Fig. 4. A brief exposure to Erk1/2 signalling is sufficient to trigger neural specification. (A) Schematic of experiment. ES cells were differentiated for 2 days in N2B27+PD184352 before media was changed to N2B27±PD184352 for the specified time. Following this, the cells were lysed and analysed for activation of Erk1/2 (B) or media containing PD184352 was replaced and cells were cultured for 15 hours before FACS analysis (C). (B) Erk1/2 activation following inhibitor withdrawal at day 2. ES, ES cell lysate; -/+, cells differentiated for 2 days in constant absence/presence of PD184352. (C) Effect of different time periods of Erk1/2 activity on neural specification. y-axis marks the percentage increase of Sox1-EGFP-expressing cells following culture in the absence of PD184352 over culture for the same time in the presence of PD184352. Results are averages±s.e.m. from three experiments performed in triplicate.