Adenophostin, a potent agonist of the inositol 1,4,5-trisphosphate receptor, is useful for fertilization of mouse oocytes injected with round spermatids leading to normal offspring

Abstract

Precursor male gametes such as round spermatids and secondary spermatocytes are known to possess the potential to achieve fertilization and embryonic development when injected into mature oocytes, but in previous studies, injected mouse spermatids did not activate the oocytes. In this study, we confirmed that this was the case because spermatids by themselves could not induce an increase in intracellular Ca2+ concentration ([Ca2+](i)) of oocytes, the pivotal signal in oocyte activation. Repetitive rises in [Ca2+](i) (Ca2+ oscillations), lasting for at least 3 h as observed at fertilization, were produced by a single injection of adenophostin B isolated from fungal products, a novel nonmetabolizable agonist of the inositol 1,4,5-trisphosphate receptor (InsP3r), which mediates Ca2+ release from the endoplasmic reticulum. Ca2+ oscillations were blocked by an antibody against the type 1 InsP3r. About 95% of oocytes were activated by adenophostin (0.3-0.4 μM in the oocyte). Simultaneous injection of a round spermatid and adenophostin resulted in 55% fertilization success in association with male and female pronucleus formation and development to two-cell embryos. Furthermore, 25% of two-cell embryos that were transplanted to foster mothers developed to normal offspring. All infants grew into adults that reproduced healthy second generations. Adenophostin will be useful for parthenogenetic oocyte activation in the biotechnology of animal reproduction. Injection combined with precursor spermatozoa may be applicable to assisted conception therapy for patients with defective spermatogenesis.