Sensory axon guidance in TrkC neurotrophin receptor-deficient mouse embryos. Mice carrying the 11 kb/LacZ transgene were interbred with TrkC^+/− mice, and then the resulting 11 kb/LacZ, TrkC^+/− mice were crossed with TrkC^+/− mice to produce litters containing the 11 kb/LacZ, TrkC^+/− embryos (A, C) and 11 kb/LacZ, TrkC^−/− (B, D) littermates. Examined at E13.5, TrkC mutant embryos lack the ectopic trigeminal branches noted in Brn3a null mice (A,B) and show normal encirclement of the whisker follicles by β-gal-expressing sensory axons (C,D). 5g, Trigeminal ganglion;Mn, mandibular division, trigeminal nerve;Mx, maxillary division, trigeminal nerve;Op, ophthalmic division, trigeminal nerve;Pr5, principal trigeminal nucleus.