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Manuel Haynes

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started by Manuel Haynes on 19 May 12
  • Manuel Haynes
     
    screens, which are aided by collaborative efforts currently underway to
    mutate all coding genes in mouse, fly, and worm using various methods (see
    the databases and Web resources listed in Table 1.1). Screens in the different
    model systems have complemented one another and generated data sets that
    are overlapping but not identical. This may be in part because of the sensitivi-
    ty of the phenotypes scored and the types of mutation (e.g., loss-of-function
    versus hypomorphic alleles) introduced in each system. However, studies of
    the Hh signaling pathway have suggested that some species-specific mechan-
    isms are used to transduce cell-cell signals. Free medical books

    Key components of the Hh pathway are highly conserved (reviewed in
    Lum and Beachy, 2004; Huangfu and Anderson, 2005b). Hh signal transduc-
    tion is controlled by the actions of the Patched (Ptc) receptor and the seven-
    pass transmembrane protein, Smoothened (Smo). In the absence of Hh, Ptc
    inhibits Smo from transducing signals. Hh binding to Ptc relieves this inhibi-
    tion and enables Smo to activate a cytoplasmic signal transduction pathway
    that culminates in the proteolysis and nuclear translocation of an activating
    transcription factor (known as Gli in vertebrates and Ci in Drosophila). In
    mice, ENU mutagenesis screens identified cilia and intraflagellar transport
    proteins as essential components of the Hh pathway that act downstream of
    Ptc and Smo (Huangfu et al., 2003; Huangfu and Anderson, 2005a). Func-
    tional studies have demonstrated that activation of the Hh pathway in verte-
    brates induces the localization of Smo, Gli2 and Gli3, and other relevant
    proteins to cilia; a cilia localization motif on Smo is essential for normal Hh
    responses in cultured cells and zebrafish (Corbit et al., 2005; Haycraft et al.,
    2005). By contrast, intraflagellar transport mutations do not cause Hh-like
    phenotypes in Drosophila, and, in this organism, Hh-responsive cells do not
    have cilia (Ray et al., 1999; Han et al., 2003; Avidor-Reiss et al., 2004).
    Drosophila Smo accumulates at the plasma membrane upon Hh stimulation,
    whereas the vertebrate ortholog gets internalized. Furthermore, mammalian
    and fly Smo proteins are phosphorylated on different residues in response to
    Hh. Phosphorylation is required for the internalization of mammalian Smo
    RNAi uses short, double-stranded RNAs to trigger the degradation of tar-
    get mRNAs species. This was developed as an experimental tool for work
    with C. elegans, in which it is now widely used for loss-of-function studies
    and phenotype-driven screens (Fire et al., 1998; Wang and Barr, 2005).
    Recently, genome-wide screens have been developed that use RNAi in Dro-
    sophila embryonic imaginal disc cell cultures (clone-8 cells) to identify novel
    signaling pathway components (Lum et al., 2003). In these screens, clone-
    8 cells are cotransfected with a pathway-responsive luciferase reporter and a

    proteoglycan (Dally-like, which was previously implicated in Wnt signaling),
    a homeodomain gene, three kinases (CK1 , Pitslre1, and Cdk9), and a phos-
    phatase (PP2A). Interestingly, the screens also indicated that the Hh pathway
    is affected by factors involved in more general cellular processes, including
    ribosome and proteosome function, RNA regulation and splicing, and vesicle

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