Batten Down the Actin, Here Comes the STORM

What am I looking at?

Here, we see a section of a single cell, with the actin protein labeled with a light-emitting molecule called a fluorophore that can be switched on and off. The colored network of different size lines shows actin filaments (F-actin). This image was color-coded for depth, meaning that cool colors such as blue and purple (1) are closer to the surface that the cell is adhering to while warmer colors such as green and yellow are farther away (2).  

Biology in the Background

Actin proteins assemble into thin, helical filaments that form a network throughout all eukaryotic cells. These filaments play a significant role in cell structure, movement, division, and more. This actin network is dynamic, meaning that the filaments can either grow or shrink in length to fit the structural or movement requirements of any cell.

This image was created using STORM, an innovative super-resolution microscopy technique that utilizes photo-switchable fluorophores to reconstruct very detailed images of cellular structures. Photo-switchable fluorophores are fluorescent tags that can be switched from a dark state (essentially in the “off” position) to a fluorescently active state (essentially in the “on” position). This means that researchers can control the fluorescent activity of these fluorophores by adjusting the intensity of the activating light. So, they can sparsely activate individual fluorophores and image just those fluorophores while leaving the rest dark. Each individual fluorophore appears as a blurry disc of light due to light diffraction. The image is processed to find the center of that blurry disc, which represents the position of the labeled molecule within the cell (in this case the actin molecule). This allows for ten-to-hundred fold higher resolution than that of a conventional light microscope. In each imaging cycle, only a small fraction of the fluorophores in the field of view are activated and localized. The final image is reconstructed by repeating this process numerous times to determine the positions of nearly all molecules in three dimensions.

This technique will allow researchers to study cellular structures in much greater detail. The knowledge gained could provide researchers with a better understanding of the inner workings of the cell and could lead to future research on human health and disease.

An actin filament is approximately 7 nanometers thick, or roughly 10,000 times smaller than the width of a human hair.

Technique

These images were created using super-resolution fluorescence microscopy.