Mouse Study Reveals New Secrets of Fertilization
British researchers discover receptors on egg cells that allow sperm to attach, fertilize egg
Wright and his team built on the Japanese Izumo1 research, creating an artificial version of the Izumo protein and using it to identify binding partners on the surface of mice eggs. Using this method, they learned that Izumo1 on the sperm paired with Juno on the egg to induce fertilization.
The researchers also developed mice that lacked the Juno protein on their egg surface, finding these mice to be infertile and incapable of fusing with normal sperm. Similarly, male mice lacking the Izumo sperm protein are also infertile, highlighting the vital roles of the receptors to fertility.
An interesting feature of the Juno egg receptor, Wright said, is that it disappears within about 40 minutes after an egg is fertilized.
"We believe this is one of the ways in which eggs ensure that they fuse with one and only one sperm," he said. "That is, once the first sperm has fertilized the egg, the egg shuts down its ability to recognize additional sperm, ensuring that the fertilized egg doesn't contain too many chromosomes, which would result in a non-viable embryo."
Dr. Michael Heard, a reproductive endocrinologist at Houston Methodist Hospital in Texas, lauded the new research as "very interesting" and said the findings hold promise for future fertility treatments and contraceptives.
"A male contraceptive is still on the back burner. If they could inhibit those [Izumo1 sperm] receptors so they wouldn't fertilize the eggs at all, with a high percentage of reliability, that would be great," said Heard, who wasn't involved in the study.
Scientists note that research involving animals often fails to provide similar results in humans.