Secretion of epitope-tagged mZP3, mutated at its CFCS, by growing mouse oocytes. Flag-mZP3-Myc and Δ-Flag-mZP3-Myc (mutated at its CFCS) were microinjected into growing oocytes isolated from 14- to 15-d-old mice. Oocytes were cultured for ∼20 h and then stained with either anti-Flag or anti-Myc, followed by FITC-conjugated secondary antibody. Intense fluorescence was evident over the plasma membrane/ZP region of oocytes injected with either cDNA construct after staining with anti-Flag (A and B) but not with anti-Myc (C and D). It was noted that, in almost all instances, there was a larger accumulation of fluorescently labeled vesicles in oocytes microinjected with Δ-Flag-mZP3-Myc (B and D) than in oocytes microinjected with Flag-mZP3-Myc (A and C). In each case, 100–200 oocytes were examined by LSCM. Bar (B), 10 μm.