Immunofluorescence, BrdU labeling and cell counting
After fixation with 4% paraformaldehyde (PFA) in PBS for 15 minutes at RT, cells were
permeabilized and blocked with blocking solution (1×PBS containing 0.2% Triton X-100
and 3% BSA) for 1 hr. Primary antibodies in blocking solution were then added and
incubated overnight at 4°C, followed by washing and incubation with fluorophoreconjugated corresponding secondary antibodies. Proliferating cells were labeled by BrdU
(10 μM) for 2 hrs or throughout the culture, as indicated. BrdU-incorporation was detected
as previously described49. Briefly, PFA-fixed cells were treated with 2 M HCl for 30 min at
37°C, rinsed in 0.1 M boric acid for 10 min, and blocked with blocking solution. This was
followed by incubation with primary and secondary antibodies. The following antibodies were used: rabbit anti-NGN2 (Chemicon, 1:500), rabbit or mouse anti-Tuj1 (Covance,
1:20,000), mouse anti-MAP2 (Sigma, 1:750), chicken anti-Tau (AVES, 1:500), mouse antiNeuN (Chemicon, 1:500), mouse anti-vGluT1 (UC Davis, 1:100), mouse antisynaptotagmin 1 (SYT1, DSHB, 1:200), rabbit anti-GABA (Sigma, 1:2000), rabbit antiSox1 (Cell Signaling, 1:100), rabbit anti-Sox2 (Chemicon, 1:500), rabbit anti-Olig2
(Millipore, 1:500), mouse anti-BrdU (Sigma, 1:2000), mouse anti-HB9 (DSHB, 1:100),
mouse anti-ISL1/2 (DSHB, 1:100), mouse anti-VAChT (DSHB, 1:200), goat anti-ChAT
(Chemicon, 1:200), and Alexa Fluor-conjugated secondary antibodies made in donkey
(Invitrogen, 1:500). Images were obtained with a Carl Zeiss LSM510 Confocal Microscope
or an Olympus BX51 Microscope equipped with StereoInvestigator software (MBF
Bioscience). After counting the total number of Tuj1+ cells within the entire well of a 24- or
48-well plate in triplicate, conversion efficiency was calculated by normalizing to the
number of plated cells or to the number of surviving GFP+ cells.