Studying the Cytoskeleton

Atomic force microscopy (AFM) determines the mechanical properties of cytoskeletal filaments by using nanosized tips to pull both ends of filaments and measure their tensile strength. This technique reveals how much force filaments can withstand before breaking, providing insight into their structural resilience and functional capabilities in cells.

Intermediate filaments are more extendible than other cytoskeletal filaments, stretching up to three and a half times their standard length before breaking. This exceptional flexibility, measured using atomic force microscopy, suggests intermediate filaments provide unique mechanical properties that allow cells to withstand significant deformation and stress.

Fluorescence microscopy visualizes kinesin motor proteins by labeling them with GFP (green fluorescent protein) and marking microtubules with fluorescent dyes. This approach allows researchers to observe kinesin proteins walking along microtubules in real-time, revealing how motor proteins interact with and move along cytoskeletal structures.

To visualize actin polymerization, purified G-actin monomers are labeled with fluorescent dye and microinjected into a live cell. The labeled subunits polymerize into actin filaments, and fluorescence microscopy detects and localizes these filaments within the cell, enabling researchers to study actin assembly dynamics in real-time.

Electron microscopy produces only static images and cannot capture the dynamic behavior of cytoskeletal filaments and their functions. Although electron microscopy provides high-resolution structural information, sample preparation procedures involving chemical fixation, dehydration, and staining preserve only a single moment in time, making it unsuitable for studying living cellular processes.

Live-cell imaging using fluorescence microscopy allows researchers to analyze molecular processes of living cells in real-time. By synthesizing fluorescently labeled proteins as GFP fusion proteins or injecting purified cytoskeletal subunits tagged with fluorescent dyes, scientists can observe the dynamic behavior and interactions of cytoskeletal structures without disrupting cellular function.

Rotary shadowing, also called metal replica, fixes cytoskeletal filaments using chemicals like glutaraldehyde or formaldehyde, then dehydrates samples using alcohol to critical point drying. Samples are embedded in resin, thin-sectioned, and stained with heavy metal salts such as platinum before electron microscopy observation, enabling high-resolution structural visualization.