Chien and Hu obtained cells for their most recent study from the inner membranous lining of a cow aorta. They added genetically engineered proteins tagged with red and green fluorescence markers to the bovine aortic endothelial cells, grew them in tissue culture, and filmed them while they passed fluid across the cells’ surface in a simulation of flowing blood. With that physical stimulus, paxillin consistently moved in the same direction as the fluid flow.
Paxillin is found primarily at focal adhesions, busy intersections of activity scattered around the cell’s cytoplasmic membrane. Focal adhesions are regions rich with receptors for growth factors and they are also structural attachment points that link the extracellular world to the protein filaments and tubes that comprise a cell’s internal cytoskeleton.
While researchers showed that paxillin serves as a docking station for a variety of signaling and structural proteins, they have been limited to visualizing paxillin with dyes that stain cells rigidly attached to microscope slides. Those snapshots of fixed cells can’t reveal paxillin movement.
“We can now see the dynamics of how paxillin and other proteins move inside the cell with new fluorescent labels and live-cell video microscopy,” said Chien, director of the Whitaker Institute of Biomedical Engineering at the Jacobs School.
The two-color labeling technique of Chien and Hu revealed that red-labeled paxillin is linked to green-labeled actin filaments, the thinnest of three types of protein filaments that make up the cytoskeleton of cells of higher organisms. Paxillin either slides along the actin
Source:University of California - San Diego