Fig. 5. The capacity to maintain nestin-positive progenitors within individual neurospheres is modulated by ß1-integrin expression. (A) The presence of at least one nestin-positive cell was assessed for each plated ß1-deficient neurosphere after 6 days of differentiation in the absence or in the presence of growth factors. In the absence of exogenous growth factors, the number of clones containing at least one nestin-positive cell is significantly decreased (***P<0.001) compared with control clones on laminin-1 (LM1), fibronectin (FN) or PDL substrates. By contrast, 85-95% of the mutant clones cultured in limiting growth factor conditions (3.3 ng/ml EGF, 2.0 ng/ml FGF, 10 ng/ml NGF) contained at least one nestin-positive progenitor cell. Results are the means±s.d. of three separate experiments. (B-C) Representative pictures of clones derived from control neurospheres (B) and from mutant neurospheres (C), cultured in the absence of growth factors for 6 days, and stained for nestin (red) and DAPI (blue). Bar, 70 µm.