Alternative Splicing of the APC Gene in the Neural Retina and Retinal Pigment Epithelium

Abstract

Abstract: : Purpose:To test the hypothesis that differences in expression patterns of adenomatous polyposis coli (APC)tumor supressor protein are critical to RPE proliferation/differentiation. Methods:APC gene expression patterns were characterized in fetal and adult human and mouse retinas and RPE by RT-PCR and RNase protection analysis (RPA). APC protein isoforms were characterized by western blot analysis and immunocytochemistry. Results:RT-PCR or RPA demonstrated a predominant exon 1-containing, conventional APC splice-form in the developing RPE and retina or proliferative RPE cultures. These methods also demonstrated an increased level of exon 1-lacking APC splice-form in the mature RPE and retina or differentiated RPE cultures. Western blot analysis and immunofluorescence microscopy demonstrated the exon 1-lacking APC isoform in the retina and RPE, and the conventional APC only in the RPE. Immunofluorescence also demonstrated the co-existence of the conventional APC and exon 1-lacking APC isoforms in qquiescent, differentiated RPE cells, and only the conventional APC in proliferative RPE cells. Conclusion:These results suggest that alternative splicing of APC gene leads to differential APC expression with potential unique functions. Exon 1-lacking APC may play a role in cell cycle cessation in the adult retina and RPE, and the downregulation of this APC isoform may contribut to the potential of RPE to migrate and proliferate.

Keywords: 567 retinal pigment epithelium • 528 proteins encoded by disease genes • 417 gene/expression