UCLA biologists elucidate fertilization process

UCLA graduate student Jeffrey Riffell and UCLA biology professor Richard Zimmer report the first experimental test on the role of small-scale physics as it influences the interactions between sperm and egg, and the consequences for fertilization, at the annual conference of the Association for Chemoreception Sciences in Sarasota, Fla., April 10.

“The physics of fluid motion has a profound consequence on the ability of sperm to navigate and find an egg, and therefore on fertilization,” Zimmer said.

Riffell and Zimmer conducted their research on abalone, but their work applies to other species as well. While a theory has been postulated on what should happen to chemicals in the presence of small-scale turbulence, no scientist had tested the theory before.

“There is an optimum amount of fluid motion where fertilization is significantly enhanced,” said Zimmer, whose research is federally funded by the National Science Foundation.

Riffell and Zimmer have been able to simulate important aspects of fluid motion as abalone experience it in their natural habitats, and to assign under what conditions the chemical communication process is optimized, and fertilization is therefore maximized. Similar physical mechanisms operate whether in the turbulent ocean environment or within a mammalian reproductive tract, including humans, Zimmer said.

In related research, a team — consisting of Marc Spehr, a postdoctoral scholar at Ruhr University in Bochum, Germany; Hanns Hatt, a professor at Ruhr University; Gunter Gisselmann, Alexandra Poplawski and Christian Wetzel, all members of Hatt’s laboratory; and Riffell and Zimmer — reported findings that have potential implications for both increasing human fertilization and preventing pregnancies. The research team reported in the March 28 issue of the journal Science that they have isolated and identified a molecule (bourgeonal) that controls the navigation of human sperm cells, and the genes that code for that molecule, which may play a critical role in the fertilization process.

In addition, the scientists have discovered a potent inhibitor, called undecanal, that blocks the effects of bourgeonal on sperm.

“We are rapidly making strides in identifying the functional role in fertilization of remote chemical communication between sperm and eggs,” Zimmer said. “We are learning how chemical communication occurs.”