Fig. 1.

The Fog Signaling Pathway. Fog is a large secreted protein which acts as a ligand for Mist, a seven pass transmembrane GPCR. In its ligand-free state Mist is predicted to interact with inactive, GDP-bound Cta. Once Fog binds Mist, it likely stimulates Cta's exchange of GTP for GDP, which allows Cta to dissociate from its trimer partners, Gβ and Gγ. Cta-GTP binds to RhoGEF2 which can then act as a GEF for Rho1. In its GTP-bound form Rho1 then activates Rok. Finally, the regulatory light chain of non-muscle myosin II, Spaghetti squash, is phosphorylated by active Rok to induce apical actomyosin network contraction in the cells which receive the Fog signal. Boxed are vertebrate components of Rho axis signaling which act in a similar manner to induce actomyosin cytoskeleton rearrangements. In vertebrates, Rok is known to phosphorylate many proteins which interact with actin, activating some and inactivating others.