Fig. 1. Gsx1/2 double mutants display a greater increase in OPC specification from dLGE progenitors than Gsx2 mutants.

At E15.5, control dLGE progenitors generate many Sp8- positve neuroblasts (C) and very few OPCs, as indicated by lack of PDGFRα expression (A) and only scattered Olig2 expression within the SVZ (B). Gsx2 mutants conversely express much lower levels of Sp8 (G) and instead ectopically express high levels of PDGFRα (E) and Olig2 (F) within the dLGE. This loss of Sp8 corresponds with the expanded OPCs, indicated in an overlay of Sp8 and Olig2 (H, compared to D). Gsx1/2 double mutants display even higher levels of PDGFRa (I) and Olig2 (J,L) expression within the dLGE. Accordingly, only a few cells express Sp8 within this region of double mutants (K,L). Quantification of these cells indicate that Gsx1/2 double mutants have significantly more PDGFRα expression within the VZ/SVZ and Olig2 expression within the SVZ than Gsx2 mutants, which have significantly more than control (Q,R). Correspondingly, Gsx1/2 double mutants have significantly fewer Sp8-positive cells within the dLGE SVZ than Gsx2 mutants, which have substantially fewer than control embryos (S). Gsx1 mutant embryos display no defects in oligodendroglial or neuronal specification, and resemble control embryos with no PDGFRα expression (M), very little Olig2 expression (N,P), and normal levels of Sp8 (Ο,Ρ) within the dLGE. Data represent the mean ±SEM. *p<0.01, as determined by a one-way ANOVA followed by a Tukey HSD post-hoc test. Scale bar: P = 100μΜ