, but the 3'-exonuclease function of the polymerase is not needed. While DNA elimination is a surprising function for DNA polymerase, its use to restrict paternal genomes provides a strategy that cannot easily be evaded by the mitochondrial genome without compromising its replication.