Control of Neural Stem Cells Figure 2. Hh pathway activation expands the population of cells with stem cell-like properties and promotes symmetric proliferative divisions of radial glial cells. (A) E14.5 Ptc1Lox/Lox;NestinCre neocortex (n = 10) showed an 8-fold increase (***p,0.0001) in the number of primary neurosphere colonies per cell seeded compared to littermate controls (n = 11). For RbpjLox/Lox;NestinCre and Ptc1Lox/Lox;RbpjLox/Lox; NestinCre samples, n = 3 and n = 4 respectively. * and ** p,0.005 by unpaired Student’s t-test (with Welch’s correction). (B) Clonal expansion of neurospheres derived from E14.5 neocortex. Cell numbers obtained at each passage were transformed into LOG and linear regression analysis was performed on resulting curves. The rate of clonal expansion of the neurospheres is represented as the slope of the line. The number of stem cells was significantly increased in Ptc1Lox/Lox;NestinCre neurospheres compared to Ptc1Lox/Lox neurospheres (slope: 0.887760.06774 vs 0.706060.03302, p,0.05). However, RbpjLox/Lox;NestinCre and Ptc1Lox/Lox;RbpjLox/Lox;NestinCre neurospheres showed a significant reduction in stem cells compared to the PLoS ONE | www.plosone.org 6 February 2011 | Volume 6 | Issue 2 | e14680