The study focused on understanding what some sperm may gain as a competitive advantage over the millions of others competing for the same prize. Sperm face a challenging task as they swim against the current in a fluid similar to corn syrup. This is the challenge mammalian sperm encounter as they race to reach the egg. Reza Nasrallah, a mechanical engineer at Monash University in Melbourne, Australia, states that sperm are not affected by the current nor do they avoid it. In fact, Reza and his team discovered that the need to navigate the female reproductive tract helps sperm swim with optimal efficiency and may guide them to their desired destination. The findings are published in the journal Cell Reports Physical Science.
Challenges in the Female Reproductive Tract
As sperm swim against the current, they pass through secretions that vary in thickness and flow rate. One of the first obstacles comes at the cervix, the gateway to the uterus. There, a very strong flow exists due to mucus secretions from cells within the cervix. This current helps flush out any harmful bacteria that cause diseases, which are not known as strong swimmers. It acts as a barrier and filter to maintain a favorable environment for fertilization. Once sperm reach the fallopian tubes, where fertilization usually occurs, they encounter more viscous fluids and a meandering path leading to dead ends…
The Effect of Viscosity on Sperm Behavior
However, these changes may not hinder the swimmers’ progress but could instead provide cues or indicators that give smarter cells an advantage. Could this be a mechanism that allows higher-quality sperm or smarter cells to adjust their swimming behavior to gain some competitive edge over the millions of other sperm swimming in the reproductive tract? To find the answer to this question, Reza and his team put revolutionary sperm to the test.
The Effect of Viscosity on Sperm Behavior
They used revolutionary sperm because they are very similar to human sperm in terms of shape and mobility. But they did not want to look at sperm in large quantities. They aimed to study these behaviors at the single-cell level, meaning they looked at the same cell while varying the flow and changing the viscosity.
Building a Sperm-Sized Testing Arena
The researchers built a sperm-sized testing arena, or rather, a microfluidic channel. Each microfluidic channel has three different inlets for varying viscosities so they can expose sperm to different viscosities, and they also have different flow rates to simulate the state of fluid in the female reproductive tract. To ensure that the sperm did not swim out of the microscopic field of view, they tethered their heads to the floor of the chamber, which was also essential for monitoring things once the tap was opened.
The Effect of Viscosity on Sperm Behavior
After all these setups, what did they find? What they observed is that viscosity plays a more significant role than shear rate in influencing the shape of the sperm’s flagellum and sperm behavior overall. When sperm swim in a more viscous fluid, they reduce the strength of their flagellar beats and then move with a smaller wave. Those cells that can exhibit this type of behavior swim in a more energy-efficient manner. This behavior may give them a biological boost. Perhaps another cell is trying much harder. But it is not doing so in the right way, and it cannot push forward. Thus, the sperm that can shift gears and move easily…
Applications of the Study
Reza notes that the findings could contribute to developing fertility treatments in which the doctor selects the sperm that will be presented to the egg. Perhaps when it comes to treatment strategies, we need to move towards more viscous media that resemble the properties of fluids in a living organism, as this may lead to selecting better cells and a strategy based on natural swimming behavior. In other words, making sperm work for it. I believe that if you have a sample with relatively active cells, making the race more difficult increases your chances of getting the best cells.
Conclusions
Study
Although the sticky challenge may lead to better outcomes for treatments such as in vitro fertilization, studies on animals must be conducted to confirm the hypotheses we propose. While waiting for those results, Reza and Farin will continue to discuss their work, or at least attempt to do so. Reza says, “It’s a little strange to start a conversation about sperm and such things.” Reza adds, “I think it’s a start; it’s always difficult to talk about it…” Farin responds, “Yes.” Reza continues, “But once you start, especially at parties or something like that, people will follow along. And they will remember it.”
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Source: Scientific American
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