Lithium-Induced respecification of pattern in Paramecium

The long-known teratogenic effects (dorsalisation) of lithium on amphibian embryos has recently raised renewed interest. As it is known that lithium blocks the polyphosphoinositide (PI) cycle, causing a depressed level of myo-inositol, and as injections of myo-inostiol have been shown to rescue the effects of Li+, it was postulated that Li+ causes a flattening of gradients of PI cycle activity underlying the developmental polarities. We have studied the effect of Li+ on the morphogenesis of the unicellular organism, Paramecium. We show (1) that exposure to 25 mM Li+ during division yields precise distorsions of the cortical pattern that can be explained by a uniformisation of surface growth i.e. partial suppression of the right/left and antero/posterior asymmetries and (2) that Li+ effects are rescued by injection of myo- inositol. These results suggest that spatially graded activity of the PI cycle (ensuring in turn a spatially graded distribution of secondary messengers directly involved in the morphogenetic processes) appeared early in evolution. © 1992 Wiley-Liss, Inc.