Movies of Fertilization Processes

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Vitelline membrane elevation in sea urchin fertilization

This movie, downloaded from Bill Wasserman's Developmental Biology Page, clearly shows sperm being lifted away from the oocyte plasma membrane as the perivitelline space volume increases in the slow block to polyspermy. From BW's DBP:

"The transient increase in calcium in the newly fertilized egg, causes the exocytosis of the cortical vesicles. The released contents of the cortical vesicles into the perivitelline space causes the elevation of the vitelline membrane, now called the fertilization membrane, away from the surface of the egg. This biochemically hardened membrane now acts as a slow physical block to polyspermy. I think the sperm enters the egg at the 7 o'clock position?"

   
Calcium wave in a frog egg injected with Ip3

This movie, showing the progression of a Ca++ wave across a frog egg, was morphed by from still images by Jeff Hardin (Dept. of Zoology, U. Wisconsin). The original still images were obtained by loading an unfertilized Xenopus egg with a Ca++-sensitive dye and monitoring fluorescence intensity after injecting the egg with IP3 (Larabell, C. and Nuccitelli, R., 1992. Inositol lipid hydrolysis contributes to the Ca wave in the activating egg of Xenopus laevis. Dev. Biol. 153: 347-355). Note that the wave sweeps from the injection point at ~2 O'clock. This shows the fundamental role of IP3 in releasing Ca++ from intracellular stores as part of the slow block to polyspermy. From Hardin's Amphibian Development Tutorial:

"Egg activation in most species is thought to involve a series of similar signal transduction steps after sperm binds to a receptor protein on the egg/oocyte surface. One of the steps that is thought to be crucial for subsequent release of calcium from internal stores (typically, the endoplasmic reticulum, or ER) is the production of inositol triphosphate (IP3) from PIP2 residing in the egg plasma membrane. The cleavage of PIP2 into IP3 and diacylglycerol (DAG) results in numerous "downstream" events ‹ IP3 is thought to stimulate local release of calcium ions from the ER, resulting in the "calcium activation wave" as a transient rise in calcium sweeps across the egg."

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