Mouse cPLA2γ, a novel oocyte and early embryo-abundant phospholipase A2 gamma-like protein, is targeted to the nuclear envelope during germinal vesicle breakdown

Abstract

Abstract This report documents the characterization of a novel mouse oocyte protein which was originally identified by microsequence analysis of a 67.8 kDa protein spot (pI 5.7) on a Coomassie-stained two-dimensional (2D) gel of murine egg proteins. Tandem mass spectroscopic analysis of the peptides obtained from the cored protein yielded sequences that appeared to match only ovary, egg, and preimplantation embryo cDNAs. We then cloned the novel gene by RACE-PCR, and analysis of the deduced cDNA sequence found that this maternal product was 56% identical to human cytosolic phospholipase A2? (cPLA2?). Based on this sequence homology, we named the molecule mouse cytosolic phospholipase A2? (cPLA2?). As with human cPLA2?, mouse cPLA2? contains a lipase consensus sequence and lacks the calcium binding domain that is found in other PLA2 proteins. However, mouse cPLA2? is different from human cPLA2? in that mouse cPLA2? expression is restricted to the ovary and that the protein does not contain the myristoylation and prenylation lipid-anchoring motifs that are present in human cPLA2?. Within oocytes, mouse cPLA2? localizes mainly to the oocyte cortex and to the nucleoplasm. Interestingly, during germinal vesicle breakdown, mouse cPLA2? aggregates dynamically relocate from the oocyte cortex to the nuclear envelope, suggesting a possible role for this putative egg-restricted phospholipase A2? in membrane remodeling. Furthermore, mouse cPLA2? protein continues to be expressed in the embryo until the 4-8-cell stage of development, suggesting that mouse cPLA2? may function as a previously uncharacterized maternal effect gene. Keywords: cPLA2?; Maturation; Fertilization; Preimplantation