Mode of Mitochondrial Formation in HeLa Cells

The mode of mitochondrial formation has been so far directly investigated only in Neurospora crassa. By using a choline-requiring mutant of this organism, Luck (1963, 1965) has obtained evidence which strongly suggests that mitochondria are formed by growth and division of preexisting mitochondria. In Tetrahymena pyriformis (Parsons and Rustad, 1968), the distribution of long-term [^(3)H]thymidine-labeled mitochondrial DNA among mitochondria during growth in unlabeled medium, as studied by autoradiography, has been found to follow a pattern compatible with this mode of mitochondrial formation. In animal cells, no evidence presently exists regarding the mode of mitochondrial formation, apart from electron micrographs of structures which have been interpreted as mitochondrial fission figures (e.g. Tandler et al., 1969; Larsen, 1970)