Biology Forums - Study Force

In a sexual life cycle, fertilization represents the fusion of gametes, combining two haploid genomes (from the maternal and paternal parents) to form a diploid zygote. In order to maintain the correct number of chromosomes in the diploid generation, it is essential that only a single sperm fuse with each egg. Polyspermy, the fusion of two or more sperm with a single egg, results in an incorrect number of chromosomes in the zygote and is almost always lethal.

In animals, polyspermy is prevented by a number of mechanisms. Using fertilization of sea urchin eggs as a model for vertebrate and mammalian systems, Rick Steinhardt, Gerald Shatten, and their colleagues examined the role that changes in cytoplasmic Ca2+ concentration play in preventing polyspermy.

Part A - Experimental technique: Tracking cytoplasmic Ca2+ distribution after a sperm enters the egg
Based on what they knew about the fertilization envelope (a protective layer that forms around the egg when a sperm fuses with it), Steinhardt, Shatten, and their colleagues hypothesized that changes in the distribution of Ca2+ ions in sea urchin eggs are involved in the formation of the fertilization envelope.
In sea urchin eggs (as in most eukaryotic cells) the concentration of Ca2+ ions is much higher in the endoplasmic reticulum (ER) than in the cytoplasm. To see how cytoplasmic Ca2+ concentration changes in the egg during fertilization, the researchers injected a Ca2+-specific fluorescent dye into the cytoplasm of unfertilized eggs. After adding sperm to the eggs, they observed the eggs with a fluorescence microscope.
The following images show the changes in fluorescence that occurred after a single sperm entered the egg. The fluorescence of the dye increased with increasing cytoplasmic Ca2+ concentration. The green color indicates the region of the cell with the highest fluorescence at that point in time.

Sort the labeled regions of the fertilized egg above based on the status of the ER Ca2+ channels and Ca2+ pumps in that region.

See if this attachment helps. Look up the word 'urchin'.

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