The activity (calcium oscillator?) responsible for human oocyte activationafter injection with round spermatids is associated with spermatid nuclei

Objective: To compare the oocyte-activating ability of whole human round sp ermatids and their isolated nuclei. Design: Prospective study using sibling oocytes from patients undergoing sp ermatid conception and intracytoplasmic sperm injection treatment cycles. Setting: Private assisted reproduction laboratories and a university depart ment. Patient(s): Couples with male infertility. Intervention(s): Sibling oocytes were injected either with whole round sper matids or with their isolated nuclei, followed by artificial triggering of oocyte activation with calcium ionophore. Other sibling oocytes were inject ed either with isolated spermatid cytoplasm or with whole mature spermatozo a. Main Outcome Measure(s): Numbers of activated oocytes and cleaving embryos. Result(s): After oocyte activation was boosted with calcium ionophore, whol e spermatids and isolated spermatid nuclei were equally effective in suppor ting oocyte activation and the formation of pronuclei, whereas no control o ocyte was activated under the same conditions after injection of isolated s permatid cytoplasmic compartments. Cleavage rates were lower after the inje ction of isolated spermatid nuclei than after the injection of whole sperma tids. Conclusion(s): The factor responsible for human oocyte activation after rou nd spermatid injection is associated with spermatid nuclei. The requirement for the artificial trigger (calcium ionophore) suggests that this factor i s identical to the male gamete activity previously characterized as calcium oscillator. (Fertil Steril(R) 2000;74:1245-7. (C) 2000 by American Society for Reproductive Medicine).