Lipid levels in sperm, eggs, and during fertilization in Xenopus laevis

Douglas W Petcoff,Bradley J Stith,William L Holland

doi:10.1194/jlr.m800159-jlr200

Douglas W Petcoff, Bradley J Stith + Show 1 more

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https://doi.org/10.1194/jlr.m800159-jlr200

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Abstract

Critical developmental periods, such as fertilization, involve metabolic activation, membrane fusion events such as sperm-egg or plasma membrane-cortical granule merger, and production and hydrolysis of phospholipids. However, there has been no large-scale quantification of phospholipid changes during fertilization. Using an enzymatic assay, traditional FA analysis by TLC and gas chromatography, along with a new method of phospholipid measurement involving HPLC separation and evaporative light-scattering detection, we report lipid levels in eggs, sperm, and during fertilization in Xenopus laevis. Sperm were found to contain different amounts of phospholipids as compared with eggs. During fertilization, total phosphatidylinositol, lysophosphatidylcholine, sphingomyelin, and phosphatidylserine decreased, and ceramide increased, whereas there was no change in phosphatidylcholine, cardiolipin, or phosphatidylethanolamine. FA analysis of phospholipids found numerous changes during fertilization. Because there is an increase in sn-1,2-diacylglycerol at fertilization, the FAs associated with this increase and the source of the increase in this neutral lipid were examined. Finally, activation of phospholipase C, phospholipase D, phospholipase A2, autotoxin, and sphingomyelinase at fertilization is discussed.

Highlights

Critical developmental periods, such as fertilization, involve metabolic activation, membrane fusion events such as sperm-egg or plasma membrane-cortical granule merger, and production and hydrolysis of phospholipids
Because choline mass increases on a magnitude equivalent to the increase in DAG, we suggested that breakdown of PC by phospholipase D (PLD) is the source of DAG [9]
Using our new method of phospholipid analysis by HPLC and evaporative light-scattering detection (ELSD), sperm were found to contain a very different ratio of phospholipids than that found in eggs (Fig. 1)

Summary

Introduction

Critical developmental periods, such as fertilization, involve metabolic activation, membrane fusion events such as sperm-egg or plasma membrane-cortical granule merger, and production and hydrolysis of phospholipids. Membrane bending and fusion are associated with the acrosome reaction of sperm (wherein the large sperm acrosome undergoes exocytosis upon interaction with layers that cover the egg), with sperm-egg merger, and with subsequent fertilization events such as cortical granule exocytosis [10, 11]. Both Xenopus and human eggs are arrested in meiosis II [12].

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