Abnormalities of the retinal pigment epithelium in transgenic mice with APC gene modification

Purpose. Mutations in the human adenomatous polyposis coli (APC) gene result in the adenomatous polyposis syndromes, as well as congenital hypertrophy and hamartomas of the RPE. Transgenic mice, heterozygous for APC gene modification (chain termination mutation in the 15th exon), develop intestinal tumors similar to the human polyposis syndromes. We have examined eyes from APC-modified transgenic mice in order to determine if RPE abnormalities recapitulated the human counterpart. Methods. Eight eyes from four transgenic mice were immersion-fixed and processed for routine histology. Serial two μm sections were examined by light microscopy. Results. All of the eyes examined were characterized, predominantly, by regions of normal histology. In one eye, there was a reduplication of the RPE layer which directly abutted the RPE layer. In an adjacent region, RPE formed a separate layer of cells which was present between photoreceptor outer and inner segments. In another eye, an ectopic layer of RPE was found within the neural retina. In both eyes, there was evidence of photoreceptor cell degeneration underlying the aberrant RPE. Conclusions. Our findings indicate that the APC gene is important for regulation of RPE growth and suggest that this transgenic mouse line may provide insight into the APC gene/RPE relationship.