A secondary disruption of the dmpA gene encoding a large membrane protein allows aggregation defective Dictyostelium rasC- cells to form multicellular structures.
The disruption of the gene encoding the Dictyostelium Ras subfamily protein, RasC, results in a strain that does not aggregate and has defects in both cAMP signal relay and cAMP chemotaxis. Disruption of a second gene in the rasC(-) strain by Restriction Enzyme Mediated Integration produced cells that were capable of forming multicellular structures in plaques on bacterial lawns. The disrupted gene (dmpA) encoded a novel membrane protein that was designated Dmp1. Although the rasC(-)/dmpA(-) cells progressed through early development, they did not form aggregation streams on a plastic surface under submerged starvation conditions. Phosphorylation of PKB in response to cAMP, which is significantly reduced in rasC(-) cells, remained low in the rasC(-)/dmpA(-) cells. However, in spite of this low PKB phosphorylation, the rasC(-)/dmpA(-) cells underwent efficient chemotaxis to cAMP in a spatial gradient. Cyclic AMP accumulation, which was greatly reduced in the rasC(-) cells, was restored in the rasC(-)/dmpA(-) strain, but cAMP relay in these cells was not apparent. These data indicate that although the rasC(-)/dmpA(-) cells were capable of associating to form multicellular structures, normal aggregative cell signaling was clearly not restored. Disruption of the dmpA gene in a wild-type background resulted in cells that exhibited a slight defect in aggregation and a more substantial defect in late development. These results indicate that, in addition to the role played by Dmp1 in aggregation, it is also involved in late development.
Khosla
Meenal
M
Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, Canada V6T 1Z3.
Kriebel
Paul
P
Parent
Carole A
CA
Spiegelman
George B
GB
Weeks
Gerald
G
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D015139:Blotting, Southern; D002449:Cell Aggregation / Q000235:genetics; D002633:Chemotaxis / Q000235:genetics*; D000242:Cyclic AMP / Q000378:metabolism; D004023:Dictyostelium / Q000166:cytology* / Q000235:genetics* / Q000502:physiology; D017353:Gene Deletion; D017125:Genes, Protozoan; D016153:Genes, Suppressor; D008565:Membrane Proteins / Q000172:deficiency* / Q000235:genetics* / Q000502:physiology; D008969:Molecular Sequence Data; D010641:Phenotype; D010766:Phosphorylation; D017434:Protein Structure, Tertiary / Q000235:genetics; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000502:physiology; D018631:ras Proteins / Q000096:biosynthesis / Q000172:deficiency* / Q000235:genetics
D008565:Membrane Proteins; D015800:Protozoan Proteins; D000242:Cyclic AMP; D018631:ras Proteins