Figure 7. A model for the roles of PCP and Nodal signaling in C and E gastrulation movements.

In intact embryos (left), Nodal signaling acts largely in parallel with PCP signaling to regulate the ML cell polarization that underlies C and E. PCP signaling activity and localization of its components are regulated by an additional unknown signal(s) (X), and maintains residual polarizing activity in the absence of Nodal. In embryonic explants (right), PCP signaling activity and C and E cell behaviors are regulated wholly downstream of Nodal signaling.