AsianScientist (Aug. 22, 2014) – Elephants’ noses are not only unusually long, but also provide them with an exceptional sense of smell. The ERATO Touhara Chemosensory Signal Project has shown that elephants have the largest number of olfactory receptor (OR) genes, more than twice those found in dogs and five times more than in humans.
The ability to distinguish different odors depends on the number and type of ORs found in an organism’s genome. Under the ERATO Touhara Chemosensory Signal Project, the research group of Prof. Yoshihito Niimura, Dr. Atsushi Matsui, and Prof. Kazushige Touhara from the University of Tokyo examined the OR genes encoded in 13 mammalian species’ genomes and found that African elephants have a surprisingly large number of OR genes, approximately 2,000 in total. Their results have been published in the journal Genome Research.
The authors went on to developed a novel bioinformatic tool to trace the evolutionary trajectories of individual OR genes, and examined their duplication and loss in each species. Some lineages of OR genes greatly expanded in a given species—such as an ancestral gene that has duplicated in elephants, generating 84 distinct genes—while other OR gene lineages were contracted in evolution.
They also discovered three unique olfactory receptor genes that are evolutionarily very stable, surviving 100 million years without any change in gene number and with very little change in sequence. This suggests that these receptors may have physiologically important functions common to every mammal beyond the detection of odors.
Each species’ unique OR repertoire has been shaped by hundreds of gene duplications and losses during evolution to adapt to each species’ living environment. Comparison among OR gene repertoires helps us to understand the molecular basis for differences in olfaction across organisms including humans.
The article can be found at: Niimura et al. (2014) Extreme Expansion of the Olfactory Receptor Gene Repertoire in African Elephants and Evolutionary Dynamics of Orthologous Gene Groups in 13 Placental Mammals.
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Source: University of Tokyo.
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