EXPRESSION OF CAMP-DEPENDENT PROTEIN-KINASE IN PRESPORE CELLS IS SUFFICIENT TO INDUCE SPORE CELL-DIFFERENTIATION IN DICTYOSTELIUM

The activity of cAMP-dependent protein ki nase (PKA) is required for proper development at several stages during the Dictyostelium life cycle. We present evidence that activation of PKA is rate-limiting for the differentiation of prespore cells to spores and that PKA activation may be the developmental trigger for sporulation. Strains that overexpress the gene encoding the catalytic subunit of PKA (PKAcat) of lack a functional regulatory subunit (rdeC strains) undergo rapid, heterochronic development. We show that overexpression of PKAcat in prespore cells is sufficient to directly induce expression of the spore maturation marker spiA and differentiation to spores, in a cell-autonomous manner. Moreover, overexpression of PKAcat in prespore cells can bypass a mutation that blocks an earlier developmental step to induce spiA expression. Our results suggest that the regulatory pathway in prespore cells between the activation of PKA and spiA induction/spore maturation is quite short and that PKAcat expression in prespore cells may mediate spore differentiation at the level of transcription. This induction of sporulation requires the prior activation of the prespore cell pathway. In addition, we show that B-galactosidase activity expressed from a PKAcat promoter/lacZ reporter construct is highly enriched in the anterior prestalk A region during the tipped aggregate, slug, acid early culminant stages and that this pattern switches abruptly to a prespore pattern at the time of spore maturation, supporting the proposed role of PKA in this process.