Expression of GCAP1 and GCAP2 in the retinal degeneration (rd) mutant chicken retina.

We cloned the guanylate cyclase activating proteins, GCAP1 and GCAP2, from chicken retina and examined their expression in normal and predegenerate rdlrd chicken retina. Northern analyses show that the amounts of the single transcripts encoding GCAP1 and GCAP2 are reduced to about 70% of normal levels in rdlrd retina. Western analyses reveal that GCAP2 levels appear normal in this retina, while GCAP1 levels are reduced by more than 90%. The specific downregulation of GCAP1 in rdlrd retina is consistent with a model for this disease in which activation of guanylate cyclase in the photoreceptors is abnormal, resulting in low levels of cGMP and an absence of phototransduction.