Developmental regulation of the Inositol 1,4,5-trisphosphate phosphatases in Dictyostelium discoideum

The cellular slime mold Dictyostelium discoideum is a microorganism in which growth and development are strictly separated. Starvation initiates a developmental program in which extracellular cAMP plays a major role as a signal molecule. In response to cAMP several second messengers are produced, including cAMP, cGMP and inositol 1,4,5-trisphosphate, (Ins(l,4,5)P 3). Ins(l,4,5)P 3 levels are controlled by the activation of phosphoinositidase C and the activity of the Ins(l,4,5)P 3-degrading phosphatases. In Dictyostelium discoideum two major routes for the dephosphorylation of Ins(l,4,5)P 3 are present: a 5-phosphatase, which hydrolyses Ins(l,4,5)P 3 at the 5-position producing Ins(l,4)P 2 as in vertebrate cells, and a 1-phosphatase which removes the 1-phosphate, giving Ins(4,5)P 2, as in plants. In this paper we show that at the onset of development both the 1-phosphatase and the 5-phosphatase are present in equal amounts. During development the 5-phosphatase disappears leaving the 1-phosphatase as the single enzyme to remove Ins(l,4,5)P 3. We conclude that during development Dictyostelium discoideum switches from a mixed type of Ins(l,4,5)P 3 degradation to a more plant-like degradation pathway.