December 20,
2018, Cell Press
Himalayan
marmots can survive at altitudes up to 5,000 meters in the Himalayan regions of
India, Nepal, and Pakistan and on the Qinghai-Tibetan Plateau of China, where
many of them face extreme cold, little oxygen, and few other resources. Now,
researchers have sequenced the first complete Himalayan marmot genome, which
may help them to better explain how the marmots live in such extremes.
The
findings, which appear December 20 in the journal iScience, hint at the
genetic mechanisms underlying high-altitude adaptation and hibernation, the
researchers say. They also serve as a valuable resource for researchers studying marmot evolution,
highland disease, and cold adaptation.
"As one
of the highest-altitude-dwelling mammals, the Himalayan marmot is chronically
exposed to cold temperature, hypoxia, and intense UV radiation," said Enqi
Liu of Xi'an Jiaotong University Health Science Center in China. "They
also hibernate for more than six months during the wintertime."
Those
striking biological features led Liu and his team, including first author Liang
Bai, to consider the Himalayan marmot as an ideal animal model for studying the
molecular mechanisms of adaptation to extreme environments. To begin, they
sequenced and assembled a complete draft genome of a male Himalayan marmot.
They also re-sequenced 20 other Himalayan marmots, including individuals living
at high and low altitudes, and four other marmot species. Additionally, RNA
sequencing was done to compare gene-expression differences between marmots in a
state of torpor and awake marmots.
The DNA data
show that the Himalayan marmot diverged from the Mongolian marmot about 2
million years ago. The researchers identified two genes, Slc25a14 and ψAamp (a
processed pseudogene), that have been selected in different directions in
marmots living at low versus high altitudes,
suggesting they are related to survival in high-altitude populations under
conditions of extremely low oxygen.
They further
suggest that Slc25a14 may have an important neuroprotective role. The shift in
ψAamp affects the stability of RNA encoding the gene Aamp, which may be a
protective strategy to prevent the excess growth of new blood vessels under
extremely low-oxygen conditions.
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