The slow block to polyspermy as well as many other events that ensue after fertilization are elicited by the release of calcium, first at the site of sperm penetration, and then sweeping across the egg in a wave. The calcium wave can be visualized using fluorescent indicator dyes that fluoresce in response to local increases in intracellular calcium ion concentration. The pseudocolor footage provided here courtesy of Dr. Jerry Schatten (Oregon Health Sciences Univ) shows this calcium wave as changes in color. See if you can tell where the sperm entered the egg! The grayscale movie (provided by Dr. Mark Terasaki, Univ. of Connecticut), shows simultaneous visualization of the production of the fertilization envelope and the calcium wave. Notice that in this movie the calcium levels elevate in the same location as the first place where the fertilization envelope lifts off of the egg surface.
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| QuickTime movie of calcium dynamics (423K) | QuickTime movie of simultaneous fertilization envelope and calcium dynamics (2.3 Mb) |