Kinetics of the Progesterone-Induced Acrosome Reaction and Its Relation to Intracellular Calcium Responses in Individual Human Spermatozoa1

Abstract

Progesterone at 3 microM triggers a biphasic (transient and sustained) increase in intracellular calcium ([Ca(2+)](i)) in human sperm, which is believed to be a prerequisite for progesterone-induced acrosome reaction (AR). As very little is known about how AR occurrence, latency, and completion relate to the characteristics of the progesterone-induced [Ca(2+)](i) signal, we examined these events using fluorescence microscopy of individual living human sperm. Direct assessment of acrosomal status after calcium imaging showed no differences in kinetics or amplitude of the preceding progesterone-induced calcium responses in acrosome-reacted and acrosome-intact cells, which indicates that the amplitude of the [Ca(2+)](i) signal is not the critical determinant of AR. Chelation of extracellular calcium to arrest AR at varying times after progesterone stimulation revealed that maximal AR occurred immediately following progesterone stimulation, during the initial transient calcium influx rather than during the sustained calcium response. Attempts to follow acrosomal dispersal in real-time by staining with the acidic organelle probes LysoTracker DND-99 and dapoxyl (2-aminoethyl) sulphonamide (DAES) proved inconclusive due to heterogeneous labeling of the cell population. Surprisingly, the dye was often not confined to the acrosome but stained the whole sperm head, which suggests that only a subpopulation of human sperm cells contains a sufficiently acidic acrosome.

Ca 2+ Signaling Tools Acquired from Prostasomes Are Required for Progesterone-Induced Sperm Motility

“…4C). Progesterone has been reported to stimulate the acrosome reaction (AR), a process that allows the sperm to bind and fuse with the egg membrane, through a mechanism involving calcium mobilization (34,35). As previously reported (34), we found that progesterone promoted the AR in PFS but not NFS ( fig.…”

Dynamic resolution of acrosomal exocytosis in human sperm

“…1A). Preliminary analyses on the kinetics of antibody binding to acrosome-reacted sperm (using 10 μM A23187 to pre-induce the AR) (Harper et al, 2006;Jamil and White, 1981; An essential step in mammalian fertilisation is the sperm acrosome reaction (AR) -exocytosis of a single large vesicle (the acrosome) that surrounds the nucleus at the apical sperm head. The acrosomal and plasma membranes fuse, resulting in both the release of factors that might facilitate penetration of the zona pellucida (which invests the egg) and the externalisation of membrane components required for gamete fusion.…”

“…To understand how the AR facilitates progression of the sperm through the zona pellucida by proteolytic activity and also exposes the IAM such that gamete fusion occurs, the details of the process must be observed in live cells. Attempts to visualise exocytosis by monitoring membrane loss in live human sperm have proved unsuccessful (Harper et al, 2006), but fluorescent tagging of acrosomal content in macaque sperm suggests a possible approach (Tollner et al, 2003). Here, we uncover the events of the AR in real time in live human sperm.…”

“…1E). Stimulation with progesterone, a product of the cumulus oophorus (Hartshorne, 1989;Osman et al, 1989), at a dose of 3 μM [similar to concentrations within the cumulus and widely reported to induce AR in human sperm (Harper et al, 2006;Kirkman-Brown et al, 2000;Osman et al, 1989)], induced AR in 10% of sperm. The kinetics of fluorescent anti-CD46 uptake under these conditions were significantly slower than in A23187-treated sperm (P<0.05; Fig.…”

Hyperactivation of Stallion Sperm Is Required for Successful In Vitro Fertilization of Equine Oocytes1

“…We have also observed this in stallion sperm (data not shown). However, calcium is also a critical component of the pathways regulating protein tyrosine phosphorylation and acrosomal exocytosis [50][51][52][53]. One might argue that procaine facilitated IVF through the activation of these pathways.…”