Fig. 3. Loss of ß1 integrin does not impair neural stem cell self-renewal as assessed by neurosphere formation over several passages. (A) No difference was found in the percentage of X-gal-positive recombined neurospheres between mutants and controls at passages (P) 1, P2 and P4 in the presence of 10 ng/ml of EGF and 20 ng/ml of FGF-2. The absence of a significant genotype-specific reduction of recombined neurospheres over several passages suggests that ß1 integrins are not essential for maintenance of neural stem cells. (B) The percentage of X-gal-positive neurospheres also did not significantly vary when the spherogenic assay was carried out at 1, 5 and 10 ng/ml EGF. This confirms that the loss of ß1-integrin expression does not affect the capacity of neurosphere formation. Note that 0.1 ng/ml EGF was too low for both mutant and control cells to support the formation of neurospheres. Results are the mean±s.d. of four experiments in A and three experiments in B.