Regulation of Cellular Interactions by Extracellular Matrix Proteolysis

University Of California-Davis, Davis CA

Investigators

Abstract

0111285 Lindsay The extracellular egg envelope plays a crucial role in regulating sperm-egg interactions both before and after fertilization, and is thus a major subject of interest in developmental biology. After initial sperm penetration and fertilization, the egg envelope is modified by egg factors to defend the egg against sperm to prevent polyspermy, a condition that is lethal to embryonic development. During this complex "block to polyspermy" reaction, sperm binding sites on the egg envelope are inactivated, and the envelope structure is modified so that it is "hardened" to impede sperm penetration and to protect the developing embryo. These observations are almost a century old but still the mechanisms behind the reactions are unknown, due primarily to the lack of biological material, especially in mammals. One hypothesis is that an egg protease is involved in the reaction, since proteolysis of a specific egg envelope glycoprotein, ZPA, has been observed following fertilization. The current research project is designed to test this hypothesis by isolating and characterizing the responsible egg protease, designated "ZPAase", followed by the determination of its effects on egg envelope physical properties and function. The amphibian model system Xenopus laevis is used due to the large amounts of gametes that are available for study. Previously funded research identified ZPAase as a metalloprotease and it was partially purified. Continuing studies will complete the purification of ZPAase, and use molecular cloning techniques to determine the amino acid sequence of ZPAase for functional information and comparison to other proteases. Purified protease, obtained from eggs or through protein expression, will be used test the hypothesis of ZPA proteolysis on sperm binding to the egg envelope and envelope hardening. The results of these studies will make a significant contribution to our knowledge of the complex reactions that regulate sperm-egg interactions following fertilization and are fundamental to normal animal development.