Lysophosphatidylcholine induces changes in physicochemical, morphological, and functional properties of mouse zona pellucida: a possible role of phospholipase A2 in sperm-zona pellucida interaction.

Abstract

Previous evidence has suggested the implication of phospholipase A2 (PLA2) in the interaction of the sperm with the egg's zona pellucida (ZP). We have tested this hypothesis by observing the effect of one of the products of the enzyme reaction, namely lysophosphatidylcholine (LPC), on the functional, physicochemical and morphological properties of ZP. In vitro treatment of oocytes with LPC produced a dramatical increase in the ability of ZP to bind sperm. This increased binding was completely abolished if sperm were pre-treated with pertussis toxin to block the acrosome reaction. ZP was the primary target of LPC since the same effect occurred on isolated ZP. LPC treatment of isolated ZP also produced alterations in its physicochemical properties as deduced from both a decreased binding of fluorescent lectins and an increased solubility of ZP at low pH. As assessed by scanning electron microscopy, LPC also produced dramatic changes in the structure of the ZP surface which lost its typical rough aspect and became smooth. These morphological changes were observed upon LPC treatment of both the intact oocyte and the previously isolated ZP. The chemically related (and precursor molecule of LPC in PLA2 reaction) phosphatidylcholine (PC) had no effect on any of the above studied parameters. Most importantly, LPC had no effect on ZP from two-cell embryos, a structure that has physiologically become refractory to further sperm binding. Analysis of radioiodinated ZP proteins by SDS-PAGE did not indicate an important effect of LPC on these proteins, although the ZP3 protein seemed to be slightly more iodinated.