FIG. 4.

Conditional Rb mutants display a defective migratory response to netrin-1. (A) Control (Foxg1-Cre/+; Rb^loxP/+) and conditional Rb mutant (Foxg1-Cre/+; Rb^loxP/loxP) MGE explants were cultured in collagen in the absence or presence of recombinant netrin-1. Migration was quantified by counting the individual cell bodies migrating from each explant. Bars in the graph at left represent the mean of the average number of cells migrating from an individual explant ± standard error of the mean. While control cells exhibit a nearly 4-fold increase in migration in the presence of netrin, no difference was observed in conditional Rb mutants between the presence and absence of netrin. Significance was determined through a paired two-tailed t test for explants of the same genotype and a two-tailed t test for explants of different genotypes. *, P < 0.05 (n = 4 embryos per treatment, per genotype; two to three explants were examined per embryo). (B and C) Cells from the ganglionic eminence of control and conditional Rb mutants were dissected and cultured as single-cell preparations in the presence or absence of netrin-1. Quantification of the proportion of cells in S phase (BrdU) or dying (Hoechst) reveals no change upon addition of netrin-1 in either genotype. Three separate embryos were analyzed in quadruplicate for both the control and conditional Rb mutant.