ICSI choreography: fate of sperm structures after monospermic rhesus ICSI and first cell cycle implications

We have dissected the initial stages of fertilization by intracytoplasmic s perm injection of single spermatozoa into prime oocytes from fertile rhesus monkeys (Macaca mullata). DNA decondensation was delayed at the apical por tion of the sperm head. It is possible that this asynchronous male DNA deco ndensation could be related to the persistence of the sperm acrosome and pe rinuclear theca after injection, However, incomplete male pronuclear format ion did not prevent sperm aster formation, microtubule nucleation and pronu clear apposition, In contrast, DNA synthesis was delayed in both pronuclei until the sperm chromatin fully decondensed, indicating that male pronuclea r formation constitutes an important checkpoint during the first embryonic cell cycle.