Mammalian fertilization:: From sperm factor to phospholipase Cζ

In mammalian eggs, the fertilizing sperm evokes intracellular Ca2+ ([Ca2+](i)) oscillations that are essential for initiation of egg activation and embryonic development. Although the exact mechanism leading to initiation of [Ca2+](i) Oscillations still remains unclear, accumulating studies suggest that a presently unknown substance, termed sperm factor (SF), is delivered from the fertilizing sperm into the ooplasm and triggers [Ca2+](i) oscillations. Based on findings showing that production of inositol 1,4,5-trisphosphate (IP3) underlies the generation of [Ca2+](i) oscillations, it has been suggested that SF functions either as a phospholipase C (PLC), an enzyme that catalyzes the generation of IP3, or as an activator of a PLC(s) pre-existing in the egg. This review discusses the role of SF as the molecule responsible for the production of IP3 and the initiator of [Ca2+](i) oscillations in mammalian fertilization, with particular emphasis on the possible involvement of egg- and sperm-derived PLCs, including PLCzeta a novel sperm specific PLC. (C) 2003 Elsevier SAS. All rights reserved.