13 September 2012
Written by Darren Logan
Have you ever considered whether we all sense the world the same way? My lab at the Sanger Institute studies how our genes influence how we perceive the environment around us, and how our brains makes sense of our senses.
When it comes to studying sensory genes, the nose is a veritable goldmine. We have many hundreds of genes that each encodes a unique chemical receptor. It is these receptors, found only in the nerves of our nose, which capture the rich blend of chemical odorants that diffuse up from our morning coffee. When an odorant is the right shape to slot into its matching receptor, much like a lock and key, a signal is transmitted along that nerve to the brain. It is the combination of these many signals that our brains interpret as that rich coffee flavour.
Some animals, like mice or dogs, are super-smellers and have over one thousand of these receptor genes. They use some of the additional ones to detect special types of body odours, called pheromones. Since mice can’t talk and do most of their socializing in the dark of night, they use pheromones to identify and communicate with each other: social networking with smells, if you like.
Inquisitive young male mice are very attracted to the pheromones of a receptive female, for example, but avoid those from a dominant male. Because we can easily observe the natural behaviour of mice in response to pheromones, they make a great model for studying the receptors and the genes that encode them.
Just like humans, not all mice behave the same way. Some strains are more aggressive and others tame, some are much better at mating and others are superior parents. My lab wanted to know whether differences in their pheromone receptor genes might be a reason for these behavioural differences. After all, if a mouse does not interpret a social signal properly, it will not be able to respond correctly.
We searched for copies of these receptors in the genomes of 17 different strains of mice, comparing over 6000 genes in total. We found that they were unusually variable, over two times more than the average gene. All strains were completely lacking some receptors and a few had gained extra ones. No two strains were alike. Though among this diversity there were a few receptor genes that seemed to be particularly important, as they were completely unchanged in almost all strains. We think these may perceive critical social signals necessary for survival and are now working to find out exactly what behaviours they influence.
We recently published this work in BMC Genomics and we think the implications are rather remarkable: each mouse clearly has a very different capacity to perceive social signals. Like mice, do you and I also perceive smells differently? While we were studying mouse receptors, some colleagues in Israel were looking into human odorant receptor genes. The results were very similar: they report that (unless we are related) our receptor inventories probably differ by a third. So as Juliet told Romeo, “A rose by any other name would smell as sweet.” But we now know a rose, by any other nose, does not.
Elizabeth H Wynn, Gabriela Sánchez-Andrade, Keren J Carss and Darren W Logan ‘Genomic variation in the vomeronasal receptor gene repertoires of inbred mice’