Sea urchin C. elegans Human Node N° of links Node N° of links Node N° of links [Ca2+]i 19 [Ca2+]i 10 Ca2+ 26 cGMP 15 [H+]i 9 APT/ADP 16/8 [H+]i 14 Motility 8 Protein tyrosine phosphorilation 14 cAMP 13 ATP 7 PKA 9 ATP 9 Vesicle fusion 7 PLD1 8     NADH 7

Table 5: Most connected nodes (hubs) in sea urchin, C. elegans and human spermatozoa activation network.