Novel genes for potential ligand-binding proteins in subregions of the olfactory mucosa.

Odorant detection is specifically mediated via receptor neurons in the olfactory mucosa but is a complex process involving a number of different cell types producing proteins of differing function. We have used the technique of subtractive hybridization cDNA cloning to identify novel genes expressed exclusively in the olfactory mucosa which may play a role in olfaction. Ten distinct groups of cDNA clones were identified which corresponded to mRNA transcripts highly expressed in rat olfactory mucosa but undetectable in thymus, kidney, lung, brain, spleen and liver. Some of these clones identify substructures in the mucosal tissue for which no other probes are currently available. Others identify novel mRNA species in the Bowman's glands. The predicted proteins for three of these clones are homologous to proteins which bind to either lipopolysaccharides (RYA3 and RY2G5) or to polychlorinated biphenyls (RYD5). In addition, while RYA3 and RY2G5 are highly homologous, they appear to be expressed in different parts of the mucosal tissue. The sequence homologies and subanatomical location of expression suggest that these proteins might interact with odorants before or after specific recognition by odorant receptors. Therefore, the olfactory mucosa may possess diverse, functionally-distinct odorant-binding proteins which recognize and bind separate classes of odorants.