Activity of a sperm-borne oocyte-activating factor in spermatozoa and spermatogenic cells from cynomolgus monkeys and its localization after oocyte activation

it is widely accepted that mature mammalian oocytes are induced to resume m eiosis by a sperm-borne oocyte-activating factor(s) (sperm factor, SF) imme diately after normal fertilization or intracytoplasmic sperm injection. The SF is most likely a soluble factor that is localized within the cytoplasm of mature spermatozoa, but the exact stage at which it appears during sperm atogenesis and its localization after oocyte activation is not fully unders tood, except in the mouse. First, we injected mature spermatozoa and sperma togenic cells from cynomolgus monkeys into mouse oocytes to assess their oo cyte-activating capacity. More than 90% of mouse oocytes were activated aft er injection of monkey spermatozoa. Round spermatids and primary spermatocy tes (late pachytene to diplotene) also activated oocytes (93% and 79%, resp ectively). injection of monkey spermatozoa and spermatids induces intracell ular Ca2+ oscillations in a pattern similar to that seen following normal f ertilization. Most spermatocytes did not produce typical intracellular Ca2 oscillations. Second, we transferred pronuclei or cytoplasts from mouse oo cytes that had been activated by monkey spermatozoa or spermatids into inta ct mature mouse oocytes by electrofusion in order to examine the localizati on of the SF after pronuclear formation. Some of the SF was localized withi n the pronuclei, but some stayed in the ooplasm. This study demonstrated th at spermatogenic cells of cynomolgus monkeys acquire oocyte-activating capa city at much earlier stages than those of mice, and that the monkey SF has a pronucleus-directing nature, although to a lesser extent than the mouse S F.