SPATIAL AND TEMPORAL EXPRESSION OF THE DICTYOSTELIUM-DISCOIDEUM G-ALPHA PROTEIN SUBUNIT G-ALPHA-2 - EXPRESSION OF A DOMINANT-NEGATIVE PROTEIN INHIBITS PROPER PRESTALK TO STALK DIFFERENTIATION

Previous results have shown that the Got protein subunit G alpha 2 is required for aggregation in Dictyostelium discoideum and is essential for coupling cell-surface cAMP receptors to downstream effecters in vi vo during this stage of development. G alpha 2 expresses at least four distinct transcripts that are differentially regulated during develop ment; two of the transcripts are expressed exclusively in the multicel lular stages and their expression is restricted to prestalk cells. We partially dissected the G alpha 2 promoter and identified a component that is expressed exclusively during the multicellular stages using lu ciferase gene fusions. When this promoter region is coupled to lacZ, b eta-gal expression is restricted to the multicellular stages and local ized in prestalk cells with a pattern similar to that of the ecmA pres talk-specific promoter. We show that expression in wild-type cells of the G alpha 2 mutant protein [G alpha 2(G206T)] during the early stage s of development blocks aggregation and cAMP-mediated activation of ad enylyl cyclase and guanylyl cyclase, suggesting it functions as a domi nant negatively active G alpha subunit. When this mutant G alpha prote in is expressed from the ecmA prestalk-specific promoter, abnormal sta lk differentiation during culmination is observed. Expression of the m utant G alpha 2 from the SP60 prespore promoter or wild-type G alpha 2 from either the ecmA or the SP60 promoter results in no detectable ph enotype. The results suggest that G alpha 2 plays an essential role du ring the culmination stage in prestalk cells and may mediate cAMP rece ptor activation of these processes during multicellular development.