Figure 1.

Mash1 and Ngns are expressed in complementary patterns in the embryonic telencephalon. (A) A new Ngn2 null allele was generated by replacing the sequence encoding the bHLH domain with the lacZ reporter (Ngn2^lacZKI). Schematic representation of the endogenous Ngn2 locus (top), Ngn2 targeting vector (middle), and recombined allele (bottom). Southern blot analysis of NotI–SpeI-digested ES cell genomic DNA with 5′ and 3′ external probes that recognize a common 20-kb wild-type band and 7.5- and 10.5-kb mutant bands, respectively. (B,C,E) Distribution of transcripts for Ngn1 (B), Ngn2 (C) and Mash1 (E) on frontal sections through the forebrain of E12.5 embryos. (D) X-gal staining of Ngn2^lacZKI heterozygous embryos at E12.5. Ngn1 and Ngn2 are expressed in proliferating progenitors of the dorsal telencephalon and dorsal thalamus in an almost completely overlapping fashion. Mash1 is expressed in a complementary manner with transcripts at high levels in the VZ of the ventral telencephalon and ventral thalamus.