Humans have long understood the connection between sexual intercourse and birth; and in 1876 two scientists independently described the entry of sperm into the egg and their combination into a single new nucleus. However, the scientific and medical communities have been at a loss to explain the fundamental biology behind the initial interaction in humans and other animals until now. On Wednesday, the journal Nature published a study by Wellcome Trust Sanger Institute researchers at Cambridge who discovered how surface proteins enable the two gametes to recognize each other, conceive, and begin life.
From Dr. Gavin Wright, senior author of the study:
“We have solved a longstanding mystery in biology by identifying the molecules displayed on the sperm and egg which must bind each other at the moment we were conceived. Without this essential interaction, fertilization just cannot happen. We may be able to use this discovery to improve fertility treatments and develop new contraceptives.”
Japanese researchers discovered the sperm’s binding protein in 2005 and called it Izumo, after a Japanese marriage shrine. The Sanger Institute team created an artificial version of mouse Izumo, then used it to identify its single binding partner on the surface of the mouse egg. They called the new protein “Juno” for the Roman Goddess of fertility and marriage, equivalent to Hera in Greek mythology. Watch the video about the experiment here.
The team is now testing infertile women for defects in the Juno receptor that might cause infertility. If they find a link, health providers may be able to screen for the Juno protein easily and thus reduce the expense and uncertainty of the usual assisted fertility treatments.
Erika Check Hayden’s report in Nature explains the implications for contraception technology:
“The discovery also points to potential ways to block the fusion of sperm and egg to prevent pregnancy. Scientists could now study the structure of the Juno–Izumo1 complex, and perhaps develop a new class of contraceptive drugs that interfere with this junction.”
If one protein or the other could be inactivated, the contraception arguments about whether or not fertilization has taken place and whether the blastocyst has attached to the uterine wall would become moot. The Juno-Izumo attraction occurs before both of these events, which have each been claimed to constitute the beginning of life. Preventing the protein interaction would effectively guarantee against any possibility of zygote formation. In other words, there would be zero possibility of abortion or “termination” involved in the process. Abortion is not possible before there is life.