A slow sustained increase in cytosolic Ca2+ levels mediates stalk gene induction by differentiation inducing factor in Dictyostelium. |
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| Authors: | P Schaap T Nebl and P R Fisher |
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| Affiliation: | Cell Biology Section, Institute for Molecular Plant Sciences, Clusius Laboratory, University of Leiden, The Netherlands. |
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| Abstract: | During Dictyostelium stalk cell differentiation, cells vacuolate, synthesize a cellulose cell wall and die. This process of programmed cell death is accompanied by expression of the prestalk gene ecmB and induced by the differentiation inducing factor DIF. Using cell lines expressing the recombinant Ca2+-sensitive photoprotein apoaequorin, we found that 100 nM DIF increases cytosolic Ca2+ (Ca2+]i) levels from approximately 50 to 150 nM over a period of 8 h. The Ca2+-ATPase inhibitor 2,5-di(tert-butyl)-1,4-hydroquinone (BHQ) induced a similar increase in Ca2+]i levels and induced expression of the prestalk gene ecmB to the same level as DIF. The Ca2+]i increases induced by DIF and BHQ showed similar kinetics and preceded ecmB gene expression by approximately 1-2 h. The Ca2+ chelator 1,2-bis(o-aminophenoxy)-ethane-N,N,N'N'-tetra-acetic acid (BAPTA) efficiently inhibited the BHQ-induced Ca2+]i increase and blocked DIF-induced expression of the ecmB gene. These data indicate that the effects of DIF on stalk gene expression are mediated by a sustained increase in Ca2-]i. Sustained Ca2+]i elevation mediates many forms of programmed cell death in vertebrates. The Dictyostelium system may be the earliest example of how this mechanism developed during early eukaryote evolution. |
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