Position-dependent plasticity of primitive streak progenitors. ( A ) NMPs and LPMPs coexist in the caudal progenitor zone. The NSB and L1 regions show NM fate. NM potency is broader, encompassing L2–3 regions and coincides with a Sox2 + T + phenotype. LPMPs reside in the caudal-most embryo part; their potency to make PXM is somehow supressed. ( B ) Relative N vs M fate choices and trajectories for both progenitor populations are represented by directional purple and cyan arrows respectively, with length indicating proportions of cells entering each lineage. Background, relative expression of Sox2 (green) and T (red). Only NMPs require Wnt/β-catenin for mesoderm differentiation and maintenance. DOI: http://dx.doi.org/10.7554/eLife.10042.026