A team of researchers has added to the world’s understanding of how cells use filopodia to move around in our bodies. This discovery about how cells move has never been addressed.
“While the cell doesn’t have eyes or a sense of smell, its surface is equipped with ultra-slim filopodia that resemble entangled octopus tentacles. These filopodia help a cell move towards a bacterium, and at the same time, act as sensory feelers that identify the bacterium as a prey,” explained Poul Martin Bendix, PhD, associate professor in biophysics at the Niels Bohr Institute (NBI) at the University of Copenhagen.
The discovery is not that filopodia act as sensory devices—which was already well established—but rather about how they can rotate and behave mechanically, which helps a cell move, as when a cancer cell invades new tissue.
The work is published in Nature Communications in the paper, “Filopodia rotate and coil by actively generating twist in their actin shaft.”
The Niels Bohr Institute has unique equipment for this type of research. When an object is extraordinarily small, holding onto it mechanically becomes impossible. However, it can be held and moved using a laser beam with a wavelength carefully calibrated to the object being studied—or optical tweezers.
“At NBI, we have some of the world’s best optical tweezers for biomechanical studies. The experiments require the use of several optical tweezers and the simultaneous deployment of ultra-fine microscopy,” explained Bendix.
The cancer researchers are interested in whether switching off the production of certain proteins can inhibit the transport mechanisms which are important for the filopodia of cancer cells. According to Bendix, the mechanical function of filopodia can be compared to a rubber band. Untwisted, a rubber band has no power. But if you twist it, it contracts. This combination of twisting and contraction helps a cell move directionally and makes the filopodia very flexible.
“They’re able to bend—twist, if you will—in a way that allows them to explore the entire space around the cell, and they can even penetrate tissues in their environment,” said lead author, Natascha Leijnse, PhD, assistant professor at the NBI.
“Obviously, our results are of interest to cancer researchers. Cancer cells are noted for their being highly invasive. And, it is reasonable to believe that they are especially dependent on the efficacy of their filopodia, in terms of examining their surroundings and facilitating their spread. So, it’s conceivable that by finding ways of inhibiting the filopodia of cancer cells, cancer growth can be stalled,” explained Bendix.
The project involved interdisciplinary collaboration at the Niels Bohr Institute, where associate professor Amin Doostmohammadi, PhD, who heads a research group that simulates biologically active materials, contributed with the modeling of filopodia behavior. “It is very interesting that Amin Doostmohammadi could simulate the mechanical movements we witnessed through the microscope, completely independent of chemical and biological details,” explained Bendix.
The mechanism discovered by the Danish researchers appears to be found in all living cells. Besides cancer cells, it is also relevant to study the importance of filopodia in other types of cells, such as embryonic stem cells and brain cells, which are highly dependent on filopodia for their development.
