Fig. 4. Shh::GFP ligand distribution during the emergence of ventral pattern. (A-F) Sections of 6- to 12-somite-stage mouse ventral neural tubes were analyzed at three developmental time points as determined by the appearance of distinct ventral cell types at the ventral midline (T1, p2; T2, pMN; T3, p3). (G) Schematic showing the changes in domain state across three distinct regions (R1-R3) of ventral neural tube. Each region represents a 9 µm x 9 µm square along the D-V axis with R3 beginning at the apical region of ventral midline cells. Red, p3; white, pMN; blue, p2. (H-J) Single confocal sections of ventral neural tube at the apical region (Shh::GFP ligand, green; nuclei, blue). (K,L) Quantitation of Shh::GFP ligand intensity (y-axis, average pixel intensity) at different time points and regions. Each time point represents four sections from three embryos. Significant differences from R3 are indicated by asterisks [P-values: T3(R3,R2), P<0.0298; T3(R2,R1), P<0.1275; T3(R1,R3), P<0.0125; R3(T3,T2), P<0.0417; R3(T2,T1), P<0.0775; R3(T3,T1), P<0.0458].