STRUCTURE AND FATE OF PATERNAL MITOCHONDRION DURING EARLY EMBRYOGENESIS OF PARACENTROTUS LIVIDUS

Soon after entrance of the spermatozoon into the ooplasm, the intact middle piece separates from the male nucleus and appears in a central region of the egg. Because of its large size, complex cristae arrangement, and pronounced density, the sperm mitochondrion is distinguishable from the smaller, typical egg mitochondria. During the early stages of embryogenesis, the egg mitochondria surround and contact the intact sperm mitochondrion. At later stages, particularly after the first cleavage division, the sperm mitochondrion appears to undergo a progressive degradation and resorption. Sperm mitochondria surround portions of the ribosome-rich ooplasm; dissolution of mitochondrial matrix, swelling of mitochondrial compartments, and disruption of the cristae commence in regions adjacent to the circumscribed ooplasmic compartment. Mitochondria of sperm seem to disintegrate by a process of self-autolysis suggesting that the paternal mitochondrion affects no prolonged influence on embryogenesis. © 1968 Academic Press Inc.