The myosin II activator Rho-kinase (Rok) is planar polarized at the tissue boundary of the Drosophila embryonic salivary gland placode through a negative regulation by the apical polarity protein Crumbs that is anisotropically localized at the boundary. However, in inner cells of the placode, both Crumbs and Rok are isotropically enriched at junctions. We propose that modulation of Rok membrane residence time by Crumbs’ downstream effectors can reconcile both behaviors. Using FRAP combined with in silico simulations, we find that the lower membrane dissociation rate (k off) of Rok at the tissue boundary with low Crumbs explains this boundary-specific effect. The S/T kinase Pak1, recruited by Crumbs and Cdc42, negatively affects Rok membrane association in vivo and in vitro can phosphorylate Rok near the pleckstrin homology (PH) domain that mediates membrane association. These data reveal an important mechanism of the modulation of Rok membrane residence time via affecting the k off that may be widely employed during tissue morphogenesis.
Rho-kinase is planar polarized at tissue boundaries, complementary to Crumbs
Crumbs and downstream Pak1 modulate Rok residence time by affecting k off
Pak1 can phosphorylate Rok near the PH and Rho-binding domains
Rok phosphorylation affects residence time and allows polarization at boundaries
Sidor et al. show that a modulation of Rok’s k off through phosphorylation of its membrane association regions by Pak1 downstream of Crumbs can drive planar polarization of Rok at tissue boundaries.