Fig. 3.

Transcription of neuronal genes in the absence of NEX. A, Northern blot analysis of total brain RNA isolated at postnatal day 10 from wild-type (+/+) and from heterozygous (+/−) and homozygous (−/−) NEX mutant mice. Homozygous mutants show no major difference in the steady-state level of two marker genes for neuronal differentiation, synaptophysin (Syn) andGAP-43. With a neomycin-specific probe (neo), two mRNAs of 2.8 and 2.4 kb were detected in heterozygous and homozygous brains. Transcription of these mRNAs is initiated at the endogenous NEX promoter (compare with Fig.1A). NeuroD andNDRF mRNAs show little change in abundance. Cyclophilin (cyc) was used as an internal standard of RNA loading (5 μg/lane). B, In situ hybridization of horizontal brain sections from wild-type (+/+) and from homozygous (−/−) NEX mutant mice obtained at postnatal day 5 (c,d) and postnatal day 10 (a,b, e, f). Sections were hybridized with a neomycin-specific probe (neo;a, b), revealing NEX promoter activity, and with probes for GAP-43 (c,d) and NDRF (e,f). Note that the neomycin-specific probe shows the same overall expression pattern as a NEX-specific probe (see Fig.7A to compare), revealing the apparently normal differentiation of neurons that lack NEX. Distribution ofGAP-43 and NDRF mRNAs appears unaltered in NEX−/− mice.