Microscope Shows Sperm's Final Push to Fertilization

By Sandy Hemphill, Contributing Writer, BabyMed


Excited wiggling. Final drive into the end zone. Christmas tree decorations. Hydrogen fuel. What does this odd assortment of words have in common? They were all used to describe a remarkable discovery made by one of North America’s leading reproductive geneticists to describe what she saw under a high-powered microscope during the moment of a sperm’s final push to fertilization of an egg. No one had ever witnessed this event before but it could become instrumental in improving the success rate of in vitro fertilization (IVF).

Dr. Patricia A. Martin-DeLeon, of the University of Delaware where she is honored as the Trustees Distinguished Professor of Biological Sciences, had seen sperm wiggling excitedly before in her work with mice. Mice are often used in fertility studies because they are so close genetically to humans but their reproductive cycle is so much faster. A sperm wiggles wildly when it comes at last into contact with an egg after its epic voyage through the female reproductive tract.

The Nobel Prize-Winning Microscope

For her latest study of what happens in the moments before the wiggling begins, DeLeon used a Zeiss ELYRA PS.1, a high-powered, three-dimensional super-resolution microscope capable of magnifying individual molecules in a single cell. The microscope is such a technological breakthrough its inventors — Eric Betzig, Stefan Hell, and William E. Moerner — were awarded the 2014 Nobel Prize in Chemistry.

The End Zone, the Christmas Tree, and Hydrogen Fuel

What DeLeon saw through the modern marvel was what happens when the sperm passes through the fallopian tube, described as its final drive into the end zone. Here’s what happens:

• As sperm passes through the fallopian tube, tiny hair-like structures (cilia) sweep the sperm forward toward the egg.
• As each cilia sweeps the sperm, it releases oviductosomes that attach themselves to the sperm’s head and tail midsection, a sight that resembles decorations on a Christmas tree.
• Once attached, the oviductosomes wait for the perfect moment to pump out toxic calcium build-up from inside the sperm and replace it with hydrogen that will fuel the sperm for its final push toward the egg.

And then the wiggly happy dance begins.

Oviductosomes — Medical Discovery

All bodily fluids contain exosomes (tiny sacs) that are important for cellular survival. Until DeLeon’s research revealed them, exosomes in the fallopian tubes were unknown. She named them oviductosomes for oviduct (fallopian tube) and exosome. Oviductosomes measure approximately 100 nanometers (10 millionths of an inch) in diameter.

DeLeon says, “This calcium pump is required by the sperm just prior to fertilization, as well as in the early embryo. The sperm pumps out calcium and takes in hydrogen ions, which seems to give it that last push into the egg, and also is critical to starting the zygote’s life.”

DeLeon speculates this glimpse into the cargo-transport system that goes from oviductosome to sperm could someday improve the current 32% IVF success rate. “We’ve shown that these oviductosomes are carrying critical molecules that include not only proteins, but also nucleic acids such as RNA and also lipids,” she says. Her research team is currently in the process of analyzing this protein-rich oviductosome cargo to gain a better understanding of its role in sperm health, fertilization, and embryo development.


Sources:

1. Bryant, Tracey. "Reproductive assist: UD finding sheds light on infertility puzzle, could improve in vitro fertilization." UDaily. University of Delaware, 17 Sept. 2015. Web. 1 Oct. 2015.
2. Lindemann, Charles B. "Dr. Lindemann's Fun Sperm Facts!" Oakland University. Oakland University, 2011. Web. 1 Oct. 2015.