Expression and cellular distribution of the al gap junction gene product in the ocular pigmented ciliary epithelium

The expression of four different gap junction (GJ) transcripts, corresponding to the alpha 1, alpha 3, beta 1 and beta 2 gene products, has been examined in the ciliary epithelium of human and bovine eyes, and in cultures of ciliary epithelial cells. Northern blot analysis revealed that alpha 1 mRNA, 3.6-kb in size, was the predominant transcript expressed in intact tissue and in cultures of pigmented ciliary epithelial cells (PE). No transcripts from the alpha 3, beta 1 or beta 2 gap junction genes were detected in intact tissue or ciliary epithelial cells as demonstrated by Northern blotting. When the levels of alpha 1 gap junction mRNA were compared between PE and NPE in primary cultures, a striking difference was observed in the level of alpha 1 transcripts: there was about a 6 to 8-fold increase in alpha 1 levels in PE cells, relative to the NPE cells. To verify the differential level of expression of alpha 1 GJ mRNA in the two cell types, indirect immunofluorescence localization studies were performed on semithin cryostat sections of ciliary processes. These studies revealed that alpha 1 gap junctions are present at the apical and lateral borders of PE cells, i.e. at the apical plasma membranes domains of PE-NPE cells, and at the lateral plasma membrane regions of PE-PE cells borders. Further analysis by immunoblotting confirmed that the 43 kD alpha 1 gap junction protein was the major gap junction gene product in the ciliary epithelium.