Effect of Retinal on <i>Dictyostelium</i> Cells During Development

Retinal plays a key role in light absorption across prokaryotes and eukaryotes, both in rhodopsin and bacteriorhodopsin systems. The multicellular social amoeba Dictyostelium discoideum exhibits positive phototaxis. However, retinal binding proteins such as rhodopsin have not been found in the genome of Dictyostelium cells. Herein, we microscopically examined the effects of retinal on Dictyostelium cells. On adding all-trans-retinal to the medium, Dictyostelium cells retracted their pseudopodia and became rounded. This was unique to retinal among the tested vitamin A variants. Addition of all-trans-retinal at low concentrations did not cause cell rounding. However, it increased the frequency of cAMP signaling triggered during cell development. Results indicate that retinal acts on an unknown signaling pathway involving the cytoskeleton in Dictyostelium cells.