Examining the source behind Sherpa mountain fitness

Sep. 18, 2013 — The Sherpa population in Tibet is world-renowned for their extraordinary high-altitude fitness, as most famously demonstrated by Tenzing Norgay's ability to conquer Mount Everest alongside Sir Edmund Hillary. The genetic adaptation behind this fitness has been a topic of hot debate in human evolution, with recent full genome sequencing efforts completed to look for candidate genes necessary for low oxygen adaptation. However, few have looked at the Sherpa population by sequencing their mitochondrial genomes -- the powerhouse of every cell that helps determine the degree of respiratory fitness by providing 90 percent of the human body's energy demand, as well as controlling the metabolic rate and use of oxygen.

Unlike genomic DNA, the mitochondrial genome is unique inherited only through the mother, is small in size, and has a high mutation rate. Researchers Longli Kang, Li Jin et al. have sequenced 76 Sherpa individuals' complete mitochondrial genomes living in Zhangmu Town, Tibet, and found two mutations that were specific to the Sherpa population. The authors suggest that variants for one recent mutation in particular that was introduced into the Sherpa population about 1,500 years ago, A4e3a, that may be an important adaptation for low oxygen environments, or hypoxic conditions. This mutation is found in an "entry enzyme" stage in the mitochondrial respiratory complex, which may explain the importance of the role of mitochondria in the Sherpa population's ability to adapt to the extreme Himalayan environment.

The authors also shed light on the demographic history of Sherpa population size over evolutionary time, showing a significant expansion from 3,000 to 23,000 around 50,000 years ago, followed by a very recent bottleneck in the past several hundred years that reduced the population from 10,000 to 2,400, matching known historical migration patterns.

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Story Source:

The above story is based on materials provided by Molecular Biology and Evolution, via EurekAlert!, a service of AAAS.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

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Journal Reference:

1. L. Kang, H.-X. Zheng, F. Chen, S. Yan, K. Liu, Z. Qin, L. Liu, Z. Zhao, L. Li, X. Wang, Y. He, L. Jin. MtDNA lineage expansions in Sherpa population suggest adaptive evolution in Tibetan highlands. Molecular Biology and Evolution, 2013; DOI: 10.1093/molbev/mst147

Note: If no author is given, the source is cited instead.

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Livestock 'not salmonella source'

12 September 2013 Last updated at 18:13 GMT The researchers examined samples from people and animals infected with a specific type of Salmonella Livestock may have been wrongly blamed as being the source of a type of drug-resistant salmonella, a study shows.

UK researchers examined the DNA from 373 humans and animals infected with a specific type of salmonella collected by a Scottish lab over 22 years.

Writing in Science, they say the genetic profiles of the infections in humans and animals were very different.

An epidemic of this strain - Salmonella typhimurium DT104 was seen in animals and humans in the 1990s.

More than 94 million people globally develop food poisoning or gastroenteritis each year after being infected with all types of salmonella.

Drug resistance makes treatments ineffective, causing more complex illness and increased treatment costs.

It had been suggested that such resistance could spread from animals to people via the food chain or through animal waste contaminating the water supply.

'Great surprise'

The team, from the Wellcome Trust Sanger Institute, sequenced DNA from people and animals infected with Salmonella typhimurium DT104.

They looked very different, and the human samples were much more complex than those seen in animals - which would have been the reverse had livestock been the source.

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Discovering that the animal and human populations of salmonella were as distinguishable as they were was a great surprise to us”

End Quote Prof Stuart Reid, Royal Veterinary College Prof Nick Thomson, senior author on the study, said: "Our data provide a very simple message, challenging the established view that local animals are the predominant source of salmonella infections in Scotland.

"This finding will reinvigorate discussions on the sources of antibiotic resistant salmonella infections in humans in other environments."

Prof Stuart Reid from the Royal Veterinary College, who also worked on the study, said: "Discovering that the animal and human populations of salmonella were as distinguishable as they were was a great surprise to us."

And he said the research showed "greater efforts" were needed to identify the major sources of resistance for animals and people.

Writing in the same journal, Dr Mark Woodhouse and Dr Melissa Ward from the University of Edinburgh's Centre for Immunology, Infection and Immunity said: "The results suggest that the human and livestock epidemics were largely independent, though with some jumps in both directions between the two populations."

They suggest the drug-resistant strains could have been introduced via imported food products, but say much more research to pin down the actual source is needed.

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