A breakthrough that could be used to design a new class of contraceptive pills has been made by scientists.
A sperm's path to an egg is more a deadly obstacle course than a track sprint. The one ejaculated sperm cell in a million that is lucky enough to reach the fallopian tubes, where eggs await fertilization, must conquer thick, gelatinous layers of mucus and cells surrounding the egg to reach its prize.
Fortunately for the sperm, there is help. Two studies have shown how sperm sense progesterone, a female sex hormone that has been released by cells surrounding the egg. The hormone may guide the sperm towards the egg as well as giving it a final push to get there, the research suggests. The findings could be used to design a new class of contraceptive drug.
The latest studies, led by independent teams in Germany and the United States, have shown that progesterone activates a molecular channel called CatSper, which floods sperm cells with calcium.
Mice without the channel are infertile, as are some men with mutations in the genes that make it, says Polina Lishko, a reproductive biologist at the University of California, San Francisco, who led one of the studies2. Sperm that don't make CatSper cannot become hyperactive.
Lishko and Kirichok's team developed a way of measuring the electrical currents within sperm that are created by ions like calcium, similar to how neuroscientists record the electrical activity of neurons.
They found that adding progesterone to ejaculated human sperm boosts the current, and that treating sperm with drugs that block CatSper reduces it. Putting the cells into high-pH environments, like those found around the egg, also activated CatSper. A combination of high pH and high progesterone had an even stronger effect.
A second team, led by Benjamin Kaupp, a biophysicist at the Center of Advanced European Studies and Research in Bonn, Germany, came to the same conclusion in their own experiments1.
"The consequence for humans is that if you could block CatSper it would be an ideal contraceptive," the Nature quoted David Clapham, a biochemist at Children's Hospital Boston in Massachusetts, whose team discovered the channel and is looking for drugs that inhibit it, as saying.
The study has been published in Nature.