Purification, characterization, and molecular cloning of an outer layer protein of carp fertilization envelope

An outer layer protein of carp fertilization envelope (FE), FEO-1, was purified from carp oocytes. The cDNAs encoding FEO-1 were cloned. The mature protein of FEO-1 is 21 kDa in molecular weight and contains 177 amino acid residues whose sequence has 58% identity to the outer layer protein of chick vitelline membrane. In situ hybridization and immunocytochemistry show that FEO-1 is expressed in oocytes and liver. In oocytes, FEO-1 is stored in the cortical granules. During cortical reaction, it is exocytosed to the perivitelline space and then gradually added to the outer layer of FE (FE(o)). FEO-1 first appears as discrete deposits along FE(o), then merges to form a continuous layer. The thickness of FE(o) increases as cortical reaction proceeds. In addition to FEO-1, FE(o) contains cystatin, fibroin-like substance (FLS), and cathepsin-like substance (CLS) as well. They are stored in the cortical granules and are exocytosed to FE(o) simultaneously with FEO-1 during cortical reaction. In FE(o), FEO-1 is present in monomer form and can be completely extracted by sodium dodecyl sulfate (SDS)-mercaptoethanol (MSH). On the other hand, the cystatin, FLS, and CLS present in FE(o)are cross-linked together. They are partially extracted by SDS-MSH but can be completely extracted by guanidium thiocyanate-lauroylsarcosine.