Fig. 3. Targeted disruption of Isl1 results in the developmental loss of RGCs. (A-H) Immunostaining of retina sections with anti-BRN3B reveals a significant loss of BRN3B+ RGCs in Isl1 nulls at E17.5 (C,G) and E18.5 (D,H). Insets show the enlarged views of the central retina. (I,J) Anti-activated caspase3 immunostaining shows an increase in apoptotic cells (arrows) in the GCL of Isl1-null retina. (K) The difference of apoptotic cell numbers in wild-type and Isl1-null retina is insignificant at E13.5-15.5. However, in Isl1 nulls, the apoptotic cells are significantly increased from E16.5. Each histogram represents the mean+s.d. n=3 or 4 for each genotype per stage. ^*P<0.05, ^**P<0.01; t-test. R, retina; L, lens; NBL, neuroblast layer; GCL, ganglion cell layer. Scale bars: 100 µm in A-D; 25 µm in I.