Abstract
PURPOSE: Our purpose was to demonstrate the dynamics of the human sperm centrosome during fertilization and cleavage. METHODS: Human gametes, fertilized oocytes, and preimplantation embryos were examined by transmission electron microscopy. RESULTS: The functional sperm centrosome containing a typical centriole (proximal) is inherited at fertilization and forms a sperm monoaster. It then replicates and is perpetuated during cleavage. It organizes the mitotic apparatus at each stage of cleavage up to the hatching blastocyst stage. Bipolar spindles are formed in all monospermic and most dispermic embryos. Occasionally, two sperm asters and tripolar spindles are formed in dispermic embryos. Centrioles are associated with pronuclei and nuclei at interphases when they duplicate and occupy pivotal positions at spindle poles during mitoses. The maternal centrosome is not functional. CONCLUSIONS: The human embryo shows paternal centrosome inheritance and perpetuation like most other animals. Inheritance of defective centrosomes may lead to abnormal cleavage and contribute to infertility.