Responses of EGL cells to SDF-1. (a) Co-culture of an E17 EGL explant with control HEK cells. Scale bar, 100 μm. (b) Co-culture of an E17 EGL explant with HEK cells expressing SDF-1. (c) A higher-magnification view of the distal side of the explant shown in (b). (d) A higher-magnification view of the proximal side of the explant shown in (b). (e) Nuclear staining of the explants shown in (a). Green, staining with Hoechst 33258 dye. (f) Nuclear staining of the explants shown in (b). (g) Statistical analysis of EGL responses. The P/D ratio for control HEK cells differed significantly from that for SDF-1 cells (P < 0.0001, Mann-Whitney U-test), but not from that for RANTES cells (P > 0.5). (h–j) Co-culture of embryonic EGL explants with a control block (h), a collagen block containing recombinant SDF-1 (i) or a collagen block containing BDNF (j). SDF-1 (0.04 μM) was sufficient to attract embryonic EGL cells. BDNF did not attract EGL cells even at a concentration of 1.5 μM. (k–m) Co-culture of postnatal explants with a control block (k), a collagen block containing recombinant SDF-1 (l) or a collagen block containing BDNF (m). Postnatal EGL cells were not attracted or repelled by SDF-1 at concentrations as high as 1.0 μM. (n) Statistical analysis of EGL responses toward protein-containing collagen blocks. The P/D ratio for eEGL + SDF-1 differed significantly from that for eEGL + control (P < 0.01, Mann-Whitney U-test), whereas other comparisons did not show a significant difference from the controls (P = 1.000 for eEGL + BDNF, P = 0.107 for pEGL + SDF-1, P = 0.572 for pEGL + BDNF). The latter two were compared to pEGL + control. See Supplementary Methods online for details of these experiments.