SWITCHING OF CHEMOATTRACTANT RECEPTORS PROGRAMS DEVELOPMENT AND MORPHOGENESIS IN DICTYOSTELIUM - RECEPTOR SUBTYPES ACTIVATE COMMON RESPONSES AT DIFFERENT AGONIST CONCENTRATIONS

One of the common functional features among G-protein coupled receptor s is the occurrence of multiple subtypes involved in similar signal tr ansduction events. The cAMP chemoattractant receptor family of Dictyos telium discoideum is composed of four receptors (cAR1-cAR4), which are expressed sequentially throughout the developmental transition from a unicellular to a multicellular organism. The receptors differ in affi nity for cAMP and in the sequences of their C-terminal domains. In thi s study, we constitutively expressed cAR1, cAR2, and cAR3 as well as a series of chimeric and mutant receptors and assessed the capacity of each to mediate chemotaxis, activation of adenylyl cyclase and actin p olymerization, and rescue the developmental defect of car1(-)/car3(-) cells. We found that various receptors and mutants sense different con centration ranges of cAMP but all can mediate identical responses duri ng the aggregation stage of development. The responses displayed very similar kinetics, suggesting no major differences in regulatory proper ties attributable to the C-terminal domains. We speculate that switchi ng of receptor subtypes during development enables the organism to res pond to the changing concentrations of the chemoattractant and thereby program morphogenesis appropriately. (C) 1998 Academic Press.