Almost all mammals avoid eating chili peppers and other “hot” foods, because of the pain they induce. But not the tree shrew, according to a study publishing in the journal PLOS Biology. The researchers found that this close relative of primates is unaffected by the active ingredient in chili peppers due to a subtle mutation in the receptor that detects it. They speculate that this is an evolutionary adaptation to enable tree shrews to cope with a peppery plant that makes up part of their diet.
Capsaicinoids, including the capsaicin found in chili peppers, are chemicals that deter animals from eating them. They act by triggering the activation of TRPV1, an ion channel found on the surface of pain-sensitive cells in the tongue and elsewhere. TRPV1’s normal job is to alert animal to the presence of harmful heat, which is why capsaicinoids induce a sharp burning sensation. While humans may develop a tolerance and even a liking for capsaicinoids, most animals avoid feeding on plants that contain them.
The authors observed that Chinese tree shrews (Tupaia belangeri chinensis) actively fed on chili peppers, and, in contrast with mice, did not reduce their food intake as the concentration of capsaicin increased. They found that while the levels of TRPV1 in mice and tree shrews were similar, and both mammals were similarly responsive to other painful stimuli, the TRPV1 ion channel in the tree shrew was much less responsive to capsaicin. The authors then revealed the reason for this; TRPV1 proteins of mice and tree shrews differed by a single amino acid in the binding pocket for capsaicin, a mutation that the researchers found reduced the binding ability, and thus pain-inducing potential, of capsaicin in the tree shrew’s form of the protein.
While chili peppers themselves do not grow in the tree shrew’s environment, a plant that produces abundant capsaicinoids, Piper boehmeriaefolium, does, and is an important food source for the tree shrew. The ability to feed on this plant while most other species avoid it, the authors suggest, was potentially an important driver for the spread of the TRPV1 mutation through the tree shrew population over time.
“We propose that this mutation is an evolutionary adaptation that enabled the tree shrew to acquire tolerance for capsaicinoids, thus widening the range of its diet for better survival,” Han says.
The International Mouse Phenotyping Consortium (IMPC) has been predominantly interested in using mouse models to understand human health and disease. In a new study in the journal Conservation Genetics researchers have found another intriguing use of IMPC data.
By comparing genetic functional data from the IMPC with other non-human animals, it may be possible to identify genes relevant for the normal development in those species. For example, by comparing mouse genetic functional data with genomic data for selected species with specific diseases, improved breeding management could be implemented.
To test this potential application researchers at the European Bioinformatics Institute (EMBL-EBI) and Queen Mary University London (QMUL), alongside colleagues from the IMPC, compared genetic functional data from mice with genomic data from gorillas, showing how such analyses could aid in the identification of genes essential for healthy development.
As well as gorillas, the researchers highlighted other examples, including cheetahs, polar bears, wolves, pandas and cattle. This type of analysis could improve the current management approaches to breeding endangered species, by allowing researchers to identify the matches that are most likely to produce healthy offspring or select breeders to preserve genetic variation relevant for adaptation.
Heart disease is a common cause of death for gorillas in captivity and cheetahs suffer from impaired fertility both in captivity and in the wild. By identifying gorilla genes linked to heart disease or cheetah genes linked to infertility, researchers could help better understand the cause for the condition, which is the first step to envisage ways to prevent it. Similarly, this type of data could help identify genes linked to adaptation in certain mammals. For example, genes associated with fat metabolism can be a real asset for species like polar bears, which have diets rich in fats in the extreme environment of the Arctic.
“When the number of individuals of a species dramatically decreases, loss of genetic variation also takes place”, explains Violeta Muñoz-Fuentes, Biologist at EMBL-EBI. “This can result in many offspring not surviving, or exhibiting genetic defects linked to fertility or health problems.”
“Many zoos and wildlife conservation centres are seeing excellent results through their breeding programmes. Currently, many focus on minimising inbreeding. By adding a functional genetic dimension to the selective process, conservation geneticists can identify the crosses that would, for example, avoid a gene variant linked to disease in the offspring. It is nevertheless important to keep in mind that for a genetic rescue approach to be successful in the long term, the conditions that led to the decrease of individuals need to be removed; otherwise, the accumulation of deleterious alleles will likely take place again”.
Although this type of research is still in its early stages, gene functional knowledge is a powerful tool for maximising adaptive genetic diversity within a species and even for reducing genetic variants that negatively affect an individuals’ health and survival. With the accumulation of gene function annotation by the IMPC, as well as technical advancements in gene editing such as CRISPR/Cas9, the hope is that this method of comparing genome information between laboratory mice and endangered wildlife will help in future conservation projects.
The IMPC would like to encourage conservation geneticists, conservation centres and zoos to get in touch if they are interested in using IMPC data for conservation purposes.
Amalio Telenti discusses his recent article in Nature: Human gene essentiality
Link to article: https://www.nature.com/articles/nrg.2017.75.pdf
More information on this research can be found on Amalio’s website: https://www.stsiweb.org/about/faculty/telenti-amalio/
You can also follow Amalio on Twitter: https://twitter.com/atelentia