Polarization of the C-elegans embryo by RhoGAP-mediated exclusion of PAR-6 from cell contacts

Early embryos of some metazoans polarize radially to facilitate critical patterning events such as gastrulation and asymmetric cell division; however, little is known about how radial polarity is established. Early embryos of Caenorhabditis elegans polarize radially when cell contacts restrict the polarity protein PAR- 6 to contact- free cell surfaces, where PAR- 6 regulates gastrulation movements. We have identified a Rho guanosine triphosphatase activating protein ( RhoGAP), PAC- 1, which mediates C. elegans radial polarity and gastrulation by excluding PAR- 6 from contacted cell surfaces. We show that PAC- 1 is recruited to cell contacts, and we suggest that PAC- 1 controls radial polarity by restricting active CDC- 42 to contact- free surfaces, where CDC- 42 binds and recruits PAR- 6. Thus, PAC- 1 provides a dynamic molecular link between cell contacts and PAR proteins that polarizes embryos radially.