Figure 4.

Functional analysis of Alcam homophilic and trans-heterophilic interactions in the promotion of axon growth by an Alcam substrate. Representative TH⁺ axonal traces from primary ventral midbrain cultures of WT (A) or Alcam^−/− (B) neurons cultured on control or Alcam substrate. Quantification of axon growth in the presence of an Alcam substrate resulted in a significant increase in neurite length (C) (two-way ANOVA, Alcam substrate, F_(1,12) = 23.05, p = 0.004, n = 4) in both WT (t = 3.741, df = 12, p = 0.0056) and Alcam^−/− neurons (t = 3.049, df = 12, p = 0.0201), where loss of Alcam function on growing axons prevents homophilic interactions. A significant effect on branch number (D) (two-way ANOVA, substrate, F_(1,12) = 5.554, p = 0.0363, n = 4) was not significant in post hoc tests. Scale bars in A and B, 20 μm. Data are shown as mean ± SEM. *p < 0.05, **p < 0.01.