Q. Zhang et al., CANINE ROD PHOTORECEPTOR CGMP-GATED CHANNEL PROTEIN ALPHA-SUBUNIT - STUDIES ON THE EXPRESSION OF THE GENE AND CHARACTERIZATION OF THE CDNA, Experimental Eye Research, 65(2), 1997, pp. 301-309
Rod photoreceptor cyclic GMP gated-channel protein is a key component
of the visual transduction cascade in the vertebrate retina, The prote
in is composed of at least two subunits (alpha and beta). Mutations in
the alpha-subunit (CNGC1) have been shown to cause retinitis pigmento
sa (RP) in humans. Several heterogeneous canine retinal diseases, whic
h are clinically similar to RP, are known collectively as progressive
retinal atrophy (PRA) and occur in dogs in a breed-specific manner. Fo
r the purpose of examining CNGC1 gene as a candidate for PRA, we repor
t here the characterization of canine CNGC1 cDNA, and examine the expr
ession of the gene in different tissues by northern analysis, reverse
transcription and polymerase chain reaction (RT-PCR), and retinal immu
nocytochemistry. The characterized canine CNGC1 cDNA sequence contains
2717 nucleotides which include 211 bp 5'-untranslated region and 430
bp 3'-untranslated region including the poly A tail. It is predicted t
o encode a protein containing 691 amino acids which include six putati
ve transmembrane domains, a pore loop and a cGMP binding domain as wel
l as one potential extracellular site for N-linked glycosylation. Over
the coding region, the canine CNGC1 shares 85-90% identity in the nuc
leotide sequence and 91-94% identity in the deduced amino acid sequenc
e with its homologues in other mammalian species. However, the homolog
y drops to only 71% and 78% of shared nucleotide and predicted amino a
cid sequences, respectively, when compared to the chicken CNGC1. Among
all the tissues examined the gene is expressed at a much higher level
in retina as a major transcript of 3.5 kb length. In addition, anothe
r minor transcript (9.8 kb) is consistently observed in the canine ret
inal RNA which may represent the canine homologue of the rod specific
beta-subunit of the cyclic nucleotide-gated channel protein, Transcrip
ts were detected only in retina by northern analysis but low level of
expression of CNGC1 was detected in liver, kidney, heart and brain by
RT-PCR, The expression of the CNGC1 protein was found to be localized
specifically to the photoreceptor outer segment by immunocytochemistry
. (C) 1997 Academic Press Limited.