George Witman, Ph.D.

Academic Role: Professor

Faculty Appointment(s) In:
   Cell Biology

Other Affiliation(s):
   Cell Dynamics Group
   Interdisciplinary Graduate Program

Cilia and Flagella, Molecular Motors, Sensory Transduction, Proteomics, Molecular Basis for Diseases Involving Cilia and Flagella

Our research is concerned with the cell biology of cilia and flagella, including the non-motile primary cilia present on most cells in our body and believed to be “cell antennae” involved in sensory reception and transduction. Our findings have important implications for male infertility, and for diseases of the lung, kidney and eye, all of which contain cilia.

In many of these studies we are using the unicellular Chlamydomonas, a model flagellated organism amenable to biochemical, genetic and molecular genetic approaches.   One area of research involves the outer dynein arm of the flagellar axoneme (Fig. 1), which is the best characterized of all dyneins and serves as the paradigm for this large class of molecular motors.   This research includes 1) characterization of a newly discovered complex that is necessary for the outer dynein arm to bind to the flagellar microtubules, and 2) study of several still uncharacterized genes known to be necessary for outer arm assembly.  The human homologues of these genes are candidates for causing primary ciliary dyskinesia, a human disease in which the outer dynein arms are frequently missing.

We also are studying a process, called “intraflagellar transport” (IFT), which involves the active movement of multi-subunit protein particles from the base to the tip of the cilium or flagellum, and back to the base again (Fig. 2).  These particles carry cargo necessary for assembly and maintenance of the cilium or flagellum, and also may be transporting signals from the cilium or flagellum to the cell body and vice versa.  We are characterizing both the motors responsible for this transport, and the individual polypeptides that make up the IFT particles.  Because IFT is essential for the assembly of all cilia and flagella, disruption of IFT-particle protein genes blocks assembly of cilia, providing a powerful tool for studying the function of primary cilia in the kidney, eye, and elsewhere.

Finally, we have recently completed a proteomic analysis of the Chlamydomonas flagellum.  This has resulted in a virtual “gold mine” of data that will form the basis for many exciting projects.  Because the proteins of cilia and flagella have been highly conserved throughout evolution, the human homologues of most of these proteins are readily identified.  This opens the door to understanding the functions of many previously uncharacterized proteins.  We currently are investigating the functions of some of the most interesting proteins using reverse genetics approaches in Chlamydomonas.  Defects in some of the homologues are known to cause disease in mice and humans, suggesting that these diseases are due to defects in cilia.

Figure 1. Diagram of two outer arm dyneins on an outer doublet microtubule.   The a, b, and g dynein heavy chains are indicated.  Numbers indicate masses of dynein intermediate and light chains.

Figure 2:  Diagram illustrating the movement of IFT particles in a flagellum.  The molecular motor kinesin II moves the particles to the tip; cytoplasmic dynein 1b returns the particles to the base.

Recent Publications

Wirschell, M., C. Yang, P. Yang, L. Fox, H. Yanagisawa, R. Kamiya, G. B. Witman, M. Porter, and W. S. Sale. 2009. IC97 is a novel intermediate chain of I1 dynein that interacts with tubulin and regulates interdoublet sliding. Mol. Biol. Cell 20: 3044-3054.

Lechtreck, K-F., Luro, S., Awata, J., and Witman, G. B. 2009. HA-tagging of putative flagellar proteins in Chlamydomonas reinhardtii identifies a novel protein of intraflagellar transport complex B. Cell Motil. Cytoskeleton. 66: 469-482.

Pazour, G. J. and G. B. Witman. 2008. The Chlamydomonas flagellum as a model for human ciliary disease. In: The Chlamydomonas Sourcebook. Vol. 3. Cell Motility and Behavior (ed. G. B. Witman). Elsevier, New York, NY. pp. 445-478.

Witman, G. B. 2008. The Chlamydomonas Sourcebook. Vol. 3. Cell Motility and Behavior. Elsevier, New York, NY. 501 pp.

