Reduced expression of Zic1 and Tbr1 in Olig1-/- brains. Coronal brain sections at forebrain level from E18.5 (a-d) Olig1+/- and (e-h) Olig1-/- embryos were subject to in situ hybridization with Olig1 riboprobe (a, e), Wnt10b riboprobe (b, f), Zic1 riboprobe (c, g), or immunostaining with anti-Tbr1 (d, h). The expression of Wnt10b was similar between Olig1+/- and Olig1-/- (b, f). The Zic1 expression level was significantly reduced in Olig1-/- thalamus compared to that in Olig1+/- (c, g). Expression of Tbr1 was also reduced in the cortex of Olig1-/- embryos (d, h).