Symposium Science – understanding sperm motility

As part of my STP master’s degree, I carried out a research project into the effect of mechanotransduction (the conversion of mechanical signals into a biochemical or electrical signal) on sperm flagella.

Despite its significance, there is limited research on the fundamental understanding of sperm motility, which is essential for natural conception. My project aimed to identify whether increased flow rate of media over bound cells had a significant effect on some flagella properties. I assessed the changes in the beat frequency, the arc wavelength, the arc wavespeed and the power exerted by the flagellum.

To carry out the research, I used a custom-made perfusion chamber which allowed me to bind live sperm cells by their head to the chamber. This was done using poly-d-lysine to allow non-specific binding of the cells and free movement of the flagellum. A pump was used to alter the voltage and subsequently the flow rate of the media. Videos were captured of the same sperm cells at different flow rates to enable a comparison between the conditions.

I used a custom-made perfusion chamber which allowed me to bind live sperm cells by their head to the chamber

Videos were taken and analysed using the Flagellar Assisted Sperm Tracking (FAST) software. Statistical analysis was performed, and the results showed that was a significant impact on sperm flagella when they are exposed to a flow rate. This was consistent across the power exerted by the flagella, the arc wavespeed and the beat frequency. However, there was no statistical significance in the change of arc wavelength suggesting that the mechanotransducive response is to move faster but not change the shape of the movement.

The arc wavespeed had a statistically significant increase (P = 8.9 x 10^-5) with increasing flow rate, the beat frequency had a statistically significant increase (P = 3.9 x 10^-4) with increasing flow rate and the power exerted by the flagellum also had a statistically significant increase (P = 0.028) when exposed to increasing flow rates. These changes are indicative of a mechanotransducive response in sperm cells, however understanding the physiology of these changes requires further investigation.

There were some challenges which arose whilst carrying out the research, such as ensuring that I was able to image the same cell at every flow rate. This was difficult because the chamber had to stay completely still throughout the experiment, and the increasing flow rate could displace cells from their bound position.

Moving forward with this work, it would be interesting to assess the calcium signalling response of the cells withstanding physical stimulus. Using both fluorescent microscopy in conjunction with FAST analysis could provide real time data on the intracellular signalling pathway as a response to physical stimuli. This approach would offer a deeper understanding of how sperm cells process mechanotransducive signals and in turn regulate sperm motility. It would also be interesting to investigate the effect of flow rate in medias with varying viscosities to mimic the physiological conditions of natural conception.

View Rachels poster for more detail Rachel McKernan poster