The search for the mechanisms underlying synchronisation can yield insights on many fronts
- Raymond Goldstein
Many different types of cell, including sperm, bacteria and algae, propel themselves using whip-like appendages known as flagella. These protrusions, about one-hundredth of a millimetre long, function like tiny oars, helping cells move through fluid. Similar, shorter structures called cilia are found on the surfaces of many cells, where they perform roles such as moving liquids over the cell.
Flagella and cilia are remarkably versatile: they transport mucus and expel pathogens from our airways, they establish the left-right asymmetry in developing vertebrate embryos, and transport human eggs through the Fallopian tube. Each cilium or flagellum beats to its own characteristic rhythm, but wherever large groups of these biological paddles are found, they tend to row in sync, as though led by a cox.
Exactly what causes these microscopic rowers to move together is something of a mystery. Experiments in the 1940s demonstrated that the flagella of bull sperm tend to synchronise when they swim close to one another, connected only through the fluid surrounding them. However, the precise mechanism through which groups of cilia and flagella lock into sync with one another is not entirely clear.
A long-standing hypothesis is that movement of the fluid due to the beating flagella could be the reason they move in unison. While previous experimental findings were consistent with mathematical theories describing the fluid motion, these experiments could not exclude other mechanisms for achieving synchronisation, such as chemical signalling or physical connections between flagella.
Now, using a newly devised experimental procedure, researchers from the University of Cambridge have been able to disentangle the various mechanisms, and show that the fluid motion created by two beating flagella is sufficient by itself to cause them to row in sync. The findings are published this week in the journal eLife.
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Image: Overlaid waveforms of the flagellar beating of two somatic cells of Volvox carteri held on separate glass micropipettes.
Credit: D.R. Brumley, K.Y. Wan, M. Polin, and R.E. Goldstein
Reproduced courtesy of the University of Cambridge
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