Expression of CSA-hm2 fusion in Dictyostelium discoideum under the control of the dictyostelium ras promoter reveals functional muscarinic receptors

: We have expressed the human m2 muscarinic receptor gene in the cellular slime mold Dictyostelium discoideum. Expression under the control of the constitutive actin 6 promoter without a D. discoideum leader peptide results in cells which seem to respond to muscarinic agonists initially, but which quickly revert to non responding cells only after a few generations. However, when expressing the hm2 gene as a fusion gene together with the CSA leader peptide under the control of the regulated D. discoideum ras promoter cells are obtained which express functional muscarinic M2 receptors in a stable manner. As expected from the typical regulation of the ras promoter, M2 receptors are expressed only during development. In ligand binding assays these heterologously expressed receptors show binding characteristics similar to authentic M2 receptors.