Olfactory receptors in aquatic and terrestrial vertebrates |
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Authors: | J Freitag G Ludwig I Andreini P Rössler H Breer |
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Institution: | (1) University Stuttgart-Hohenheim, Institute of Physiology, Garbenstrasse 30, D-70593 Stuttgart, Germany e-mail: physioll@uni-hohenheim.de Tel.: +49-711-459-2266; Fax: +49-711-459-3726, DE |
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Abstract: | In species representing different levels of vertebrate evolution, olfactory receptor genes have been identified by molecular
cloning techniques. Comparing the deduced amino-acid sequences revealed that the olfactory receptor gene family of Rana esculenta resembles that of Xenopus laevis, indicating that amphibians in general may comprise two classes of olfactory receptors. Whereas teleost fish, including the
goldfish Carassius auratus, possess only class I receptors, the `living fossil' Latimeria chalumnae is endowed with both receptor classes; interestingly, most of the class II genes turned out to be pseudogenes. Exploring
receptor genes in aquatic mammals led to the discovery of a large array of only class II receptor genes in the dolphin Stenella Coeruleoalba; however, all of these genes were found to be non-functional pseudogenes. These results support the notion that class I receptors
may be specialized for detecting water-soluble odorants and class II receptors for recognizing volatile odorants. Comparing
the structural features of both receptor classes from various species revealed that they differ mainly in their extracellular
loop 3, which may contribute to ligand specificity. Comparing the number and diversity of olfactory receptor genes in different
species provides insight into the origin and the evolution of this unique gene family.
Accepted: 29 July 1998 |
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Keywords: | Olfactory receptors Multigene families Pseudogenes Vertebrate species Evolution |
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