In human spermatozoa acrosome reaction and hyperactivation, two important fertilization events, are regulated by free calcium ion concentration in cell cytosol. Both of those events can be induced by progesterone, a steroid hormone which indirectly activates CatSper. CatSper is a cation channel located in sperm flagella; calcium ions enter cytosol through the open channel and then diffuse into spermatozoon midpiece, where a specific isoform of phospholipase C, PLCδ, is located. Activity of this enzyme is upregulated by calcium concentration rise; PLCδ catalyzes inositole-1,4,5-triphosphate production from a membrane phospholipid phosphatidylinositol 4,5-bisphosphate. IP3 activates IP3 channel-receptors located on the spermatozoon calcium store, redundant nuclear envelope (RNE), and thus induces calcium release into cell cytoplasm through those receptors.
spermatozoa, calcium signaling, mathematical modeling, progesterone
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