Andrew Wilkins,1,5Meenal
Khosla,2,5 Derek J.
Fraser,3,5 George
B. Spiegelman,2Paul
R. Fisher,3
Gerald Weeks,2and
Robert H. Insall 4,6
1 MRC Laboratory for Molecular
Cell Biology and Departments of Physiology, University College London,
London WC1E
6BT, UK; 2 Department
of Microbiology and Immunology and Department of Medical Genetics, University
of British
Columbia, Vancouver V6T 1Z3, Canada; 3
Department
of Microbiology, La Trobe University, Bundoora, Victoria 3083,
Australia; 4 School
of Biosciences, Birmingham University, Edgbaston, Birmingham B15 2TT, UK
RasD, a Dictyostelium homolog of mammalian Ras,
is maximally expressed during the multicellular stage of
development. Normal Dictyostelium aggregates
are phototactic and thermotactic, moving towards sources of
light and heat with great sensitivity. We show that
disruption of the gene for rasD causes a near-total loss of
phototaxis and thermotaxis in mutant aggregates, without
obvious effects on undirected movement. Previous
experiments had suggested important roles for RasD
in development and cell-type determination. Surprisingly,
rasD - cells show no obvious changes in these
processes. These cells represent a novel class of phototaxis
mutant, and indicate a role for a Ras pathway in the
connections between stimuli and coordinated cell
movement.
[Key Words: Phototaxis; Dictyostelium;
oncogenes; Ras; small GTPases]
Received January 10, 2000; revised
version accepted April 7, 2000.