When you’re trying to get pregnant, after a while, cuddling afterwards will inevitably be replaced by the charming beetle pose – lying on your back, legs up in the air. All in the hope of getting the little swimmers on their way to their goal. On their journey through the cervix, uterus and the oviduct they cover a route thousand times longer than the length of a sperm cell. Also, while sperm might travel along in a current of fluid in the cervix and uterus, in the oviduct mucus flows in the opposite direction to the sperms itinerary. How sperm manages to stay on track and not stray is not known, but understanding this process would help in improving the odds of fertilization, both during natural conception and IV treatment.
Researchers from the University of Cambridge now show that human sperm swims similar to a fish swarm with their head facing the current. This rheotaxis allows fish swarms to adapt to counter flows. Using microfluidic devices, in which liquid is forced to flow through tiny channels, the researchers show that human sperm cells not just align against the counter flow, but move along the walls of the channels. The sperm cells end up spiralling along the edges of the oviduct. This increases the chance of meeting a potential egg and could so help the sperm cells find the egg. The researchers suggest that this could help in the design of artificial insemination, by for example optimizing the fluid used for fertilisation. Whether we can replace the beetle pose with something a tad more dignified is not known – yet.
Original paper in eLife: Rheotaxis facilitates upstream navigation of mammalian sperm cells – http://elifesciences.org/content/3/e02403