Immunohistochemical labeling of embryonic brain sections or dissociated neural cells was performed as described previously [65 (link),66 (link)]. The following primary antibodies were used: Chicken anti-GFP (Invitrogen), Rabbit anti-GFP (Invitrogen), mouse anti-β-III Tubulin (Phosphosolutions), rabbit anti-acetyl-α-tubulin (Cell Signaling), and mouse anti-β-tubulin (Upstate). Appropriate secondary antibodies conjugated with Alexa Fluor dyes (Invitrogen) were used to detect primary antibodies. Polymerized F-actins were detected by labeling with phalloidin-Alexa 568 (Invitrogen).