Figure 1: A fluorescence micrograph of a cell showing the actin cytoskeleton (stained blue). Two RIKEN researchers have demonstrated a way to create actin networks artificially using a laser. © JOE MCKELLAR/SCIENCE PHOTO LIBRARY
A laser-based system that can create mesh-like structures in a dish that resemble the cytoskeletons of cells has been developed by two RIKEN researchers1. They demonstrated its usefulness for research by exploring how two proteins interacted with artificial cytoskeletons.
Cytoskeletons in cells are made from a dense meshwork of actin fibers. Actin cytoskeletons are vital for cells since they impart shape to cells and enable them to move, divide and generate mechanical force.
"The actin cytoskeleton is a kind of scaffold that stabilizes a cell," says Makito Miyazaki of the RIKEN Center for Integrative Medical Sciences (IMS). "It also regulates cell division, motility and various developmental processes."
Given the importance of the actin cytoskeleton, scientists have been keen to discover more about it. In particular, they want to find out how it interacts with various proteins that bind to it. But it is difficult to study the actin cytoskeleton in cells because of its thinness and complexity.
To overcome this problem, researchers have been devising ways to create actin networks in dishes. But it is challenging to control the construction of actin networks in space and time using current methods. It is also hard to vary the network density.
Now, Miyazaki and Kei Yamamoto, also of IMS, have overcome these shortcomings by developing a new method that effectively acts as a 3D laser printer, constructing actin networks in three dimensions.
The pair co-opted a light-based technique that is often used in neuroscience to excite neurons in the brain-optogenetics-to induce molecules of actin to bond together.
By varying the power, pulse length and pattern of the light beam, they could control the density, thickness and shape of the resulting actin network.
Inside cells, the construction of actin networks depends on the interaction of multiple signaling pathways, making it hard to analyze.
"We've established a method that can manipulate a single parameter of the actin network independently of the signaling pathways," says Miyazaki. "As far as we're aware, it's the first tool to be able to do this."
In a demonstration of the technique's power, Miyazaki and Yamamoto used it to explore how the density of the actin network affected two common actin-binding proteins: myosin, which enables the actin cytoskeleton to generate force, and cofilin, which degrades actin filaments.
In the case of myosin, they found that just a small increase in network density prevented the protein from infiltrating the network. In contrast, cofilin could enter the network irrespective of its density.
The pair intend to use their method to discover how the actin cytoskeleton controls cell division and the direction of cell motility.
