Fig. 1. Transgene expression controlled by a Brn3a sensory enhancer is strongly autoregulated. (A) Diagram of the mouse Brn3a locus and the structure of a Brn3a/lacZ transgene. (B) The Brn3a upstream flanking sequences target ß-galactosidase expression to the cranial sensory and dorsal root ganglia and their axons in an E13.5 Brn3a heterozygote embryo. (C) Enlargement of the cervical dorsal root ganglia of three littermate embryos with different Brn3a genotypes, stained under identical conditions, in which ß-gal activity is inversely proportional to Brn3a gene dosage.