We cloned the guanylate cyclase activating proteins, GCAP1 and GCAP2,
from chicken retina and examined their expression in normal and predeg
enerate rd/rd chicken retina. Northern analyses show that the amounts
of the single transcripts encoding GCAP1 and GCAP2 are reduced to abou
t 70% of normal levels in rd/rd retina. Western analyses reveal that G
CAP2 levels appear normal in this retina, while GCAP1 levels are reduc
ed by more than 90%. The specific downregulation of GCAP1 in rd/rd ret
ina 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.