P-Tyr-containing proteins in the egg cortex overlying the decondensing sperm head. Samples prepared as in Fig. 1 were stained with anti-P-Tyr followed by Alexa-488-goat anti-mouse IgG (green) and Hoechst 33258 (white) to label DNA. Fertilizing (capacitated) sperm bound to the oolema exhibited P-Tyr proteins in the sperm mid-piece, however specific P-Tyr label was not detected in the head region (Panel A). As fertilization progressed, decondensing sperm heads located deep to the oolema were associated with an increase in P-Tyr-containing proteins within the egg cortex immediately overlying the sperm nucleus (Panel B, C and D). Occasionally, the male pronucleus formed and remained adjacent to the egg cortex for some time and the P-Tyr label continued to be detected in the cortex near the paternal chromatin (Panel E). As the sperm DNA migrated away from the cortex, the P-Tyr label disappeared (not shown). Magnification is indicated by the bar which represents 10μm.