Directed motility of phagosomes in Tetrahymena thermophila requires actin and Myo1p, a novel unconventional myosin

Cell Motil Cytoskeleton. 2005 May;61(1):49-60. doi: 10.1002/cm.20065.


The phagosome cycle was investigated in Tetrahymena thermophila, which had internalized fluorescent latex beads. Confocal microscopy of cells from a GFP-actin strain revealed actin filaments that extended 3-5 mum from the periphery of fluorescent phagosomes. In GFP-actin cells and in wild-type cells, motility of fluorescent phagosomes was directed from the oral cavity to the posterior end of the cell. Although 60% of fluorescent phagosomes in the MYO1-knockout strain were motile, movement of phagosomes was not directed toward the posterior end of the cell and was random. Forty percent of fluorescent phagosomes in knockout cells were non-motile in contrast to only 20% non-motile phagosomes in wild-type cells. The increased incidence of non-motile phagosomes in the knockout strain could reflect absence of Myo1p as a motor. Another myosin or other molecular motors could power random movement of phagosomes in the MYO1-knockout strain. In latrunculin-treated GFP-actin cells, movement of fluorescent phagosomes was random. Average velocity of random movement of fluorescent phagosomes in the knockout strain and in latrunculin-treated cells was statistically the same as the average velocity (2.0 +/- 1.9 microm/min) of phagosomes in GFP-actin cells. These findings are an indication that dynamic actin and Myo1p are required for directed motility of phagosomes.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Actins / genetics
  • Actins / metabolism*
  • Animals
  • Animals, Genetically Modified
  • Antineoplastic Agents / pharmacology
  • Bridged Bicyclo Compounds, Heterocyclic / pharmacology
  • Cell Polarity
  • Microscopy, Confocal
  • Microspheres
  • Myosin Heavy Chains / genetics
  • Myosin Heavy Chains / metabolism*
  • Nocodazole / pharmacology
  • Phagosomes / drug effects
  • Phagosomes / metabolism*
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Tetrahymena thermophila / cytology*
  • Tetrahymena thermophila / metabolism
  • Thiazoles / pharmacology
  • Thiazolidines


  • Actins
  • Antineoplastic Agents
  • Bridged Bicyclo Compounds, Heterocyclic
  • MYO1 protein, protozoan
  • Protozoan Proteins
  • Recombinant Fusion Proteins
  • Thiazoles
  • Thiazolidines
  • Myosin Heavy Chains
  • Nocodazole
  • latrunculin A