Doing more with less: Sperm without a fully active tail move faster and more efficiently, new UK study finds

Sperm cells moving their long tail to swim through the body in search of an egg is a familiar image, but a fully 'powered' tail may not be the key to success, according to a new UK study which could be crucial for improving the outcomes of assisted fertility treatments. Propulsion of sperm and how the cell uses its tail to move through the thick fluids of the reproductive tract to reach and fertilise an egg has been well studied. However, the role of the specific parts of the tail, including the inactive area at the very tip, which it is thought, lacks the structure needed to generate motor activity, remains unclear. A multi-disciplinary team of mathematicians and scientists from the University of Birmingham used mathematical simulations to analyse the effect that this inactive region has on the overall movement of the sperm and how this contributes to the speed and efficiency of the cell's motility. The study is the first modelling simulation study to investigate the detailed effects of this area, which measures just 3 microns - or 25 times smaller than the width of a human hair. Results showed that instead of hindering the cell, the inactive region at the end of the tail actually enables faster and more efficient swimming. Simulations showed as much as a 430% increase in efficiency and a 70% increase in velocity in sperm cells with an inactive end region of the tail compared with cells where the tail was fully active.