Fig. 4. Defects in laminar structure and cell specification in Ptf1a mutant retinas. (A-F) X-gal staining of retinal sections from E18.5 Ptf1a^Cre/+;R26R embryos (A) and Ptf1a^Cre/Cre;R26R embryos (B) counterstained with Fast Red. (C,E) Higher-magnification images of the areas in the solid and broken rectangles in A, respectively. (D,F) Higher-magnification images of the areas in the solid and broken rectangles in B, respectively. Arrows in E indicate representative developing horizontal cells and the bracket in E indicates normal location of maturing amacrine cells in the E18.5 retina. The bracket in F indicates lacZ-positive nerve fiber layer, which is thicker than the control lacZ-negative nerve fiber layer (indicated by the small bracket in E). (G-J) Hematoxylin and Eosinstained sections of wild-type and mutant retinas at E18.5. Higher-magnification pictures of G and H are shown in I and J, respectively. Arrowheads in H indicate a front-line of cells in the outer neuroblastic layer invading into the GCL. (K,L) Wild type and Ptf1a^Cre/Cre E18.5 retinal sections were immunostained with an anti-Brn3b antibody. Scale bars: in B, 100 µm for A,B; in H, 50 µm for E-H; in D, 25 µm for C,D; in L, 25 µm for K,L; in J, 10 µm for I,J. (M) Top, increased ganglion cell number in Ptf1a^Cre/Cre retinas. Bottom, no significant change in central retinal thickness in the mutant. Histograms represent the mean±s.d. of measurements from five animals of each genotype. ^*P<0.001. Abbreviations: GCL, ganglion cell layer; IPL, inner plexiform layer.