title: RasG signaling is important for optimal folate chemotaxis in Dictyostelium.
abstract: BACKGROUND
  Signaling pathways linking receptor activation to actin reorganization and pseudopod dynamics during chemotaxis are arranged in complex networks. Dictyostelium discoideum has proven to be an excellent model system for studying these networks and a body of evidence has indicated that RasG and RasC, members of the Ras GTPase subfamily function as key chemotaxis regulators. However, recent evidence has been presented indicating that Ras signaling is not important for Dictyostelium chemotaxis. In this study, we have reexamined the role of Ras proteins in folate chemotaxis and then, having re-established the importance of Ras for this process, identified the parts of the RasG protein molecule that are involved.
  
  
  RESULTS
  A direct comparison of folate chemotaxis methodologies revealed that rasG-C- cells grown in association with a bacterial food source were capable of positive chemotaxis, only when their initial position was comparatively close to the folate source. In contrast, cells grown in axenic medium orientate randomly regardless of their distance to the micropipette. Folate chemotaxis is restored in rasG-C- cells by exogenous expression of protein chimeras containing either N- or C- terminal halves of the RasG protein.
  
  
  CONCLUSIONS
  Conflicting data regarding the importance of Ras to Dictyostelium chemotaxis were the result of differing experimental methodologies. Both axenic and bacterially grown cells require RasG for optimal folate chemotaxis, particularly in weak gradients. In strong gradients, the requirement for RasG is relaxed, but only in bacterially grown cells. Both N- and C- terminal portions of the RasG protein are important for folate chemotaxis, suggesting that there are functionally important amino acids outside the well established switch I and switch II interaction surfaces.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, 1365, Life Sciences Centre 2350, Health Sciences Mall, V6T 1Z3 Vancouver, BC, Canada. alexchat@mail.ubc.ca.
authors.forename: Alex
authors.initials: A
authors.lastname: Chattwood
authors.forename: Parvin
authors.initials: P
authors.lastname: Bolourani
authors.forename: Gerald
authors.initials: G
authors.lastname: Weeks
mesh_terms: D002633:Chemotaxis; D004023:Dictyostelium / Q000166:cytology / Q000254:growth & development / Q000502:physiology*; D005492:Folic Acid / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism*; D015398:Signal Transduction; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D015800:Protozoan Proteins; C424065:rasG protein, Dictyostelium; D005492:Folic Acid; D018631:ras Proteins
references.citation: Mol Biol Cell. 2006 Oct;17(10):4543-50
references.pmid: 16885420
references.citation: J Cell Sci. 2000 Feb;113 ( Pt 4):709-19
references.pmid: 10652263
references.citation: J Cell Biol. 2014 Feb 17;204(4):497-505
references.pmid: 24535823
references.citation: Dev Cell. 2010 May 18;18(5):737-49
references.pmid: 20493808
references.citation: EMBO J. 2001 Aug 15;20(16):4490-9
references.pmid: 11500376
references.citation: Curr Biol. 2008 Oct 28;18(20):1587-1593
references.pmid: 18948008
references.citation: J Cell Sci. 2013 Sep 15;126(Pt 18):4296-307
references.pmid: 23843627
references.citation: J Cell Sci. 2013 Jan 1;126(Pt 1):221-33
references.pmid: 23132928
references.citation: EMBO Rep. 2004 Jun;5(6):602-6
references.pmid: 15143344
references.citation: Methods Mol Biol. 2009;571:473-88
references.pmid: 19763986
references.citation: Genes Dev. 1991 Jan;5(1):9-21
references.pmid: 1703508
references.citation: Exp Cell Res. 2005 May 15;306(1):47-55
references.pmid: 15878331
references.citation: Methods Cell Biol. 1987;28:157-76
references.pmid: 3600405
references.citation: Curr Opin Neurobiol. 1999 Jun;9(3):355-63
references.pmid: 10395576
references.citation: Curr Biol. 2014 Feb 17;24(4):415-21
references.pmid: 24485835
references.citation: Eukaryot Cell. 2010 Nov;9(11):1728-33
references.pmid: 20833893
references.citation: Proc Natl Acad Sci U S A. 2007 Oct 9;104(41):15988-93
references.pmid: 17905871
references.citation: J Biol Chem. 2010 Dec 31;285(53):41374-9
references.pmid: 20971846
references.citation: Nat New Biol. 1972 Jun 7;237(75):181-2
references.pmid: 4504203
references.citation: J Cell Biol. 1997 Aug 11;138(3):605-14
references.pmid: 9245789
references.citation: Nature. 2013 May 30;497(7451):638-42
references.pmid: 23698361
references.citation: EMBO Rep. 2011 Dec 01;12(12):1273-9
references.pmid: 22081140
references.citation: J Cell Biol. 2004 Nov 8;167(3):505-18
references.pmid: 15534002
references.citation: Methods Enzymol. 2012;504:183-200
references.pmid: 22264535
references.citation: Curr Biol. 2008 Jul 22;18(14):1034-43
references.pmid: 18635356
references.citation: J Cell Sci. 2000 Apr;113 ( Pt 8):1427-34
references.pmid: 10725225
references.citation: Int Rev Cell Mol Biol. 2008;271:253-300
references.pmid: 19081545
references.citation: Cell. 2002 May 31;109(5):611-23
references.pmid: 12062104
references.citation: Annu Rev Biophys. 2010;39:265-89
references.pmid: 20192768
references.citation: Bioorg Med Chem Lett. 2012 Sep 15;22(18):5766-76
references.pmid: 22902659
references.citation: J Cell Sci. 2013 Oct 1;126(Pt 19):4502-13
references.pmid: 23886948
references.citation: J Cell Biol. 2008 Feb 25;180(4):747-53
references.pmid: 18299345
references.citation: Int J Dev Biol. 2012;56(4):263-72
references.pmid: 22252537