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Fruit fly egg cells create miniature tornadoes in order to properly develop and function, and these tornadoes could be widespread in large cells of other species.

The cells that make up all living things contain a fluid called the cytoplasm, which moves around in a process called cytoplasmic streaming. Although this internal movement was first observed more than a century ago, the full pattern and purpose of such fluid flows remain only partially understood.

at Princeton University and his colleagues observed the cytoplasm in fruit fly (Drosophila melanogaster) egg cells, or oocytes, using a microscope. These oocytes are roughly spherical and about 0.5 millimetres in diameter 鈥� which is much larger than most cells. The researchers found twister-like flows in the cytoplasm that caused it to slowly circle around the cell over several minutes.

Shvartsman and his team suspected that these twisters might be coming from protein assemblies called microtubules, which help give cells structure and shape. Thousands of these microtubules are attached to the cell membrane, and tiny motor proteins climb along them to move cellular cargo.

The team used simulations to calculate the effect these microtubules and motor proteins might have on the cell鈥檚 fluid and vice versa, finding that they could closely reproduce the patterns they found when observing the cells using microscopes.

鈥淭he motor is working on the microtubule: it鈥檚 carrying cargo and, as a consequence, it鈥檚 stirring the fluid,鈥� says Shvartsman. 鈥淣ow the fluid can influence the buckling of the microtubules, and all of these together can lead to self-organisation of a flow that spans the cell. This is absolutely remarkable.鈥�

To properly grow and divide, oocytes need to have a stage where they distribute and mix different cellular ingredients together before fixing certain elements in place. These twisters seem to be an essential part of this early mixing stage, says Shvartsman, and they could occur in other animal egg cells that are sufficiently large.

Human egg cells are about a fifth as large as fruit fly egg cells and are probably too small for this effect to take place, but many insects, fish and amphibians have larger egg cells where these flows may be important, he says.

鈥淚t鈥檚 super interesting from the perspective of how life works,鈥� says at the University of Warwick, UK. 鈥淭he interesting thing is how little, nanoscale autonomous walking machines which are doing this [cargo] transport generate these very large-scale, organised structures inside the cell. That鈥檚 the mind-boggling thing.鈥� However, it鈥檚 important to note that the rotations are happening much more slowly than a real tornado, he says.