Mitochondrial distribution and function in oocytes and early embryos.

Active mitochondria relocate during oocyte maturation or fertilization in several species. Detailed studies with hamster oocytes and early embryos reveal a pattern of active mitochondria migrating to surround the pronuclei to form a pattern that persists through the early cleavage stages. Although the functional significance of this relocation is unknown, it appears to be an important part of normal development in hamsters. Treatments that disrupt embryo development in vitro (such as the presence of inorganic phosphate or alteration of intracellular pH) also disrupt the normal pattern of mitochondrial distribution. Active mitochondria also reorganize during maturation in bovine oocytes and during fertilization in rhesus monkey oocytes. Examination of these changes in mitochondrial organization may provide insights into the regulation of normal embryo development and might serve as predictors of oocyte or embryo developmental competence.