The amount of cell death was observed by TUNEL and caspase labeling of the P21 WT (A, C) and P21 mutant (B, D) retinae. Both TUNEL and caspase 3 labels showed an abundance of cell death expression in the outer nuclear layer of the P21 mutant rat retinae in comparison to the WT (arrows; B, D). Graphs depict counts of cells positive for TUNEL (E) and caspase 3 (F) label in each of the retinal cell layers (n = 3 retinae for each sample). There were no significant differences in the number of TUNEL (+) cells at P10; however, there was a large statistically significant increase in the number of TUNEL (+) cells at P21 (p<0.005). No significant differences were noted in the WT and mutant INL and GCL at P10 and P21 using caspase 3. However, statistically significant increases in caspase 3-labeled cells were found in the ONL of the Mks3 mutant in comparison to WT at both P10 and P21. (*p<0.01 and **p<0.001 respectively). GCL, ganglion cell layer; INL, inner nuclear layer; ONL, outer nuclear layer; OS, outer segment. Scale bar: (A) 50 µm.