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Organizing the Egg Matrix

Prior to ovulation, an expanded extracellular matrix forms around the mammalian oocyte. This cumulus oophorus matrix is essential for female fertility and consists of a mesh-like network of hyaluronan. Previous studies have shown that three molecules are essential for the proper organization of hyaluronan in this matrix: inter--trypsin inhibitor (II, a serum macromolecule that enters the follicle prior to ovulation) and two proteins synthesized by the cumulus cells surrounding the oocyte, tumor necrosis factor-induced protein 6 (TNFIP-6, a hyaluronan-binding protein) and pentraxin 3 (PTX3, a protein that forms pentamers). II is a complex macromolecule consisting of a chondroitin sulfate chain on bikunin, a trypsin inhibitor, and two proteins, referred to as heavy chains, covalently bound directly to the chondroitin sulfate. TNFIP-6 has been shown to be required to transfer heavy chains from II onto hyaluronan.

A model for the assembly of the cumulus matrix.

In this Paper of the Week, Laura Scarchilli and colleagues now show that heavy chains of II interact with the N-terminal domain of PTX3 and that this portion of PTX3 is required and sufficient for organizing the hyaluronan matrix. These results suggest that direct interactions between pentameric PTX3 and the heavy chains on hyaluronan are necessary to form the matrix around the oocyte that is essential for ovulation and for successful in vivo fertilization.

FOOTNOTES

See referenced article, J. Biol. Chem. 2007, 282, 30161-30170

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