Fig. 4.

DSCAM promotes RGC axon outgrowth in vitro. (A, C, E, and G) Retinal explants from E14.5 WT (A, E, and G) and Dscam^del17 mutants (C) cultured for 24 h in collagen gels seeded with control, Dscam-expressing cells (A and C), Dscaml1-expressing cells (E), or 100–300 µm from clusters of control or Dscam-expressing cells (G). Explants were fixed and stained with antibodies against β-tubulin (red) or DSCAM (green). Dotted lines in G indicate the outlines of the cell clusters. Outgrowth was quantified in the area above the dashed line. (B, D, F, and H) Mean ± SEM axon outgrowth of presumptive ipsilateral (VT) and contralateral (DT) RGCs from WT (B, F, and H) and Dscam^del17/del17 (D) retinal explants in the presence of control, DSCAM-producing, or DSCAML1-producing cells. The number of explants analyzed is indicated on the bars. Data are the mean of at least four independent experiments analyzed blinded to genotype and condition. ns, not significant; *P < 0.05; **P < 0.01; ***P < 0.001. (Scale bars: 250 µm.)