By E12.5, Cre activity from both the Nkx2.1-Cre and DlxI1/2b-Cre alleles removed Zfhx1b RNA expression in the expected patterns (Figures 1A-1C). As previously reported, the Nkx2-1 allele did not express Cre in the dorsal-most portion of the MGE, thus explaining the persistence of Zfhx1b in that location (Figure 1B). Of note, in the Nkx2.1-Cre; Zfhx1b conditional mutant brains, Zfhx1b RNA expression was not observed in the cells that appear to be migrating from the dorsal MGE into the mantle of the LGE, suggesting that the Zfhx1b+ cells in the mantle of the E12.5 LGE are likely to be MGE-derived cells (e.g. cortical and/or striatal interneurons) (X in Figure 1B). Also, note that DlxI1/2b-Cre leads to recombination in the SVZ and MZ of the LGE, MGE and CGE (white arrowhead, Figure 1C and data not shown).
