Fission yeast cells mix parental mitochondria in a progressive manner during meiosis

Mitochondria in many fungi are inherited uniparentally during meiosis. It has remained unclear whether parental mitochondria in the fission yeast Schizosaccharomyces pombe are inherited uniparentally or biparentally. Here, we assessed the mixing of parental mitochondria carefully by live-cell microscopy and developed an algorithm to determine the degree of mitochondrial mixing in a quantitative manner. We found that parental mitochondria in fission yeast cells were mixed progressively as meiosis progressed. Moreover, we established that mitochondrial fission and the size of the conjugation neck are the limiting factors in restricting the mixing of parental mitochondria. We further employed a combination of quantitative polymerase chain reaction, fluorescent live-cell microscopy, and transmission electron microscopy approaches to examine the mitochondrial inheritance of progeny cells derived from a cross between wild-type and Rho0 (mitochondrial DNA absent) cells. The results show that all progeny cells of the cross carry mitochondrial DNA. Hence, our data support the model in which parental mitochondria in the fission yeast S. pombe are inherited biparentally during meiosis.