Fig. 2. Immunofluorescent microscopic visualization of localized tyrosine phosphorylation in fertilized and H₂O₂-treated Xenopus eggs. Sections (10 µm) of Xenopus unfertilized eggs (A,B,G,H), fertilized eggs (C-F,I,J; 5 minutes after insemination), A23187-treated eggs (K,L; 0.5 µM, 5 minutes), or H₂O₂-treated eggs (M,N; 10 mM, 5 minutes) were immunostained with anti-phosphotyrosine antibody (PY99, 1 µg/ml). The samples were analyzed by confocal laser-scanning microscopy (model LSM410, Zeiss, Germany). Indirect immunostained images obtained with fluorescein isothiocyanate (FITC) and the corresponding Nomarski cell images are shown. White arrowheads in C indicate the area showing fertilization-dependent tyrosine phosphorylation. Scale bars: 250 µm in A-F,K-N; 62.5 µm in G-J.