Figure 7

Expression of guidance receptors on the axons of cingulate pioneering neurons. (A-F) Expression of DCC (A, B), Npn1 (C, D) and neurofilament (E, F) in coronal sections of E18 wildtype (A, C, E) and Nfib-deficient (B, D, F) brains. Axons from neurons in the cingulate cortex initiate callosal tract formation, and express the guidance receptor DCC. Expression was seen on axons from the cingulate cortex (Cing) in both the wildtype and Nfib null mutant (arrows in (A, B)). However, expression of Npn1, another guidance receptor localised to cingulate pioneering axons, was diminished in the knockout in comparison to littermate controls (arrowheads in (C, D)). The perforating pathway (PP), shown via expression of the axonal marker neurofilament in wildtype sections (arrow in (E)), appeared relatively normal in mice lacking Nfib (arrow in (F)). (G-I) The retrograde tracer True Blue was injected into the cingulate cortex of E17 wildtype embryos in utero. At E18, immunohistochemistry on coronal sections against NFIB (G) demonstrated that the retrograde tracer (H) and NFIB were co-localised in a population of callosally projecting neurons in the cingulate cortex (arrowheads in (I)). (J) At E16, levels of Npn1 mRNA were significantly lower in Nfib mutants than in littermate controls (*P < 0.05; t-test). RNA from three independent replicates for both wild type (WT) and Nfib mutants (Nfib knockout (KO)) was quantified. Error bars indicate standard error of the mean. IZ, intermediate zone. Scale bar: A-F 200 μm; G-I 30 μm.