Major vitelline envelope proteins in pipefish oocytes originate within the follicle and are associated with the Z3 layer

A method is described for purifying salt‐washed vitelline envelopes of pipefish eggs. Approximately 72% of the envelope dry weight is represented by 2 extractable proteins with molecular masses of 109 and 98 kDa. The 2 proteins are present in a 1:2 ratio, respectively, on 1‐dimensional electrophoretic gels; the 98 kDa protein can be resolved further into a family of peptides by 2‐dimensional gel electrophoresis. A monoclonal antibody raised against vitelline envelope protein recognizes both groups of protein and no other component of the oocyte, plasma, or liver. Immunocytochemistry indicated that the recognized antigen first appears in late cortical alveolistage oocytes, coincident with formation of the Z3 layer of the vitelline envelope; immunogold staining of thin sections confirmed antigen localization to the Z3 layer. Incubation of intact follicles with [ 35 S]methionine in vitro followed by 2‐dimensional gel electrophoresis and immunoblotting demonstrated the synthesis of the vitelline envelope proteins by such preparations. However, isolated follicle cells or denuded oocytes failed to yield convincing evidence of a similar nature. We conclude from these observations that the principal vitelline envelope proteins originate from within the follicle rather than elsewhere, such as the liver, and that the structural integrity of the follicle may be necessary for their elaboration.