Lechtreck, K-F., P. Delmotte, M. L. Robinson, M.J. Sanderson and G. B. Witman. 2008. Mutations in Hydin impair ciliary motility in mice. J. Cell Biol. 180: 633-643.

Huang, K., Diener, D. R., Mitchell, A., Pazour, G. J., Witman, G. B., and Rosenbaum, J. L. 2007. Function and dynamics of PKD2 in Chlamydomonas reinhardtii flagella. J. Cell Biol. 179: 501-514.

Merchant, S. S., S. E. Prochnik, O. Vallon, E. H. Harris, S. J. Karpowicz, G. B. Witman et al. 2007. The Chlamydomonas genome reveals the evolution of key animal and plant functions. Science 318: 245-251.

Hou, Y., H. Qin, J. A. Follit, G. J. Pazour, J. L. Rosenbaum, and G. B. Witman. 2007. Functional analysis of an individual IFT protein: IFT46 is required for transport of outer dynein arms into flagella. J. Cell Biol. 176: 653-665.

Lechtreck, K.-F. and G. B. Witman. 2007. Chlamydomonas hydin is a central pair protein required for flagellar motility. J. Cell Biol. 176: 473-482.

Yang, P., D. R. Diener, C. Yang, T. Kohno, G. J. Pazour, J. M. Dienes, N. Agrin, S. M. King, W. S. Sale, R. Kamiya, J. L. Rosenbaum, and G. B. Witman. 2006. Radial spoke proteins of Chlamydomonas flagella. J. Cell Sci. 119: 1165-1174.

Pazour, G. J., N. Agrin, B. L. Walker, and G. B. Witman. 2006. Identification of predicted human outer dynein arm genes: candidates for primary ciliary dyskinesia genes. J. Med. Genet. 43: 62-73.

DiBella, L. M., O. Gorbatyuk, M. Sakato, K. Wakabayashi, R. S. Patel-King, G. J. Pazour, G. B. Witman, and S. M. King. 2005. Differential light chain assembly influences outer arm dynein motor function. Mol. Biol. Cell 16: 5661-5674.

Pazour, G. J., N. Agrin, J. Leszyk, and G. B. Witman.  2005.  Proteomic analysis of a eukaryotic cilium.  J. Cell Biol. 170:  103-113.

Hou Y, G. J. Pazour, and G. B Witman.  2004.  A dynein light intermediate chain, D1bLIC, is required for retrograde intraflagellar transport (IFT). Mol. Biol. Cell 15:  4382-4394.

Wirschell, M., G. Pazour, A. Yoda, M. Hirono, R. Kamiya, and G. B. Witman.  2004.  Oda5p, a novel axonemal protein required for assembly of the outer dynein arm and an associated adenylate kinase.  Mol. Biol. Cell 15:  2729-2741.

Witman, G. B.   2003.  Cell Motility:  Deaf Drosophila keep the beat.  Curr. Bio. 13: R796-R798 (Dispatch).

Pazour, G. J. and G. B. Witman.  2003.  The vertebrate primary cilium is a sensory organelle.   Curr. Opin. Cell Biol. 15: 105-110.

Casey, D. M., T. Yagi, R. Kamiya and G. B. Witman.   2003.  DC3, the smallest subunit of the Chlamydomonas flagellar outer dynein arm-docking complex, is a redox-sensitive calcium-binding protein.  J. Biol. Chem.  278: 42652-42659.

Casey, D. M., G. J. Pazour, C. G. Wilkerson, K. Inaba, S. Takada, R. Kamiya and G. B. Witman.  2003.  DC3, the 21-kD subunit of the outer dynein arm-docking complex (ODA-DC), is a novel EF-hand protein important for assembly of both the outer arm and the ODA-DC.  Mol. Biol. Cell 14: 3650-3663.          

Rosenbaum, J. L. and G. B. Witman.  2002.  Intraflagellar transport.  Nat. Rev. Mol. Cell Biol. 3: 813-825.

