THE FATE OF HUMAN SPERM-DERIVED MTDNA IN SOMATIC-CELLS

Inheritance of animal mtDNA is almost exclusively maternal, most likel y because sperm-derived mitochondria are actively eliminated from the ovum, either at or soon after fertilization. How such elimination occu rs is currently unknown. We asked whether similar behavior could be de tected in somatic cells, by following the fate of mitochondria and mtD NAs after entry of human sperm into transformed cells containing mitoc hondria but lacking endogenous mtDNAs (rho(0) cells). We found that a high proportion (10%-20%) of cells contained functioning sperm mitocho ndria soon after sperm entry. However, under selective conditions perm itting only the survival of cells harboring functional mtDNAs, only si milar to 1/10(5) cells containing sperm mitochondria survived and prol iferated. These data imply that mitochondria in sperm can enter somati c cells relatively easily, but they also suggest that mechanisms exist to eliminate sperm-derived mtDNA from somatic cells, mechanisms perha ps similar to those presumed to operate in the fertilized oocyte.