A SLOW SUSTAINED INCREASE IN CYTOSOLIC CA2-INDUCING FACTOR IN DICTYOSTELIUM( LEVELS MEDIATES STALK GENE INDUCTION BY DIFFERENTIATION)

During Dictyostelium stalk cell differentiation, cells vacuolate, synt hesize a cellulose cell wall and die. This process of programmed cell death is accompanied by expression of the prestalk gene ecmB and induc ed by the differentiation inducing factor DIF. Using cell lines expres sing the recombinant Ca2+-sensitive photoprotein apoaequorin, we found that 100 nM DIF increases cytosolic Ca2+ ([Ca2+](i)) levels from simi lar to 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 t he same level as DIF. The [Ca2+](i) increases induced by DIF and BHQ s howed similar kinetics and preceded ecmB gene expression by similar to 1-2 h. The Ca2+ chelator 1,2-bis(o-aminophenoxy)-ethane-N,N,N'N' -tet ra-acetic acid (BAPTA) efficiently inhibited the BHQ-induced [Ca2+](i) increase and blocked DLF-induced expression of the ecmB gene, These d ata indicate that the effects of DIF on stalk gene expression are medi ated by a sustained increase in [Ca2+](i). Sustained [Ca2+](i) elevati on mediates many forms of programmed cell death in vertebrates, The Di ctyostelium system may be the earliest example of how this mechanism d eveloped during early eukaryote evolution.