Fig. 2. Brn3a autoregulation increases with developmental age. The expression of ß-gal mRNA from the Brn3a/lacZ transgene was measured in embryonic tissues by RT-PCR. Autoradiograms and the corresponding phosphorimager integration of the triplicate assays are shown. (A) E12.5 head, representing ß-gal expression in the cranial sensory ganglia. (B) E13.5 head and (C) trunk, representing expression in the dorsal root ganglia. To confirm that Brn3a autoregulation is not dependent on the transgene insertion site, the relationship between ß-gal expression and gene dosage was examined for two independent reporter lines, which gave indistinguishable results. The ß-gal staining in Fig. 1B,C, and the quantitative assays in B represent the first of these lines, and the results shown in A,C are from the second line. Assays represent the mean±s.d. of triplicate PCR assays, and all determinations were repeated in at least three experiments. Phosphorimager units are arbitrarily scaled and cannot be compared between different sets of assays.