IDENTIFICATION OF NOVEL SIGNALING PATHWAY COMPONENTS - 0 views

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  #1 Manuel Haynes on 19 May 12

   

  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
  
  

   

  <div class="cArrow"> </div><div class="cContentInner">screens, which are aided by collaborative efforts currently underway to<br />mutate all coding genes in mouse, fly, and worm using various methods (see<br />the databases and Web resources listed in Table 1.1). Screens in the different<br />model systems have complemented one another and generated data sets that<br />are overlapping but not identical. This may be in part because of the sensitivi-<br />ty of the phenotypes scored and the types of mutation (e.g., loss-of-function<br />versus hypomorphic alleles) introduced in each system. However, studies of<br />the Hh signaling pathway have suggested that some species-specific mechan-<br />isms are used to transduce cell-cell signals. <a rel="nofollow" href="http://www.mediebooks.com/">Free medical books</a><br /><br />Key components of the Hh pathway are highly conserved (reviewed in<br />Lum and Beachy, 2004; Huangfu and Anderson, 2005b). Hh signal transduc-<br />tion is controlled by the actions of the Patched (Ptc) receptor and the seven-<br />pass transmembrane protein, Smoothened (Smo). In the absence of Hh, Ptc<br />inhibits Smo from transducing signals. Hh binding to Ptc relieves this inhibi-<br />tion and enables Smo to activate a cytoplasmic signal transduction pathway<br />that culminates in the proteolysis and nuclear translocation of an activating<br />transcription factor (known as Gli in vertebrates and Ci in Drosophila). In<br />mice, ENU mutagenesis screens identified cilia and intraflagellar transport<br />proteins as essential components of the Hh pathway that act downstream of<br />Ptc and Smo (Huangfu et al., 2003; Huangfu and Anderson, 2005a). Func-<br />tional studies have demonstrated that activation of the Hh pathway in verte-<br />brates induces the localization of Smo, Gli2 and Gli3, and other relevant<br />proteins to cilia; a cilia localization motif on Smo is essential for normal Hh<br />responses in cultured cells and zebrafish (Corbit et al., 2005; Haycraft et al.,<br />2005). By contrast, intraflagellar transport mutations do not cause Hh-like<br />phenotypes in Drosophila, and, in this organism, Hh-responsive cells do not<br />have cilia (Ray et al., 1999; Han et al., 2003; Avidor-Reiss et al., 2004).<br />Drosophila Smo accumulates at the plasma membrane upon Hh stimulation, <br />whereas the vertebrate ortholog gets internalized. Furthermore, mammalian<br />and fly Smo proteins are phosphorylated on different residues in response to<br />Hh. Phosphorylation is required for the internalization of mammalian Smo<br />RNAi uses short, double-stranded RNAs to trigger the degradation of tar-<br />get mRNAs species. This was developed as an experimental tool for work<br />with C. elegans, in which it is now widely used for loss-of-function studies<br />and phenotype-driven screens (Fire et al., 1998; Wang and Barr, 2005). <br />Recently, genome-wide screens have been developed that use RNAi in Dro-<br />sophila embryonic imaginal disc cell cultures (clone-8 cells) to identify novel<br />signaling pathway components (Lum et al., 2003). In these screens, clone-<br />8 cells are cotransfected with a pathway-responsive luciferase reporter and a<br /> <br />proteoglycan (Dally-like, which was previously implicated in Wnt signaling),<br />a homeodomain gene, three kinases (CK1 , Pitslre1, and Cdk9), and a phos-<br />phatase (PP2A). Interestingly, the screens also indicated that the Hh pathway<br />is affected by factors involved in more general cellular processes, including<br />ribosome and proteosome function, RNA regulation and splicing, and vesicle <br /><br /></div>

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