Sugar-coated sea urchin eggs could have sweet implications for human...( similar in all sea urchin species. In ...)

similar in all sea urchin species. In reality, the jelly coating contains a general type of carbohydrate in the purple sea urchin but in other species the jelly becomes a secondary barrier to prevent cross-species breeding. For instance, eggs of the green sea urchin, the purple urchin's closest relative, have a different kind of carbohydrate, one that doesn't activate the purple urchin's sperm. The same holds true for purple urchin eggs and green urchin sperm. That means that just a small chemical change in a sugar molecule can limit fertilization.

The discovery, Biermann said, tells evolutionary biologists that sibling species have found different means to regulate their reproduction.

"It helps to understand the process if you think of fertilization as sperm entering through several doors," she said. "In the past, we have focused on changes in the lock to the egg's protein door, and how sperm proteins are able to unlock that door. Now we know that eggs can change the lock in the carbohydrate door too."

Biermann is first author of a paper describing the findings in the September-October edition of the journal Evolution & Development. Co-authors are Jessica Marks of the University of Bergen in Norway; and Ana-Cristina Vilela-Silva, Michelle Castro and Paulo Mouro of the Universidade Federal do Rio de Janeiro in Brazil.

While mammal eggs mouse and human, for instance don't have a thick jelly coating like sea urchin eggs, they do have complex carbohydrate molecules on the surface. It is likely, Biermann said, that those sugars attach to proteins in sperm cells to trigger reproduction.

"They are different but they probably do exactly the same thing as sea urchin eggs," she said.

She noted that proteins are much better understood than sugars, so the role of the proteins in sperm can be studied relatively easily. Figuring out exactly how the complex sugars work will take more research, but developing such understand
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Contact: Vince Stricherz
vinces@u.washington.edu
206-543-2580
University of Washington
13-Sep-2004

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