Pazour, G. J., J. T. San Agustin, J. A. Follit, J. L. Rosenbaum, and G. B. Witman.  2002.  Polycystin-2 localizes to kidney cilia and the ciliary level is elevated in orpk mice with polycystic kidney disease.  Current Bio. 12: R378-R380.

Pazour, G. J., S. A. Baker, J. A. Deane, D. G. Cole, B. L. Dickert, J. L. Rosenbaum, G. B. Witman, and J. C. Besharse.  2002.  The intraflagellar transport protein, IFT88, is essential for vertebrate photoreceptor assembly and maintenance.  J. Cell Biol. 157: 103-113.  (Cover)

Takada, S., C. G. Wilkerson, K. Wakabayashi, R. Kamiya and G. B. Witman.   2002.  The outer dynein arm-docking complex:  composition and characterization of a subunit (Oda1) necessary for outer arm assembly.  Mol Biol. Cell. 13: 1015-1029.

Wakabayashi, K., S. Takada, G. B. Witman and R. Kamiya.  2001.  Transport and arrangement of the outer-dynein-arm docking complex in the flagella of Chlamydomonas mutants that lack outer dynein arms.  Cell Motil. Cytoskeleton 48: 277-286.

San Agustin, J. T. and G. B. Witman.   2001.  Differential expression of the C_s and Ca1 isoforms of the catalytic subunit of cyclic 3’,5’-adenosine monophosphate-dependent protein kinase in testicular cells.  Biol. Reprod. 65: 151-164.

Pazour, G. J., B. L. Dickert, Y. Vucica, E. S. Seeley, J. L. Rosenbaum, G. B. Witman and D. G. Cole.  2000.  Chlamydomonas IFT88 and its mouse homologue, polycystic kidney disease gene Tg737, are required for assembly of cilia and flagella.  J. Cell Biol. 151: 709-718.

Pazour, G. J. and G. B. Witman.  2000.  Forward and reverse genetic analysis of microtubule motors in Chlamydomonas.   Methods 22:285-298.

San Agustin, J. T., C. G. Wilkerson, and G. B. Witman.  2000.  The unique catalytic subunit (C_s) of sperm cAMP-dependent protein kinase is the product of an alternative Ca mRNA expressed specifically in spermatogenic cells.   Mol. Biol. Cell 11: 3031-3044.

[1]Pazour, G. J., A. Koutoulis, S. E. Benashski, B. L. Dickert, H. Sheng, R. S. Patel-King, S. M. King, and G. B. Witman.  1999.  LC2, the Chlamydomonas homologue of the t complex-encoded protein Tctex2, is essential for outer dynein arm assembly.  Mol Biol. Cell 10: 3507-3520.

Pazour, G. J., B. L. Dickert, and G. B. Witman.  1999.  The DHC1b isoform of cytoplasmic dynein is required for flagellar assembly.   J. Cell Biol. 144: 473-481. (Cover)

Omoto, C. K., I. R. Gibbons, R. Kamiya, C. Chingyoji, K. Takahashi, and G. B. Witman.  1999.  Rotation of the central-pair microtubules in eukaryotic flagella.  Mol Biol. Cell. 10: 1-4.

Rotation Projects

Potential rotation projects, several of which are described more fully in the Department of Cell Biology’s Research Rotations manual, include:

1.  Function of Primary Cilia

2.  Structure and Assembly of Dynein

3.  Intracellular Transport by Microtubule-Based Molecular Motors

4.  Role of Intraflagellar Transport (IFT) in Sperm Tail Formation

5.  Regulation of Dynein Motor Activity

6.  Identification of Cis-Acting Regulatory Elements for Genes Encoding Flagellar Proteins

Office: S7-117
Phone: 508-856-4038
Fax: 508-856-5612
E-mail: George.Witman@umassmed.edu
Keywords: Genetic Systems, Cell Motility, Cell Biology, Proteomics, Cytoskeleton

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