Cells attaching to the extracellular matrix spontaneously acquire front-rear polarity. This self-organization process comprises spatial activation of polarity signaling networks and the establishment of a protruding cell front and a non-protruding cell rear. Cell polarization also involves the reorganization of cell mass, notably the nucleus that is positioned at the cell rear. It remains unclear, however, how these processes are regulated. Here, using coherence-controlled holographic microscopy (CCHM) for non-invasive live-cell quantitative phase imaging (QPI), we examined the role of the focal adhesion kinase (FAK) and its interacting partner Rack1 in dry mass distribution in spreading Rat2 fibroblasts. We found that FAK-depleted cells adopt an elongated, bipolar phenotype with a high central body mass that gradually decreases toward the ends of the elongated processes. Further characterization of spreading cells showed that FAK-depleted cells are incapable of forming a stable rear; rather, they form two distally positioned protruding regions. Continuous protrusions at opposite sides results in an elongated cell shape. In contrast, Rack1-depleted cells are round and large with the cell mass sharply dropping from the nuclear area towards the basal side. We propose that FAK and Rack1 act differently yet coordinately to establish front-rear polarity in spreading cells.

• Keywords
• Rack1, cell adhesion, cell dry mass, cell spreading, coherence-controlled holographic microscopy, extracellular matrix, focal adhesion kinase, front–rear polarity, quantitative phase imaging,
• MeSH
• Cell Adhesion genetics   physiology   MeSH
• Cell Line MeSH
• Fibroblasts cytology   metabolism   MeSH
• Focal Adhesion Protein-Tyrosine Kinases genetics   metabolism   MeSH
• Rats MeSH
• Microscopy, Phase-Contrast MeSH
• Cell Movement genetics   physiology   MeSH
• Cell Polarity genetics   physiology   MeSH
• Receptors for Activated C Kinase genetics   metabolism   MeSH
• RNA Interference MeSH
• Cell Shape genetics   physiology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Focal Adhesion Protein-Tyrosine Kinases MeSH
• RACK1 protein, rat MeSH Browser
• Receptors for Activated C Kinase MeSH

• Publication type
• Editorial MeSH