The Science

The flagellum is an intricate biological structure, one hundredth the width of a human hair, actuated by a '9+2' ring of microtubules and dynein motors running through its core. Sperm have a challenging task to accomplish - they must traverse the maze-like interior of the female reproductive tract, migrating several thousand times their body length through viscous fluids, in search of the egg, which one must then penetrate in order to fertilise. The flagellum is responsible for this propulsion, navigation and penetration, both driving the cell forward and sensing the surrounding environment.

Sperm motility is one of the major factors underlying fertility problems, affecting around one in six couples, with male factors accounting for approximately half of all cases. The hetrogeneity of human sperm, coupled with the difficulty in tracking small, fast cells mean that specialised tools are needed for asessing male fertility. To this end we have developed FAST (Flagellar Analysis and Sperm Tracking). This free-to-use software package enables high-throughput tracking and analysis of the rapidly moving flagellum of motile cells.

FAST provides deep mechanistic insight into sperm motility

Despite the undeniable importance of flagellar motion, science and reproductive medicine have lacked the tools to measure, quantify and compare flagellar motion. FAST provides for the first time an openly-available package for the automated capture of flagellar movement from high speed imaging. By analysing large quantities of cells, in a variety of environments with or without stimulii, we can start to uncover the mechanisms behind changes in the flagellar beat.

Uncovering the secrets of motility to help inform clinical practice

Combining FAST with and mathematical models provides for the first time the ability to gain insight into experimentally intractable interactions. Knowledge of the sperm flagellar waveform provides much more than just kinematics. Using tracked beats with fluid mechanics modelling allows for analysis of the metabolic requirements of a swimming cell through calculation of the power dissipation owing to the movement of the flagellum. Further, by incorporating tracked data into numerical codes (such as the NEAREST system) we can investigate details of the sperm-generated local flow field, forces and energy dissipation due to flagellar motion in different environments.

Grant funding

The FAST package has been developed at the University of Birmingham, in the Mathematical Biology group and the Centre for human Reproductive Science. This work is funded by the EPSRC Rapid Sperm Capture Healthcare Technologies Challenge Award. J.C.K-B. is funded by a National Institute of Health Research (NIHR), and Health Education England, Senior Clinical Lectureship Grant: The role of the human sperm in healthy live birth (NIHRDH-HCS SCL-2014-05-001). This article presents independent research funded in part by the National Institute for Health Research NIHR and Health Education England. The views expressed are those of the FAST team and not necessarily those of the NHS, the NIHR or the Department of Health.

Sperm motility diagnostics is just one of the areas that our team work on. For more discussion of other areas and the issues surrounding fertility visit www.spermeggembryo.com