Myosin light chain kinase regulates cell polarization independently of membrane tension or Rho kinase.
Cells polarize to a single front and rear to achieve rapid actin-based motility, but the mechanisms preventing the formation of multiple fronts are unclear. We developed embryonic zebrafish keratocytes as a model system for investigating establishment of a single axis. We observed that, although keratocytes from 2 d postfertilization (dpf) embryos resembled canonical fan-shaped keratocytes, keratocytes from 4 dpf embryos often formed multiple protrusions despite unchanged membrane tension. Using genomic, genetic, and pharmacological approaches, we determined that the multiple-protrusion phenotype was primarily due to increased myosin light chain kinase (MLCK) expression. MLCK activity influences cell polarity by increasing myosin accumulation in lamellipodia, which locally decreases protrusion lifetime, limiting lamellipodial size and allowing for multiple protrusions to coexist within the context of membrane tension limiting protrusion globally. In contrast, Rho kinase (ROCK) regulates myosin accumulation at the cell rear and does not determine protrusion size. These results suggest a novel MLCK-specific mechanism for controlling cell polarity via regulation of myosin activity in protrusions.
Department of Chemical and Systems Biology, Department of Biochemistry, and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305.
Sunny S
SS
Lou
Department of Bioengineering and Biophysics Program, University of California, Berkeley, Berkeley, CA 94720 Department of Bioengineering and Biophysics Program, University of California, Berkeley, Berkeley, CA 94720 Cardiovascular Research Institute and Department of Biochemistry, University of California, San Francisco, San Francisco, CA 94158 Cardiovascular Research Institute and Department of Biochemistry, University of California, San Francisco, San Francisco, CA 94158.
Alba
A
Diz-Muñoz
Cardiovascular Research Institute and Department of Biochemistry, University of California, San Francisco, San Francisco, CA 94158 Cardiovascular Research Institute and Department of Biochemistry, University of California, San Francisco, San Francisco, CA 94158.
Orion D
OD
Weiner
Department of Bioengineering and Biophysics Program, University of California, Berkeley, Berkeley, CA 94720 Department of Bioengineering and Biophysics Program, University of California, Berkeley, Berkeley, CA 94720 Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Daniel A
DA
Fletcher
Department of Chemical and Systems Biology, Department of Biochemistry, and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305 Department of Chemical and Systems Biology, Department of Biochemistry, and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305 theriot@stanford.edu.
Julie A
JA
Theriot
D000818:Animals; D015153:Blotting, Western; D002448:Cell Adhesion; D002462:Cell Membrane / Q000201:enzymology / Q000473:pathology*; D002465:Cell Movement; D016764:Cell Polarity; D048430:Cell Shape; D002478:Cells, Cultured; D060527:Corneal Keratocytes / Q000166:cytology / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism*; D005434:Flow Cytometry; D009219:Myosin-Light-Chain Kinase / Q000235:genetics / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D010766:Phosphorylation; D011554:Pseudopodia / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015027:Zebrafish / Q000254:growth & development / Q000378:metabolism*; D054460:rho-Associated Kinases / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D054460:rho-Associated Kinases; D009219:Myosin-Light-Chain Kinase; D009218:Myosins