Fig. 6. The TrkA minimal enhancer containing both Brn3a-binding-site mutations has reduced activity in trigeminal ganglia. Representative trigeminal ganglia ß-galactosidase activity driven by the wild-type TrkA minimal enhancer (A,E), by a TrkA minimal enhancer bearing a 5' Brn3a-binding-site mutation (B,F), by a TrkA minimal enhancer bearing a 3' Brn3a-binding-site mutation (C,G), and by a TrkA minimal enhancer bearing both Brn3a-site mutations (D,H,I) at E13.5 and E17.5. Only the TrkA minimal enhancer with both mutations caused severe reduction in enhancer activity at E13.5 and E17.5.