Despite the importance of the sperm-egg interaction, "we don't know at the molecular level how this works in any organism," said Greenstein, Ph.D., associate professor of Cell & Developmental Biology at Vanderbilt University Medical Center. Greenstein and colleagues have now identified a sperm-sensing receptor in the eggs of a microscopic worm. Their work, reported Jan. 15 in Genes & Development, is the first to find a receptor that participates in egg maturation and ovulation.
The current work is actually the second chapter of a story that started several years ago when Michael A. Miller, Ph.D., a postdoctoral fellow in Greenstein's laboratory, began searching for the signal that lets worm eggs know it's time to mature and be ovulated.
In most animals, including worms and human beings, eggs are arrested in an immature state until they receive a signal to reenter the cell cycle and mature. In human beings, the trigger for this egg maturation process is unknown. In worms, it is a signaling protein released by sperm. Miller and Greenstein identified the worm maturation signal as MSP (major sperm protein) and reported their findings in Science in 2001. And now they've found the receptor and signaling pathway that MSP uses to promote egg maturation and ovulation.
Greenstein hopes their research will shed light on problems with egg maturation in human beings. Conservative estimates suggest that about five percent of human pregnancies result in embryos with an extra chromosome, he said, most likely due to failures in egg maturation -- specifically, failures in a cell division process called meiosis. These pregnancies usually end in miscarriage.
"Human beings are really bad at meiosis," Greenstein said. "We hope that by studying
Contact: Leigh MacMillan
Vanderbilt University Medical Center