Sperm integrity is critical for normal mitotic division and early embryonic development

The human zygote relies on the paternal gamete to provide the centrosome co mponent essential for the first mitotic division. It is not known whether n ormal centrosome function requires an intact spermatozoon, or whether donat ion of an isolated paternal centrosome component can result in normal zygot es and embryos. To explore this possibility, mature human oocytes were micr oinjected with either intact or dissected spermatozoa. Fertilization and cl eavage rates were documented; nuclear and cytoskeletal changes were observe d with fluorescent immunocytochemistry; and chromosomal normality was asses sed with fluorescent in-situ hybridization. A pilot study was performed to identify cytoskeletal features suggestive of centrosome function. Unfertili zed oocytes and tripronucleate (3PN) zygotes from in-vitro fertilization or intracytoplasmic sperm injection were assessed to confirm the sequence of the landmarks of human fertilization. Oocytes injected with mechanically-di ssected spermatozoa appear to be capable of normal pronuclear formation and embryonic cleavage, but do not undergo normal mitotic division. Although d econdensed, apposed nuclei are noted in combination with diffuse cytoskelet on assembly, no spindle was detected in any zygote resulting from the injec tion of a dissected spermatozoon. Analysis of selected embryos resulting fr om dissected sperm injection revealed chromosomal mosaicism in the majority of specimens. The lack of a bipolar spindle, in combination with chromosom al mosaicism, suggests abnormalities of the mitotic apparatus when sperm in tegrity is impaired following dissection.