Fig. 1

Activation of ERK1/2 in ventral spinal cord progenitor cells correlates with the time of OPC specification. a Schematic of medial floor plate (MFP), lateral floor plate (LFP) and neural domain organization over development of the spinal cord, dorsal on top in all figures. At E4-E4.5, Shh expression (blue line) is restricted to MFP cells while Nkx2.2 and Olig2 are expressed in the adjacent non overlapping p3 (red) and pMN (green) domains, respectively. Following LFP formation (E5-E5.5), i.e. activation of Shh expression in the former p3 domain, progenitor cells of the pMN domain up-regulate Nkx2.2 leading to formation of the p* domain populated by Olig2 and Nkx2.2 coexpressing progenitor cells (yellow). From E6, Nkx2.2/Olig2 coexpressing OPCs (yellow) migrate from the p* domain to progressively populate the entire spinal cord. PZ = progenitor zone, MZ = marginal zone. b-d Temporal profile of P-ERK1/2 (green) and Nkx2.2 (red) on transverse sections of chicken spinal cord. b’-d’: Double detection of P-ERK1/2 (green) and Nkx2.2 (red) viewed at higher magnification of the ventral progenitor zone. Note the progressive ventral to dorsal activation of ERK1/2 in the ventral progenitor zone (b"-d") and detection of the P-ERK1/2 signal in the dorsal-most Nkx2.2-expressing cells (p* domain) at E5.5-E6 and 6.5-E7 (brackets in c′ and d’). Scale bars = 50 μm