Their finding, published in the current issue of Developmental Cell, solves a century-old biology riddle. In most animals, such as sea urchins, fish, mice and humans, only one sperm fertilizes an egg. If multiple sperm fuse with the egg, a process known as polyspermy, the embryo will die. So the fertilized egg quickly creates protective barriers. Scientists have known for more than 30 years that, in sea urchins, hydrogen peroxide is a key player in this process. Until now, they did not know how that potentially toxic substance was produced or controlled.
Julian Wong, a Brown research associate and lead researcher on the project, set out to find the gene responsible for pumping out this peroxide. In the Sea Urchin Genome Project database, Wong found a gene that he suspected was key for this process because it looked similar to one that produces peroxide in the human thyroid.
After a series of experiments using sea urchins, Wong found that his guess was correct. While the egg matures, this gene is turned on and creates an enzyme known as urchin dual oxidase, or Udx1. Immediately after fertilization, Udx1 is activated to produce peroxide. The peroxide is then used to "stitch" together proteins on a thin layer surrounding the egg, hardening it into a tough coating. The process is complete about five minutes after fertilization.
Wong showed this essential role by obstructing the function of Udx1. When its activity was blocked, the protective barrier didn't harden, leaving the embryo vulnerable.
The authors were surprised by the results. "The best model we had was in white blood cells, which use a similar burst of hydrogen peroxide to
Contact: Wendy Lawton