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

OBJECTIVE To compare the oocyte-activating ability of whole human round spermatids and their isolated nuclei. DESIGN Prospective study using sibling oocytes from patients undergoing spermatid conception and intracytoplasmic sperm injection treatment cycles. SETTING Private assisted reproduction laboratories and a university department. PATIENT(S) Couples with male infertility. INTERVENTION(S) Sibling oocytes were injected either with whole round spermatids or with their isolated nuclei, followed by artificial triggering of oocyte activation with calcium ionophore. Other sibling oocytes were injected either with isolated spermatid cytoplasm or with whole mature spermatozoa. MAIN OUTCOME MEASURE(S) Numbers of activated oocytes and cleaving embryos. RESULT(S) After oocyte activation was boosted with calcium ionophore, whole spermatids and isolated spermatid nuclei were equally effective in supporting oocyte activation and the formation of pronuclei, whereas no control oocyte was activated under the same conditions after injection of isolated spermatid cytoplasmic compartments. Cleavage rates were lower after the injection of isolated spermatid nuclei than after the injection of whole spermatids. CONCLUSION(S) The factor responsible for human oocyte activation after round spermatid injection is associated with spermatid nuclei. The requirement for the artificial trigger (calcium ionophore) suggests that this factor is identical to the male gamete activity previously characterized as calcium oscillator.