Figure 4.

Cycle of Ca²⁺ transient generation in mammalian eggs at fertilization. Starting at the top left, the large grey arrows show temporal order. For each panel, the cytoplasmic Ca²⁺ trace is coloured orange at the portions of the trace that are generated mainly due to the steps illustrated in that panel. Top left: Sperm PLCζ acts on PIP2 in intracellular vesicles to generate IP3, which stimulates IP3R-mediated Ca²⁺ release and subsequent Ca²⁺-induced Ca²⁺ release. Top right: Ca²⁺ stimulates mitochondrial ATP production; ATP is required for SERCA pump activity. Bottom right: Ca²⁺ is pumped back into the ER through SERCA pumps and out of the egg through PMCA pumps and NCX. Bottom left: Ca²⁺ flows into the cytoplasm through TRMP7, Ca_V3.2 and TRPV3 channels and is then available for SERCA pumps to replenish ER Ca²⁺ stores in preparation for the next Ca²⁺ release event. Orange dots indicate Ca²⁺ at its destination; small grey arrows show the direction of flow. Ca_V3.2, T-type voltage-dependent Ca²⁺ channel; IP3, inositol trisphosphate; IP3R, IP3 receptor; MCU, mitochondrial uniporter; NCX, sodium/Ca²⁺ exchanger; PIP2, phosphatidylinositol 4,5-bisphosphate; PLCζ, phospholipase C zeta; PMCA, plasma membrane Ca²⁺ ATPase; SERCA, sarco/endoplasmic reticulum Ca²⁺ ATPase pump; TRPM7, transient receptor potential cation channel subfamily M member 7; TRPV3, transient receptor potential cation channel subfamily V member 3.