Fig. 2. Downregulation of Brn3a expression in Brn3b-null retinas and co-localization of Brn3a and Brn3b in heterozygous Brn3b^3a/+ retinas. (A-F) In situ hybridization using Brn3b, Brn3a 3'UTR and lacZ probes to show the expression patterns of Brn3b, Brn3a and Brn3a^ki mRNA in E11.5-15.5 retinas. (A) Expression of endogenous Brn3a in wild-type mice. (B) Brn3b expression in wild-type mice. (C) Reduced expression of Brn3a in Brn3b-null retinas. (D) Absence of Brn3b mRNA in Brn3b-null retinas. (E) Expression of endogenous Brn3a in Brn3b^3a/+ retinas. (F) Onset of Brn3a^ki expression at E11.5 and the expression of Brn3a^ki mRNA in the GCL and the NBL of Brn3b^3a/+ retinas. (G-I) Immunolabeling of Brn3b^3a/+ retinas at E11.5-15.5 with anti-Brn3a (red) and anti-Brn3b (green). (G) Detection of Brn3a protein in Brn3b^3a/+ retinas in the NBL and the GCL. (H) Brn3b expression in Brn3b^3a/+ retinas in the NBL and the GCL. (I) Complete overlap of Brn3a and Brn3b expression in cells in the NBL and the GCL. Insets show the enlarged view of the corresponding boxed regions and revealed overlap of Brn3b and Brn3a. NBL, neuroblast layer; GCL, ganglion cell layer; l, lens. Scale bar: 100 µm.