Spermatozoon is the male gamete. After ejaculation this cell is not mature, so it can not fertilize the oocyte.  To have the ability to fertilize the female gamete, this cell suffers capacitation and acrosome reaction in female reproductive tract. The signaling pathways best described for spermatozoon involve these processes.  The cAMP/PKA signaling pathway leads to sperm cells capacitation; however, adenylyl cyclase in sperm cells is different from the somatic cells. Adenylyl cyclase in spermatozoon does not recognize G proteins, so it is stimulated by bicarbonate and Ca ions. Then, it converts adenosine triphosphate into cyclic AMP, which activates Protein kinase A. PKA leads to protein tyrosine phosphorylation.
Phospholipase C (PLC) is involved in acrosome reaction. ZP3 is a glycoprotein present in zona pelucida and it interacts with receptors in spermatozoon. So, ZP3 can activate G protein coupled receptors and tyrosine kinase receptors, that leads to production of PLC. PLC cleaves the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) into diacyl glycerol (DAG) and inositol 1,4,5-trisphosphate. IP3 is released as a soluble structure into the cytosol and DAG remains bound to the membrane. IP3 binds to IP3 receptors, present in acrosome membrane.  In addition, calcium and DAG together work to activate protein kinase C, which goes on to phosphorylate other molecules, leading to altered cellular activity. These actions cause an increase in cytosolic concentration of Ca that leads to dispersion of actin and consequently promotes plasmatic membrane and outer acrosome membrane fusion.
Progesterone is a steroid hormone produced in cumulus oophorus. In somatic cells it binds to receptors in nucleus; however, in spermatozoon its receptors are present in plasmatic membrane. This hormone activates AKT that leads to activation of other protein kinases, involved in capacitation and acrosome reaction.
When ROS (reactive oxygen species) are present in high concentration, they can affect the physiology of cells, but when they are present in moderated concentration they are important for acrosome reaction and capacitation. ROS can interact with cAMP/PKA and progesterone pathway, stimulating them. ROS also interacts with ERK pathway that leads to activation of Ras, MEK and MEK-like proteins. These proteins activate protein tyrosine kinase (PTK) that phosphorylates various proteins important for capacitation and acrosome reaction.