Cell tracking: turning human sperm form heart-shaped trajectories. [Warwick University]

In a move that could improve IVF and fertility treatments, UK-based researchers have used 3D motion analysis to determine exactly how sperm moves.

While all sperm tails - flagella - rotate counter-clockwise to enable the cells to move through fluid, this counter-clockwise motion suggests that sperm should only be able to turn left.

However as part of their sperm locomotion studies, Dr Vasily Kantsler from the Department of Physics at the University of Warwick , and colleagues, observed that some 50% of sperm moved to the right.

As Kantsler points out: "Successful sperm navigation is essential for sexual reproduction, yet we understand relatively little about how sperm cells are able to adapt their swimming motion in response to chemical and physical cues."

With this in mind, the researchers first used single cell tracking to follow sperm in microfluidic chambers, identifying two distinct swimming states.

Heart shaped trajectories suggested the sperm could turn right or left against fluid flow, prompting the researchers to found out why.

They went onto develop a novel algorithm to reconstruct the 3D flagella beat patterns of the human sperm cells that would cause these different left and right turning movements.

And contrary to current belief, analysis indicated the cell's turning direction is not due to its rolling direction, but rather buckling at its centre.

3D reconstruction of sperm flagella motion. Grayscale image can be processed to identify out-of-plane coordinate of the flagella.

"Our analysis reveals that the swimming strokes of human sperm are considerably more complex than previously thought, and that a sperm may use its head as a rudder to turn right or left," says Kantsler.