Cell polarity, intercellular signalling and morphogenetic cell movements in Myxococcus xanthus

In Myxococcus xanthus morphogenetic cell movements constitute the basis for the formation of spreading vegetative colonies and fruiting bodies in starving cells. M. xanthus cells move by gliding and gliding motility depends on two polarly localized engines, type IV pili pull cells forward, and slime extruding nozzle-like structures appear to push cells forward. The motility behaviour of cells provides evidence that the two engines are localized to opposite poles and that they undergo polarity switching. Several proteins involved in regulating polarity switching have been identified. The cell surface-associated C-signal induces the directed movement of cells into nascent fruiting bodies. Recently, the molecular nature of the C-signal molecule was elucidated and the motility parameters regulated by the C-signal were identified. From the effect of the C-signal on cell behaviour it appears that the C-signal inhibits polarity switching of the two motility engines. This establishes a connection between cell polarity, signalling by an intercellular signal and morphogenetic cell movements during fruiting body formation.