The purpose of this project is to study the biological and biochemical processes involved in synthesizing and organizing the hyaluronic acid- rich extracellular matrix which surrounds most mammalian oocytes at the time of ovulation. This matrix is produced primarily by the approximately 1,000 cumulus cells which are initially closely adherent to the oocyte. In response to a gonadotropin surge these cells initiate hyaluronic acid synthesis and deposit it in the extracellular matrix. This process enlarges the cumulus cell-oocyte complex, and the fully expanded complex is ovulated approximately 10 hours later. We are studying this process with mouse cumulus cell-oocyte complexes in vitro. Three factors have been identified that are necessary for expansion: (1) a soluble factor produced by the oocyte which induces hyaluronic acid synthesis, (2) FSH (or cAMP) which amplifies the synthetic response, and (3) a factor in serum required to retain the newly synthesized hyaluronic acid in the matrix. We have shown that: a) the serum factor, identified by others as an inter-alpha-trypsin inhibitor, must be continuously present to maximize retention of newly synthesized hyaluronic acid in the matrix, b) decasaccharides but not octasaccharides of hyaluronic acid can displace the HA and prevent matrix formation, c) conversely, once formed decassacharides do not facilitate matrix disassembly, and d) an endogenously synthesized 45 kDa protein binds to the hyaluronic acid during matrix formation. Topics of present interest include: (1) identifying the factor produced by the oocyte that is required to induce hyaluronic acid synthesis, (2) determining how the cumulus cells respond to this factor via second messenger systems, (3) identifying the approximately 45 kDa protein by immunological and molecular biological probes, and (4) determining the role of this protein in matrix formation.
