How to Stop a Sperm Cell (Or Make It Go Faster)

Multiple sperm cells surrounding egg cell prior to fertilization.

Image Courtesy of TBIT

Male birth control. Oh, how much easier life would be if it existed! It may seem like women will forever be plagued with the maddening task of popping a pill once daily to greatly decrease their chances of becoming pregnant. However, researchers at the Yale School of Medicine are currently looking into the molecular mechanisms that enhance or inhibit sperm motility, and how those mechanisms can be altered to possibly create a method of birth control for men. 

I had the pleasure of interviewing Jae Yeon Hwang, associate research scientist from Dr. Jean-Ju Chung’s lab at the Yale School of Medicine, who is currently carrying out research regarding male germ cells. Understanding the complex nature of his work, I thought it best to ask how he might explain the research he is doing with sperm cells to someone who may not be familiar with the science of sperm motility and developmental biology. “In a birth process, the major two factors which can achieve new life are the sperm and egg,” he said. “After sperm cells are inseminated into the female reproductive tract, they simply migrate to meet the egg and penetrate it.”

However, there is more to the story. After insemination into the female reproductive tract, sperm cells begin their journey to the egg and are met with diverse female reproductive tract environmental factors. During this journey, sperm cells obtain fertilizing abilities – abilities referred to as capacitation – and this biological process triggers sperm cells to develop a unique motility pattern called hyperactivated motility characterized by high amplitude flagellar beating. “Hyperactivated motility is triggered by an calcium influx,” Hwang said. 

While researchers knew that calcium was essential for the development of hyperactivated motility, they did not know how, specifically, the CatSper channel arranged itself on the sperm tail. It was the work of this lab that built upon knowledge of the previously discovered CatSper channel to understand how exactly the CatSper channel is arranged on the sperm tail. When functional, CatSper allows for the crucial calcium influx into sperm cells that results in hyperactivated motility. However, if the CatSper channel is deficient, calcium cannot enter sperm cells and this cannot trigger hyperactivated motility, resulting in male infertility. 

Hwang’s work comes into play because the goal of his study was to understand how the CatSper channel is linearly arranged along the sperm tail. “[CatSperτ, a protein found on the cell membrane of sperm cells encoded by the C2cd6 gene] is recruited to the base of the elongating sperm tail and expected to be fused into the plasma membrane and transported to the sperm tail,” he said. Without CatSperτ, Hwang found that the linear arrangement of the CatSper channel fails to occur, thus impairing sperm hyperactivated motility and resulting in male infertility.

And with the accomplishment of valuable research comes great moments of pride. I wanted to know one thing about Hwang’s research that made him proud. He responded by saying that while the acceptance from the journal, Cell Reports, to publish his work was enough to make him incredibly proud, what made him even happier was reading the peer reviewers’ comments on his paper describing how much they enjoyed reading his study. Realizing other experts in his field valued the work he was doing, Hwang felt a sense of pure fulfillment.

After hearing about the various accomplishments involving Hwang’s research, I wanted to understand the implications of his challenging but important work. Hwang said a new method of male contraception is theoretically possible if they can block the CatSper channel and associated proteins. Conversely, he said if someone is having problems with fertility, the problem can be approached using knowledge of the CatSperτ-CatSper relationship. 

Looking towards the future, it is clear that, with the help of the scientific progress made by Hwang and his colleagues, we are on the brink of tremendous possibilities regarding male germ cells.