Identification of a novel actin-related protein in Tetrahymena cilia

Cell Motil Cytoskeleton. 2006 Jul;63(7):437-46. doi: 10.1002/cm.20136.


Actin is an ancient cytoskeletal protein that plays many essential roles in cell motility. In eukaryotes, its gene belongs to a highly conserved gene family, while the protein is also a member of an actin superfamily comprising various kinds of actin-related proteins (Arps). A ciliate, Tetrahymena, has a unique conventional actin. Data from the TIGR Tetrahymena genome project and our own research suggest the existence of 12 actin-like sequences: four conventional actins, two of Arp4, one each of Arp1, Arp2, Arp3, Arp5, and Arp6, and a novel actin-related protein, tArp. We cloned the entire cDNA sequences of Tetrahymena Arp2 (tArp2), Tetrahymena Arp3 (tArp3), and tArp for the work described herein. In phylogenetic analyses, tArp was not included in any Arp subfamily. Unlike other known Arps, tArp localizes in cilia, and its expression was upregulated after deciliation. To see the precise localization of tArp, cilia were fractionated and analyzed using specific antibodies. tArp was observed preferentially in the "outer-doublet" fraction, while actin was found in the "crude-dynein" fraction. In immunoelectron microscopy, most of the gold particles were found either on the outer-doublet or central-pair microtubules. These results suggest that tArp is a ciliary component and that it has a unique function in the formation and maintenance of cilia.

MeSH terms

  • Actin-Related Protein 2 / chemistry
  • Actin-Related Protein 2 / metabolism*
  • Actin-Related Protein 2 / ultrastructure
  • Actin-Related Protein 3 / chemistry
  • Actin-Related Protein 3 / metabolism*
  • Actin-Related Protein 3 / ultrastructure
  • Amino Acid Sequence
  • Animals
  • Cell Fractionation
  • Cilia / chemistry*
  • Cilia / ultrastructure
  • Cloning, Molecular
  • Conserved Sequence
  • DNA, Complementary / genetics
  • Dyneins / metabolism
  • Microscopy, Immunoelectron
  • Molecular Sequence Data
  • Phylogeny
  • Protozoan Proteins / chemistry
  • Protozoan Proteins / metabolism
  • Protozoan Proteins / ultrastructure
  • Sequence Homology, Amino Acid
  • Tetrahymena / physiology*


  • Actin-Related Protein 2
  • Actin-Related Protein 3
  • DNA, Complementary
  • Protozoan Proteins
  • Dyneins