Involvements of a novel protein, DIA2, in cAMP signaling and spore differentiation during Dictyostelium development

The novel gene dia2 (differentiation-associated gene 2) was originally isolated as a gene expressed specifically in response to initial differentiation of Dictyostelium discoideum Ax-2 cells. Using dia2AS cells in which the dia2 expression was inactivated by the antisense RNA method, DIA2 protein was found to be required for cAMP signaling during cell aggregation. During late development, the DIA2 protein changed its location from the endoplasmic reticulum (ER) to prespore-specific vacuoles (PSVs) that are specifically present in prespore cells of the slug. In differentiating prestalk cells, however, DIA2 was found to be nearly lost from the cells. Importantly, exocytosis of PSVs from prespore cells and the subsequent spore differentiation were almost completely impaired in dia2AS cells. In addition, spore induction by externally applied 8-bromo cAMP was significantly suppressed in dia2AS cells. Taken together, these results strongly suggested that DIA2 might be closely involved in cAMP signaling and spore differentiation as well as in the initiation of differentiation during Dictyostelium development.