Fertilization and early embryology: Progesterone-induced acrosome reaction: potential role for sperm acrosome antigen-1 in fertilization

We have established a monoclonal antibody (mAb) AG7 defininga sperm acrosome antigen-1 (SAA-1) on spermatozoa from the humanand several mammalian species. MAb AG7 inhibits fertilizationof mouse eggs in vitro and in vivo. An important characteristicof mAb AG7 is its inhibition of the rise in intracellular calciuminduced by progesterone in human spermatozoa. Here we show that,following the acrosome reaction, SAA-1 is lost from the capof human spermatozoa but remains detectable in the equatorialregion. Acrosome reaction assays demonstrated a clear differencebetween progesterone- and A23187-induced acrosome reactions.For induction of the acrosome reaction with progesterone, aminimum capacitation time of 6 h was required. A23187 inducedthe acrosome reaction regardless of capacitation time. MAb AG7completely inhibited the progesterone-induced acrosome reaction,but not the A23187-induced acrosome reaction in human spermatozoa.Differences in the pattern of calcium flux induced by the twoagents might account for this phenomenon. The inhibition ofthe progesterone-induced acrosome reaction by mAb AG7 impliesa regulatory function of SAA-1 during the human sperm acrosomereaction.