Genetics and environment combine to give everyone a unique sense of smell

Genetically identical mice develop different smell receptors in response to their environments

Researchers from the Wellcome Trust Sanger Institute and their collaborators have shown that receptors in the noses of mice exposed to certain smells during life are different to genetically similar mice that lived without those smells. Published today in eLife, the study found it is this combination of genetics and experience that gives each individual a unique sense of smell.

Our sense of smell comes from the olfactory organ in the nose, which is made up of sensory neurons containing receptors that can detect odours. There are about one thousand types of olfactory receptors in the nose, compared with only three types of visual receptors in the eye, and 49 types of taste receptors on the tongue. Of our senses, the olfactory system is the most complex, and combinations of signals from different olfactory receptors allow people to smell an enormously large repertoire of odours. However, how different people vary in their smelling abilities is not well understood.

To investigate the sense of smell the researchers used laboratory mice as a model, comparing the olfactory neurons from genetically identical animals that grew up in different environments. They also compared animals that grew up in the same environment but were genetically different.

The team used RNA sequencing to see which receptor genes were active. The researchers found that genetics controlled which receptors were present in the mice. Crucially however, they found that the environment that the individual had lived in had a significant effect on the number of cells able to identify each smell.

“It became clear that the role of genes, especially those that encode olfactory receptors in the genome, is very important in the construction of nasal tissue, but there was a very remarkable contribution of the environment, something that has not been previously described to this extent. We found the cellular and molecular construction of the olfactory tissue at a given moment is prepared not only by the organism’s genes but also by its life history.”

Professor Fabio Papes An author on the paper from the University of Campinas in Brazil

Olfactory neurons are formed throughout an individual’s lifetime, and the study showed the olfactory system adapted to the environment, leading to more cells capable of detecting scents to which there has been greater exposure. As a consequence, different individuals, even if genetically similar, may have completely different olfactory abilities. This could contribute to the individuality of the sense of smell, even in humans.

The knowledge that an individual’s history can affect the structure of olfactory tissue neurons may have implications for personalised medicine as different people’s sense organs could be constructed differently and respond in different ways. Studying olfactory neurons can also provide information about how the neurons in the brain are organised and function.

“The neurons in the olfactory system are highly connected to the neurons in the brain and studying these can help us understand neuronal development. We have shown that each individual has a very different combination of possible olfactory neurons, driven by genetics. In this study we also show that, with experience of different smells, these combinations of neurons change, so both genetics and environment interplay to give every individual a unique sense of smell.”

Dr Darren Logan The lead author on the study from the Wellcome Trust Sanger Institute

More information

Participating Centres:

• Wellcome Trust Sanger Institute, Wellcome Genome Campus, Cambridge, CB10 1SA, UK.
• Department of Genetics and Evolution, Institute of Biology, University of Campinas,Rua Monteiro Lobato, Campinas, SP 13083-862, Brazil.
• Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, 27710, USA.
• Monell Chemical Senses Center, Philadelphia, Pennsylvania, 19104, USA.
• Department of Neurobiology, Duke Institute for Brain Sciences, Duke University Medical Center, Durham, North Carolina, 27710, USA
• Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, USA

Funding:

This work was funded by Wellcome (Grant 098051), Fundação de Amparo à Pesquisa do Estado de São Paulo (Grant 09/00473-0 and 2015/50371-0 ) and the European Molecular Biology Organization.