Egg cells are among the largest cells in the animal kingdom. If moved simply by randomly moving water molecules, proteins could take hours or even days to move from one side of a forming egg cell to the other. Fortunately, nature has developed a faster method: ponds that span cells in the egg cells of non-native animals such as mice, zebrafish and fruit flies. These vortices enable cross-cell circuits that take just a fraction of the time. But until now, scientists did not know how these vital currents were created.
Using mathematical modeling, researchers now have an answer. The gyres are the result of accumulated conduction of rodlike molecular tubes called microtubules that extend in from the cell membrane, the researchers report on January 13 in Corporate Review Letters.
“While the biological function of these streams is little understood, they circulate nutrients and other factors that organize the body’s plan and drive development,” said study co-lead author David Stein, a research scientist at the Flatiron Institute ‘s Center for Computational Biology (CCB) in New York City.
Gabriele De Canio, a researcher at Cambridge University, led the study with Stein. Their co-authors were CCB director and New York University professor Michael Shelley and Cambridge professors Eric Lauga and Raymond Goldstein.
Scientists have studied cell currents since the late 18th century, when the Italian physicist Bonaventura Corti observed the interior of cells using his microscope. He saw constantly moving filters, but scientists did not understand the devices that controlled these currents until the 20th century, when they identified the source of the movement: molecular motors that walk around. nam microtubules. These motors slow down large biological payloads such as lipids. Pulling the cargo through a cellular fluid is like dragging a beach ball through honey. As the payloads move through the stream, the liquid will also move, creating a small stream.
But sometimes these streams are not so small. In certain stages of development of a common fruit fly egg cell, scientists saw water-like currents that spanned the entire cell. In these cells, microtubules extend from the cell membrane like wheat stalks. Molecular motors direct these microtubules pushing down on the microtubule as they ascend. That downward force bends the microtubule, redirecting the resulting currents.
Previous studies have considered this depletion method but applied it in isolated microtubules. These studies predicted that the microtubules would circulate in circles, but that behavior did not correspond to observations.
In the new study, the researchers added a key feature to their model: the effect of neighboring microtubules. That addition showed that the flowing currents coming from the pay-as-you-go motors bend nearby microtubules in the same direction. With sufficient motors and sufficient density of microtubules, all the microtubules continue together like a wheat field trapped in strong winds. This circular alignment moves all flows in the same direction, creating the cell-wide vortex seen in the cells of true fruit flies.
Although grounded in reality, the new model is brought down to the essentials to reveal the conditions that are responsible for the flowing currents. The researchers are now working on versions that actually capture the physics behind the currents to better understand the role of the currents in biological processes.
###
Disclaimer: AAAS and EurekAlert! they are not responsible for the accuracy of press releases posted to EurekAlert! by sending institutions or for using any information through the EurekAlert system.