Hippo-RhoG Signaling Maintains Directional Migration Cell Polarity In Caenorhabditis Elegans

Directional cell migration plays essential roles in organism development,immune responses,wound healing as well as cancer invasion and metastasis.Disruptions in precise location of cortical neurons lead to cortical development malformation and neuropsychiatric diseases including schizophrenia and autism.It has been well established that actin and actin regulators based migration machinery couples with cell intrinsic polarity and extracellular guidance cues to facilitate directional cell migration.Rac,one of the small Rho GTPase,is the regulation center for Arp2/3 mediated branched F-actin cytoskeleton during cell migration.However,Rho GTPase is evenly distributed on the cell cortex while their activity is rigorously restricted to the leading edge only.It is imperative to uncover the spatial temporal regulation mechanisms on Rho GTPase activity and further explain the complex regulation network on directional cell migtation.In this study,we report a new mechanism that Hippo kinase,independent of the classic Hippo signaling pathway,to regulate Q neuroblast migration in C.elegans.By using of the CRISPR-Cas9 based genome editing technology,we construct multiple alleles of cst-1 and cst-2,the Hippo homologues in C.elegans,single and double mutants,and uncover that loss of Hippo kinases lead to ectopic Dorsal Ventral polarization and migration of Q cells that is Anterior and Posterior specific in WT worms.This ectopic DV polarization mimics the defects in MIG-2/RhoG gain of function mutants.Via protein mass spectrum and in vitro kinase assay,we identify that Hippo kinase phosphorylates MIG-2/RhoG on the Ser139 that decreases MIG-2/RhoG activity on the regulation of F-actin accumulation,lamellipodium formation and finally cell migration.Hippo kinases are asymmetrically localized in migrating cell that reside in cell periphery and rear but are absent from the leading edge.Interestingly,Hippo kinases exclusion from the leading edge and being restricted in the cytosol is resulted from the MIG-2/RhoG activity.Taken together,our study propose a new mechanism that Hippo-RhoG signaling formed a negative feedback loop that maintains the polarity of migration cells.