Cell and Tissue Mechanics
Fluorescence Methods

Mechanical studies on Cells and Tissues

We are studying the mechanical properties and functions of animal cells. Nonmuscle cells carry out various kinds of mechanical activities as individuals (locomotion, phagocytosis, division) and collectively in tissues (establishment of tissue tone). In these and other processes it is essential for the cell to be able to maintain its shape under imposed stresses or to change its shape to move or do work. Change or retention of cell shape is determined by systems of cytoplasmic filaments (actin microfilaments, microtubules, and intermediate filaments) which collectively are termed the cytoskeleton. Therefore at a molecular level cell mechanics resolves into studies of the structure and function of the cytoskeleton and its component proteins.

We use the cell poker (like a large, slow AFM) to observe the forces by which a cell can maintains or changes its shape. We use the tissue mechanical testing apparatus to observe the collective mechanical effects of cells cultured in collagen matrices. Using these methods we obtain information about both contractile forces generated within cells and about the viscous and elastic forces which resist deformation. Mechanical measurements provide a quantitative assay for the functions and activities of molecules such as myosin, gelsolin, or dystrophin.

Fluorescence microscopy: FPR, FCS, FIDA and
fluorescence lifetime and single molecule methods

Critical biological functions on the cellular level involve the diffusion, transport, association and reaction of molecules and particles on microscopic and mesoscopic scales. Fluorescence Correlation Spectroscopy (FCS), Fluorescence Photobleach Recovery (FPR) and Fluorescence Intensity Distribution Analysis (FIDA) are closely related techniques that probe these phenomena by the use of fluorescent labels. The labels may be attached to specific molecules, such as receptors in a cell membrane, or they may be molecules that partition preferentially in regions of a particular lipid species in a membrane. Molecules in solution are also studied by these methods.

Our laboratory manages (and is a principal user of) the department's Zeiss Confocor facility. We also have an Olympus microscope with several laser inputs, including a titanium-sapphire laser for two-photon excitation, That setup is maintained by Tom Stump of the Hall lab, who has described it on their website.