Like other membrane guanylyl cyclases, the 1101 aa retGC is predicted to have a hydrophobic amino-terminal signal sequence followed by a large extracelluiar domain, a single membrane spanning domain, a kinase homology domain, and a guanylyl cyclase catalytic domain. In contrast to other membrane guanylyl cylases, such as natriuretic peptide receptors, retGC has a relatively high basal level of activity when expressed in human 293 cells. cGMP production by retGC is unaffected by any of the known natriuretic peptides. In situ hybridization analysis of a variety of rhesus monkey tissues showed retGC transcripts to be localized exclusively along the retinal outer nuclear layer, corresponding to the nuclei of the rod and cone photoreceptor cells. Our results suggest that retGC may synthesize cGMP required for recovery of the dark state after phototransduction.
Selection B - Gene function is consistent with phenotype.
GOterm: GO:0007168 (receptor guanylyl cyclase signaling pathway)
FunctionalEvidence: Exogenous expression of the gene product in 293 cells exhibits a high level of cGMP production activity. When combined with the in situ hybridization evidence showing its expression along the retinal outer nuclear layer (coinciding with the rod and cone photoreceptor cell nuclei), this biochemical evidence indicates a function in synthesizing cGMP to promote recovery of the dark state following phototransduction.
FunctionalHPO: HP:0000662 (Nyctalopia), HP:0007663 (Reduced visual acuity), HP:0007688 (Undetectable light- and dark-adapted electroretinogram), HP:0007703 (Abnormality of retinal pigmentation)
PhenotypeEvidence: The ability of the exogenously expressed enzyme to efficiently catalyze cGMP production (Figure) is consistent with the loss of photoreceptor function that is characteristic of the disease, as abnormalities in cGMP levels have long been associated with photoreceptor degeneration (PMID: 4369896).