Fig. 1. Increased OP cell migration in the optic nerve of TN-C-null mice. (A) Schematic representation illustrating how optic nerves were serially sectioned for 1.8 mm from the retinal end towards the chiasm, and analysed in six adjacent segments (1 to 6) of 300 µm each by counting PDGFR mRNA-positive cells in 15 µm sections. The average cell number per section in each optic nerve segment is expressed as mean±s.e.m. The semi-quantitative method allowed us to compare the number of OP cells in each optic nerve segment in the wild-type and TN-C-null mice. Six mice at P0-P12 and four adult mice of each genotype were analysed. Note that at early stages of postnatal development (P0 and P2), more PDGFR mRNA-positive cells were found in each segment of the optic nerves from TN-C-null mice when compared with wild-type mice (Student’s t test: **P<0.01, ***P<0.001). At later stages (P5 to adult), no differences between genotypes were found. (B-E) Examples of in situ hybridisation experiments for PDGFR mRNA on optic nerve sections obtained from the sixth segment (A, arrow) are shown for wild-type mice (B,D) or TN-C-null mice (C,E) at P0 (B,C) and P5 (D,E). Note the increased number of cells in the P0 TN-C-deficient nerve. Scale bar: 100 µm.