Effect of Ptf1a misexpressed at E13.5 on the formation of different retinal cell types. (A) Schematics of control-GFP and Ptf1a-GFP retroviral constructs. The internal ribosomal entry site (IRES) allows for efficient expression of both Ptf1a and GFP. (B) Quantitation of GFP+ cells that become immunoreactive for various cell type-specific markers. Each histogram represents the mean ± SD for three retinas. More than 500 GFP+ cells were scored in each retina. (C-N) Sections from retinas infected with control-GFP or Ptf1a-GFP viruses were double-immunostained with an anti-GFP antibody and antibodies against the indicated cell type-specific markers. Forced Ptf1a expression in E13.5 retinas led to an increase in amacrine cells immunoreactive for Pax6, GLYT1 or GAD67 (C-H) and horizontal cells immunoreactive for Lim1 (I, J), but a decrease of ganglion cells immunoreactive for Brn3a or Brn3b (K-N). Arrows point to representative colocalized cells and insets show corresponding outlined regions at a higher magnification. Abbreviations: GCL, ganglion cell layer; ONL, outer nuclear layer. Scale bar: I-N, 39.7 μm; C-H, 34 μm.