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One or more keywords matched the following properties of Witman, George
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Cilia and Flagella, Molecular Motors, Sensory Transduction, Proteomics, Molecular Basis for Diseases Involving Cilia and Flagella

Our research is concerned with the biology of cilia and flagella, including the non-motile primary cilia that are present on most cells in our bodies and function as cell antennae, receiving signals from the environment and transmitting these to the cell body. Our findings have important implications for human development and male infertility, and for diseases of the lung, kidney, and eye, all of which contain cilia. Such diseases are known as "ciliopathies."

In many of these studies we are using the unicellular Chlamydomonas, a model flagellated organism amenable to biochemical, genetic, and molecular genetic approaches. We recently completed a proteomic analysis of the Chlamydomonas flagellum. This has resulted in a virtual "gold mine" of data that has and will continue to 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 ciliary proteins. We currently are investigating the functions of several proteins whose homologues in humans or mice are known to cause disease, including blindness (Leber congenital amaurosis), cystic kidney disease, hydrocephalus, and syndromic ciliopathies such as Bardet-Biedl syndrome and primary ciliary dyskinesia. Typically, we explore the functions of these proteins in Chlamydomonas and then in the mouse to be sure that what we learn from Chlamydomonas is applicable to mammals.

In addition, many members of this laboratory are participating in a large-scale project to generate and identify insertional Chlamydomonas mutants for all the genes encoding flagellar proteins. Chlamydomonas cells are transformed with a selectable marker that integrates at random into the genome, disrupting any gene at the site of insertion. Using PCR, we can then readily determine the genomic sequence flanking the insert, and thus identify the mutated gene. The mutant can then be characterized structurally and biochemically to understand the function of the mutated gene.

Finally, we 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. 1). These particles carry cargo necessary for assembly and maintenance of the cilium or flagellum, and also transport signals from the cilium or flagellum to the cell body and vice versa (Fig. 2). We are characterizing the motors responsible for this transport, the individual polypeptides that make up the IFT particles, and the proteins and protein complexes that interact with the IFT particle and generally function as cargo adaptors. These studies are providing new insights into a process that is essential for the assembly of almost all cilia and flagella.

Witman Figure 1 a

Figure 1. The intraflagellar transport (IFT) machinery. During IFT, linear arrays of IFT particles (yellow) are transported towards the 'plus' (distal) ends of the flagellar outer doublet microtubules (blue) by kinesin-II (pink), and towards the 'minus' (proximal) ends of the microtubules by cytoplasmic dynein 1b (green). The IFT particles, which are composed of at least 19 different proteins, are believed to be carrying precursors that are necessary for the assembly of the flagellar axoneme. The IFT particles are linked to the flagellar membrane (grey lines), and there is evidence that their cargo also includes membrane proteins.

Witman Figure 2

Figure 2. IFT and targeting of proteins to the flagellar compartment. Flagellar membrane proteins are carried by vesicles from the Golgi apparatus to the base of the flagellum, where they fuse with the plasma membrane of the cell. In this figure, proteins destined for the flagellar membrane are sorted into specific vesicles that are then targeted to the base of the flagellum. This sorting and targeting appears to be aided by one or more IFT-particle proteins that cycle from the base of the flagellum back through the endomembrane system, where they become associated with the proteins that are destined for the flagellar membrane. Once the vesicle is exocytosed, the IFT-particle proteins, with attached flagellar membrane proteins, become incorporated into IFT particles and are moved through the flagellar pore (involving outer doublet-membrane links in the flagellar transition zone) into the flagellar compartment.

One or more keywords matched the following items that are connected to Witman, George
Item TypeName
Academic Article A FAP46 mutant provides new insights into the function and assembly of the C1d complex of the ciliary central apparatus.
Academic Article Isolation of Chlamydomonas flagella and flagellar axonemes.
Academic Article Calcium control of waveform in isolated flagellar axonemes of Chlamydomonas.
Academic Article IC97 is a novel intermediate chain of I1 dynein that interacts with tubulin and regulates interdoublet sliding.
Academic Article The Chlamydomonas reinhardtii BBSome is an IFT cargo required for export of specific signaling proteins from flagella.
Academic Article Total internal reflection fluorescence (TIRF) microscopy of Chlamydomonas flagella.
Academic Article Isolation of Chlamydomonas flagella.
Academic Article Role of calmodulin in the flagellar axoneme: effect of phenothiazines on reactivated axonemes of Chlamydomonas.
Concept Axoneme
Academic Article Cooperative binding of the outer arm-docking complex underlies the regular arrangement of outer arm dynein in the axoneme.
Academic Article In situ localization of N and C termini of subunits of the flagellar nexin-dynein regulatory complex (N-DRC) using SNAP tag and cryo-electron tomography.
Academic Article Reduced tubulin polyglutamylation suppresses flagellar shortness in Chlamydomonas.
Academic Article Intraflagellar transport is essential for mammalian spermiogenesis but is absent in mature sperm.
Academic Article A microtubule-dynein tethering complex regulates the axonemal inner dynein f (I1).
Academic Article The N-terminus of IFT46 mediates intraflagellar transport of outer arm dynein and its cargo-adaptor ODA16.
Academic Article A global analysis of IFT-A function reveals specialization for transport of membrane-associated proteins into cilia.
Academic Article Proteome of the central apparatus of a ciliary axoneme.
Academic Article Structural organization of the C1a-e-c supercomplex within the ciliary central apparatus.
Academic Article The unity and diversity of the ciliary central apparatus.
Academic Article Diffusion rather than intraflagellar transport likely provides most of the tubulin required for axonemal assembly in Chlamydomonas.
Academic Article Chlamydomonas FAP70 is a component of the previously uncharacterized ciliary central apparatus projection C2a.
Academic Article Structural organization of the C1b projection within the ciliary central apparatus.
Academic Article Consensus nomenclature for dyneins and associated assembly factors.
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  • Axoneme