Disruption of the gene encoding the cell adhesion molecule DdCAD-1 leads to aberrant cell sorting and cell-type proportioning during Dictyostelium development.
The cadA gene in Dictyostelium encodes the Ca2+-dependent cell adhesion molecule DdCAD-1, which is expressed soon after the initiation of development. To investigate the biological role of DdCAD-1, the cadA gene was disrupted by homologous recombination. The cadA-null cells showed a 50% reduction in EDTA-sensitive cell adhesion. The remaining EDTA-sensitive adhesion sites were resistant to dissociation by anti-DdCAD-1 antibody, suggesting that they were distinct adhesion sites. Cells that lacked DdCAD-1 were able to complete development and form fruiting bodies. However, they displayed abnormal slug morphology and culmination was delayed by approximately 6 hours. The yield of spores was reduced by approximately 50%. The proportion of prestalk cells in cadA(-) slugs showed a 2.5-fold increase over the parental strain. When cadA(-) cells were transfected with pcotB::GFP to label prespore cells, aberrant cell-sorting patterns in slugs became apparent. When mutant prestalk cells were mixed with wild-type prespore cells, mutant prestalk cells were unable to return to the anterior position of chimeric slugs, suggesting defects in the sorting mechanism. The wild-type phenotype was restored when cadA(-) cells were transfected with a cadA-expression vector. These results indicate that, in addition to cell-cell adhesion, DdCAD-1 plays a role in cell type proportioning and pattern formation.
Banting and Best Department of Medical Research and Department of Biochemistry, University of Toronto, Toronto, Ontario M5G 1L6, Canada.
Estella
E
Wong
Chunzhong
C
Yang
Jun
J
Wang
Danny
D
Fuller
William F
WF
Loomis
Chi-Hung
CH
Siu
D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000502:physiology; D002448:Cell Adhesion / Q000187:drug effects; D015815:Cell Adhesion Molecules / Q000235:genetics* / Q000502:physiology; D004023:Dictyostelium / Q000166:cytology / Q000235:genetics* / Q000254:growth & development*; D004492:Edetic Acid / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental; D018390:Gene Targeting; D017125:Genes, Protozoan; D010641:Phenotype; D013170:Spores / Q000166:cytology; D014162:Transfection
D002135:Calcium-Binding Proteins; D015815:Cell Adhesion Molecules; C100604:DdCAD-1 protein, Dictyostelium discoideum; D004492:Edetic Acid