Fig. 4. Effect of forced Barhl2 expression on retinal inner nuclear cells. (A) Schematic of control-GFP and Barhl2-GFP retroviral constructs. In Barhl2-GFP, a bicistronic transcript containing an internal ribosomal entry site (IRES) is produced from the viral LTR promoter, which allows efficient expression of both Barhl2 and the GFP marker protein. (B,C) Virus-transduced GFP⁺ (green) cells were visualized in P30 retinal sections that were weakly counterstained with nuclear DAPI. Infection with Barhl2-GFP viruses caused a significant increase of cells situated within the inner region of the inner nuclear layer. Arrows in C indicate two such cells. (D) Percentages of virus-transduced cells located in different cellular layers of the retina (means±s.d.). More than 600 GFP⁺ cells in three independent retinas were scored for either control-GFP or Barhl2-GFP virus. The inner nuclear layer was divided into the outer and inner halves for quantitation. GCL, ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; ONL, outer nuclear layer; OPL, outer plexiform layer. Scale bar: 10 µm.