INTRACYTOPLASMIC SPERM INJECTION FOR RHESUS-MONKEY FERTILIZATION RESULTS IN UNUSUAL CHROMATIN, CYTOSKELETAL, AND MEMBRANE EVENTS, BUT EVENTUALLY LEADS TO PRONUCLEAR DEVELOPMENT AND SPERM ASTER ASSEMBLY

The disassembly and reorganization of sperm-derived structures are lan dmarks for the onset of embryonic development. Since complete informat ion on these events is not yet available, we examined the disassembly of the sperm axoneme, the formation of the sperm aster, and the decond ensation and development of the male and female pronuclei in inseminat ed Rhesus monkey oocytes conceived by in-vitro fertilization (IVF) or by intracytoplasmic sperm injection. During IVF, the spermatozoa lose their acrosomes after contacting the zona pellucida, and the plasma me mbrane and nuclear envelope disappear after fusion with the oolemma. S ubsequently, a sperm aster of microtubules forms around the proximal c entriole, which is bound to the sperm connecting piece. This process i s then followed by the formation of both pronuclei. The single sperm c entriole later duplicates and the bipolar mitotic apparatus is observe d. Following sperm injection, the spermatozoa have both an intact plas ma membrane and acrosome. Although the microtubules form the sperm ast er in a fashion identical to that seen during IVF, the presence of an intact acrosome appears to be associated with a heterogeneity in the d econdensation of sperm chromatin. While this may indicate an abnormal pattern of chromatin decondensation during the formation of the male p ronucleus following sperm injection, the male pronucleus eventually fu lly decondenses, as during NF. Sperm mitochondria are displaced as the sperm centriole is exposed. Annulate lamellae and a previously undesc ribed organelle which seems to contain annulate lamellae precursors, a s well as maternal mitochondria, are found in association with the dev eloping pronuclear envelopes. This information increases understanding of fertilization in primates, and may also be of significance for use in assisted human reproduction as well as in the preservation of enda ngered mammalian species. In addition, these results demonstrate the s imilarities between fertilization in Rhesus monkeys and humans, provid ing additional evidence for the use of this non-human primate as a mod el system in which to investigate the cellular and molecular biologica l basis of human reproduction.