Plexins B2 and B3 stimulate neurite outgrowth. (A) Examples of primary murine cerebellar neurons isolated from six days old c57BL/6J mice and grown on L1-, B2-, or B3- expressing transfected (L1, B2, B3) or non-transfected (3T3) NIH-3T3 substrate cells. (B) Mean length of neurites of murine cerebellar neurons grown for 24 h on NIH-3T3 substrate cells. Nontransfected substrate cells (3T3) served as negative control. Cells transfected with pIRES/L1 encoding neuronal cell surface molecule L1 (L1) served as positive control. The strongest stimulation of neurite outgrowth was observed on substrate cells transfected with pIRES/B3 encoding full-length plexin B3 (B3). Plexin B2-expressing substrate cells (B2) were transfected with expression construct pFLAG/B2. Each outgrowth assay was done in three independent experiments. Pooled data of the triple experiments are shown. A minimum of 400 neurons were analyzed for each substrate cell type. Error bars: S.E. of mean × 1. Mean neurite length differed significantly between all groups (ANOVA; **, p < 0.0005; *, p = 0.0033). (C) Culmulative size distribution patterns of the neurites given in B.