Insights into the Molecular Mechanisms Involved in Sea Urchin Fertilization Envelope Assembly

Sea urchin fertilization envelope assembly provides an ideal model system for investigating the production and modification of an extracellular matrix. The contents of secretory vesicles and the egg glycocalyx mix to initiate assembly. Limited proteolysis and covalent crosslinking by a transglutaminase act as early events to modify the nascent envelope. A subset of secreted proteins binds to this matrix through ionic interactions that require divalent cations. For example, one secreted protein, proteoliaisin, is responsible for attaching ovoperoxidase to the envelope. Ovoperoxidase hardens the envelope by using hydrogen peroxide, produced by the egg during the respiratory burst, to form dityrosine crosslinks between a subset of fertilization envelope proteins. Numerous spatial and temporal regulatory mechanisms exist to ensure that proper assembly occurs in an environment isolated from the normal cytosolic regulatory machinery.