Overexpression of CAF1 encoding a novel Ca2+-binding protein stimulates the transition of Dictyostelium cells from growth to differentiation.
Among the expressed genes associated with the switch-over of Dictyostelium cells from cell proliferation to differentiation, the Calfumirin-1 (CAF1) gene has been shown to be preferentially expressed at the initial step of differentiation, encoding a novel Ca2+-binding protein (Abe & Maeda 1995). To analyze precisely the function of CAF1, transformants overexpressing the CAF1 mRNA at the vegetative growth phase and also CAF1-null mutants were prepared, and their developmental features were compared with those of parental wild-type cells. As a result, the CAF1-overexpression was found to promote cell differentiation, possibly through prompt induction of the cAMP receptor 1 (CAR1) gene expression. In addition, the CAF1-overexpressing cells were able to differentiate even under low external Ca2+ ([Ca2+]e) conditions around 10(-6) mol/L at which non-transformed wild-type cells never differentiated. Unexpectedly, however, the CAF1-null mutant produced by homologous recombination exhibited apparently normal development to form fruiting bodies on non-nutrient agar. These results seem to indicate that CAF1-overexpression has a stimulatory effect on differentiation, but that the CAF1 protein is not necessarily required for the phase-shift of cells from growth to differentiation.
Itoh
M
M
Biological Institute, Graduate School of Science, Tohoku University, Aoba, Sendai, Japan.
Noguchi
M
M
Maeda
Y
Y
D000818:Animals; D015152:Blotting, Northern; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000502:physiology; D002454:Cell Differentiation; D002455:Cell Division; D004023:Dictyostelium / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics; D015870:Gene Expression; D005822:Genetic Vectors; D009154:Mutation; D012313:RNA / Q000302:isolation & purification; D011953:Receptors, Cyclic AMP / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D014170:Transformation, Genetic
D002135:Calcium-Binding Proteins; D005656:Fungal Proteins; D011953:Receptors, Cyclic AMP; D014157:Transcription Factors; C068125:cyclic AMP receptor cAR1; D012313:RNA; D002118:Calcium