Human round spermatids from azoospermic men exhibit oocyte-activation and Ca2+ oscillation-inducing activities.

During mammalian fertilization, intracellular Ca 2+ oscillations are important for both oocyte activation and embryonic development. As the ability of round spermatids (ROS) to induce Ca 2+ oscillations and oocyte activation is different between species, we examined Ca 2+ oscillation- and oocyte activation-inducing abilities of human ROS originating from patients with non-obstructive azoospermia. Human ROS from 11 non-obstructive azoospermic patients were collected during their TESE–ICSI cycles. Following injection into mature unfertilized mouse oocytes, we examined the oocyte-activating and Ca 2+ oscillation-inducing activities of ROS by using Ca 2+ imaging and confocal laser scanning microscopy (mouse test). In these 11 cases, clinical TESE–ICSI using mature testicular spermatozoa was successful, with the exception of one case in which only one sperm-injected oocyte was not fertilized. The mean fertilization rate was 70.1% (40–100%); the mean cleavage rate was 97.9% (46/47). Two pregnancies were established from 10 transfer cycles (PR; 20%). When the ROS from these patients were injected into mouse oocytes, the ROS from all patients induced at least some intracellular Ca 2+ oscillations (25–100%). In all patients, 40 out of 82 oocytes injected with ROS exhibited normal oscillation patterns of [Ca 2+ ]i. Human spermatogenetic cells acquired oocyte-activating and Ca 2+ oscillation-inducing abilities at the round spermatid stage, an earlier stage than found for rodent cells. These data indicate that human ROS might be useful for clinical treatments of non-obstructive azoospermic patients exhibiting mature spermatozoa in biopsied specimens.