Early patterning of the cKO forebrain. (a-f') WMISH and (g, g') ISH on sections. Shh (a, a') and Fgf8 expression (e, e') at E9.5 is unchanged in cKO. The septum and large parts of the MGE anlage (red and white arrowheads in (b, b')) are free of Nkx2.1 activity. Pax6 activity is diminished in cKO (c, c'). Emx2 is slightly up-regulated in mutants (d, d'). At E10.5, Fgf8 is expressed in the telencephalic midline and septum anlage in both genotypes (f, f'). At E12.5, Fgf8 mRNA is specifically lost in the septum (red arrow in (g, g')). The Fgf8 positive domain in cKO at E12.5 matches the midline of the POA (black arrow in (g')).