Other genes related to Notch-signaling were also identified in the array analysis, including the Id2 and Id4 helix-loop-helix and Sox6 HMG-box transcription factors (Table S1). Expression of Id4 was increased in the VZ of the Nkx2.1-Cre mutant; however, no change in expression was detected in the DlxI12b-Cre mutant (Figures S6M-S6O’ and S6KK-S6MM’); this implies that Id4 does not contribute to the interneuron phenotype. Id2 expression showed a subtle expression increase in the Nkx2.1-Cre mutant (not shown); like Id4, we did not find a change in its expression in the DlxI1/2b-Cre mutant (not shown). Sox6 expression was also increased based on the array and an increase was seen in both Nkx2.1-Cre and DlxI1/2b-Cre mutants by in situ hybridization at E12.5 (Table S1 and Figures S1F-S1F’ and data not shown), which became more pronounced at E13.5 and E15.5 (Figures 2J-L’ and 3G-I’). Of note, Sox6 represses MGE expression of Ascl1 (Mash1) (Azim et al., 2009), a basic-helix-loop-helix transcription factor whose expression is promoted by Notch-signaling.
