Figure 1

Pan-sensory expression of Brn3a and survival of a majority of trigeminal neurons in Brn3a knockout mice. (A-E) Co-localization of Brn3a with specific sensory markers in the TG in transverse sections of P0 wild-type ganglia. Brn3a is co-localized with the pan-sensory marker Islet1 and the subtype-specific markers TrkA, TrkB, TrkC, and Ret. (F-I) Islet1 expression and LacZ expressed from the Brn3a locus (Brn3a^tLacZallele) were used to assess TG morphology and marker expression at E13.5. Ganglion morphology is grossly normal (F, G), and Islet1 continues to be expressed in LacZ⁺ neurons in Brn3a knockout embryos (H). No significant difference in the volumes of Brn3a^tLacZ/- and Brn3a^tLacZ/+ control TG was observed at this stage (I). The zero coordinate is the rostral pole of the ganglion. Paired T test for comparison of coronal section areas across the rostrocaudal extent of the ganglion: n = 8, P = 0.12, not significant. (J-L) At P0.5 Islet1 expression continued to identify all or nearly all LacZ⁺ neurons in Brn3a^tLacZ/- knockout and Brn3a^tLacZ/+ control TG (J, K, transverse section). Islet1 immunoreactive nuclei were counted in serial sections across the rostrocaudal extent of the TG (L), and mean cell number was reduced from 696 to 501 nuclei per section (72% remaining), with cell loss concentrated in the rostral pole of the ganglion. Paired T-test for comparison cell number in matched coronal sections across the entire rostrocaudal extent of the ganglion: n = 12, P = 0.01. 5 g, trigeminal ganglion; 9 g, geniculate ganglion; Di, diencephalon; Hb, hindbrain; HT, heterozygote control; KO, knockout; Ot, otic region.