Abstract
Cyclic nucleotide-gated (CNG) channels have been characterized as important factors involved in physiological processes including sensory reception for vision and olfaction. The possibility thus exists that a certain CNG channel functions in gustation as well. In the present study, we carried out reverse transcription-polymerase chain reaction and genomic DNA cloning and characterized a CNG channel (CNGgust) as a cyclic nucleotide-activated species expressed in rat tongue epithelial tissues where taste reception takes place. Several types of 5'-rapid amplification of cDNA ends clones of CNGgust cDNA were obtained with various 5'-terminal sequences. As the CNGgust gene was a single copy, the formation of such CNGgust variants should result from alternative splicing. The encoded protein was homologous to known vertebrate CNG channels with 50-80% similarities in amino acid sequence, and particularly homologous to bovine testis CNG channel and human cone CNG channel with 82% similarities. CNGgust was functional when expressed in human embryonic kidney cells, where it opened upon the addition of cGMP or cAMP. Immunohistochemical analysis using an antibody raised against a CNGgust peptide demonstrated the channel to be localized on the pore side of each taste bud in the circumvallate papillae, with no signal observed for degenerated taste buds after denervation of the glossopharyngeal nerve. All these results, together with the indication that cyclic nucleotides play a role gustatory signaling pathway(s), strongly suggest the involvement of CNGgust in taste signal transduction.
Highlights
Cyclic nucleotide-gated (CNG) channels have been characterized as important factors involved in physiological processes including sensory reception for vision and olfaction
A CNG Channel Expressed in Rat Tongue Epithelia—We first tried to obtain cDNA fragments encoding a CNG channel by RT-PCR with mRNA prepared from the epithelia of rat circumvallate papillae
Because no appreciable expression of CNGgust mRNA was observed by Northern blot analysis even using 10 g of poly(Aϩ) RNA extracted from rat tongue epithelial tissues, it was considered very difficult to obtain any positive cDNA clone from a conventional cDNA library
Summary
Cyclic nucleotide-gated (CNG) channels have been characterized as important factors involved in physiological processes including sensory reception for vision and olfaction. We carried out reverse transcription-polymerase chain reaction and genomic DNA cloning and characterized a CNG channel (CNGgust) as a cyclic nucleotide-activated species expressed in rat tongue epithelial tissues where taste reception takes place. Identification of the cDNA for CNG Channel Expressed in Rat Tongue Epithelia, Named CNGgust—To identify the cDNA corresponding to the RT-PCR fragment encoding the CNG channel named CNGgust, genomic DNA cloning and 5Ј-RACE were carried out.
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