NOBEL PRIZE-WINNING technology has helped to reveal the process by which fertilisation occurs. Fertilisation normally happens as the oocyte is moved along the fallopian tube by cilia. This research has discovered that the fallopian tube not only provides aid to the oocyte, but also to the sperm using tiny particles. “There is communication between the sperm and the fallopian tube that helps prepare the sperm for its big push into the egg,” says Prof Patricia A. Martin-DeLeon, Professor of Biological Sciences, University of Delaware, Newark, Delaware, USA.
The fallopian tubes were found to release particles, termed ‘oviductosomes’; these are only 100 nanometres in diameter. The oviductosomes are released when particular hormones are present. Once released, they attach to the head of the sperm using integrin membrane receptors and fusion stalks.
The oviductosomes then transfer a plasma membrane, Ca2+-ATPase 4, which acts to pump out calcium. This is necessary for the sperm as toxic levels of calcium lead to a build-up of nitric oxide, which can cause DNA damage. The team used super-resolution microscopy, which won a Nobel Prize in 2014, to visualise this process. They found that within 1 hour of being introduced to sperm, the oviductosomes were attached to the sperm’s surface. The oviductosomes continued to accumulate after 2–3 hours, particularly on the sperm’s head and the midpiece of its tail.
This research has many implications for in vitro fertilisation (IVF). “We have shown that these oviductosomes are carrying critical molecules that include not only proteins, but also nucleic acids such as RNA and also lipids,” Prof DeLeon said. “That gives us hope they can be used as vehicles for improving fertility and the chances of producing healthy embryos and offspring.”
Prof DeLeon and her team are currently analysing the protein-rich contents of this cargo to discover exactly what provides the sperm with the necessary tools for its final push to penetrate the egg. “Our work may lead to the discovery of genes and gene products that cause infertility,” Prof DeLeon commented. “We may identify proteins required to improve the efficiency of IVF, and improve the outcome and health of the offspring. It is really another step in the direction of personalised medicine, since individuals carrying mutations of one of a variety of genes account for the largest group of infertile couples.”