Fig. 9. Model summarising how the Mil/S1P signal regulates the anterior migration of prechordal plate progenitors. The Mil/S1P signal primarily regulates the anterior migration of prechordal plate progenitors by modulating cell motility and polarisation through PI3K, a key effecter of Pdgf (Montero et al., 2003), and it mediates directionality together with the Pdgf pathway through an unknown mechanism. Furthermore, the Mil/S1P signal is seemingly able to modulate the coherence of cell migration independently of Wnt11 function, which is required for E-cadherin-dependent cell cohesion (Montero et al., 2005). However, it is still unknown whether Mil modulates cell cohesion/adhesion through E-cadherin. There is interdependency between parameters, at least between coherence and motility, as shown in Fig. 5. Arrows indicate regulation based on published and present results; dashed arrows indicate possible co-operation between the signalling cascades.