This approach could have a significant impact on the bovine industry in the U.S. and globally as IVF is an increasingly popular method for breeding cattle
UConn cows on Horsebarn Hill (Sydney Herdle/UConn Photo)
Up until the 1950s, scientists were scratching their heads trying to figure out why their experiments using perfectly healthy eggs and sperm to develop in-vitro fertilization (IVF) were unsuccessful.
Then, they made a critical discovery - sperm capacitation.
Maria Gracia Gervasi, assistant professor of animal science in the College of Agriculture, Health and Natural Resources, is an expert on sperm capacitation and the application of assisted reproductive technologies such as IVF in rodent and bovine species. She is part of a team that recently developed a new method for sperm capacitation that makes bovine IVF more effective.
Sperm capacitation is a set of processes mammalian sperm need to undergo while they are inside the female reproductive system before they can fertilize an egg.
During capacitation, a series of molecular pathways are activated that cause the sperm to move differently, known as "hyperactive motility." The sperm needs to be moving this way to successfully penetrate an egg to fertilize it. There are also changes to the sperm head that expose the part of the sperm that fuses with the egg during fertilization.
The discovery of capacitation enabled the development of IVF technology, revolutionizing human and animal reproduction.
Gervasi is part of a group of collaborators that published their findings in Theriogenology. Claudia E. Osycka-Salut, a researcher from the Instituto de Investigaciones Biotecnologicas (IIBio-UNSAM-CONICET), Buenos Aires is the first author on the paper.
In Gervasi's previous lab, they worked on a study showing that using a calcium ionophore - a kind of chemical that binds to and help transport ions - improved sperm capacitation in mice. This led her to wonder if it would work in bovine species as well.
When bovine sperm are capacitated in the laboratory, scientists put them in a medium containing calcium, bicarbonate, a protein called bovine serum albumin, and heparin.
"All of these components are required for sperm capacitation in bovine species and IVF," Gervasi says.
When Gervasi and her team introduced the calcium ionophore, it increased calcium levels in the medium. This caused the sperm to stop moving. Then, when the researchers washed the calcium out of the medium, the sperm started moving again with hyperactive motility - indicating they had induced capacitation.
In this study, they found that the ionophore achieved similar results as traditional IVF procedures without heparin.
However, when they then tested the ionophore with heparin, there were significant improvements in fertilization rates and embryo development.
The fertilization rate for sperm treated with the ionophore was 83%, compared to 70% in the untreated group. The rate of fertilized eggs that developed into embryos increased from 11% to 27%.
"The difference is just adding this little sperm treatment before using it for IVF," Gervasi says.
This approach could have a significant impact on the bovine industry in the U.S. and globally as IVF is an increasingly popular method for breeding cattle. This is because it is much easier to take semen from a bull with characteristics a farmer wants to introduce into a herd and ship that semen or embryos rather than having to move the bull around.
"The application of our treatment for in-vitro production to improve the capacitation and fertilization could have a huge impact on the industry because we could double the number of embryos," Gervasi says. "It's a big improvement."
This treatment could also improve fertilization and embryo development rates for cryogenically preserved semen that has already been sexed. The process of sexing the semen damages the sperm, leading to reduced fertilization rates.
"Being able to test our treatment with those sperm would also be very applicable to what industry is using nowadays," Gervasi says.
Gervasi will follow up this work by seeing if embryos produced from sperm treated with the ionophore remain more successful than those produced without the ionophore once implanted in an animal.
Gervasi is currently working on a separate sperm treatment that could be combined with the ionophore treatment to bolster the improvements demonstrated in this study. She is also interested in analyzing the genetic quality of the embryos produced using these treatments.
"My lab here at UConn is focused on understanding how sperm and sperm treatments during capacitation can influence not only fertilization, but post-fertilization events like embryo development," Gervasi says. "So, I will definitely be focusing a lot on embryo quality and what is the sperm bringing to it."
This work was supported by Agriculture and Food Research Initiative Competitive #2022-67016-36302 from the USDA National Institute of Food and Agriculture.
This work relates to CAHNR's Strategic Vision area focused on Ensuring a Vibrant and Sustainable Agricultural Industry and Food Supply.
