21/28 December 2019 | New Scientist | 61are the only deer species to have been tamed
by humans and about half are domesticated.
On the Norwegian islands of Svalbard, males
of the smallest subspecies weigh no more
than 90 kilograms. In the forests of Finland,
a stag can tip the scales at 250 kilograms.
Wherever they live, reindeer face challenges
that would kill many other animals, including
severe cold, limited food in winter and
extremely prolonged periods of daylight and
darkness. In June this year, some of the genes
that allow them to overcome these problems
were revealed in the first results from the
Ruminant Genome Project. It compared
reindeer DNA with that of other animals that
chew the cud and identified mutations galore.
“We were surprised to find so many unique
gene variants related to reindeer’s adaptation
to the Arctic environment,” says Zhipeng Li at
the Chinese Academy of Agricultural Sciences.
“Many of the same genes are involved in
the same processes in reindeer as they are in
humans,” says Rasmus Heller at the University
of Copenhagen, Denmark, who was also part of
the project. Take the biological clock. Humans
and most other animals have daily rhythms of
activity and inactivity linked to light and dark,
driven by the circadian clock. Reindeer do too,
but they can override this. In the 24-hour
daylight of an Arctic summer, they forage
almost around the clock so they can put on
as much weight as possible. In the dark depths
of winter, their metabolic levels plummet and
they have only short bouts of activity that
don’t adhere to a 24-hour pattern.
They share this ability to break the rhythm
of the circadian clock with other polar animals,
including the emperor penguin and a type of
grouse called the rock ptarmigan. “If you are an
Arctic animal, you are faced with the weirdness
of the light conditions,” says Heller. “This is a
challenge for an animal that doesn’t have the
genetic background to cope with it. It would
mess with everything from hormone
secretions to physiology.” The ruminant
genome studies reveal what is going on in
reindeer. They have unique versions of genes
that drive circadian rhythms. In particular, this
means one key protein called Per2 is mutated,
so that another protein crucial for this regular
cycle can’t bind to it. “A vital part of their
biological clock malfunctions,” says Heller.A cure for jet lag?
The discovery of these gene variants in
reindeer could perhaps be exploited to help
humans overcome jet lag, which results from
having to readjust to the light/dark cycle in a
different time zone. Disruptions to circadian
rhythm are also thought to play a role in
mood disorders such as depression.
The biological mechanisms underpinning
how reindeer override their circadian rhythms
could provide insight into sleeplessness, too.
“There are specific gene variants involved in
insomnia, and we can compare these with thegenes from reindeer to further understand
how people’s circadian rhythm is affected,”
says Li.
Another impressive ability is the way both
male and female reindeer grow new antlers
every year. Aside from the placenta, deer
antlers are the only mammalian organs that
can be completely regenerated. A reindeer’s
headgear can contain up to 10 kilograms of
bone and blood vessels, and grows up to
2.5 centimetres a day. How do they achieve this?
Research published earlier this year provides
an answer. “The genes that get turned on
in cells destined to become antlers are also
turned on in cancer cells” says Yunzhi Peter
Yang, a tissue engineer at Stanford University
in California. “Tissue regeneration and
cancer growth are two sides of the same coin.”
Yet reindeer are five times less likely to get
cancer than other mammals because they
have evolved highly efficient tumour
suppression mechanisms that control the
otherwise dangerous cancer pathways. This
extraordinary ability makes them of great
interest to researchers looking for new
ways to prevent or treat cancer in humans.
Growing antlers also requires a lot
of calcium, and that presents another
challenge. To absorb calcium from food
in the gut, mammals need vitamin D, which
is made through the action of sunlight on
skin. “It is particularly important for reindeer
to maximise their calcium uptake and
vitamin D production, but this is challenging
in an environment where there is essentially
no sunlight for half the year,” says Heller.
The reindeer’s solution, the Ruminant
Genome Project found, is a souped-up system
for producing vitamin D that is far more
efficient than ours.
Understanding how reindeer antlers grow
might help us regenerate tissues in humans.
“Can we borrow the same mechanisms for
bone diseases such as osteoporosis or bone
cancer?” says Yang. “There is so much potential.”
Some of it has already been realised: the way
antlers are attached to the skull has inspired
the design of a new kind of bone-anchored
prosthesis for people missing limbs.
Flying and red noses are all very impressive
but it turns out that the real reindeer powers
are just as exciting – and, more importantly,
they’re not just for Christmas. ❚Alison George is a features
editor at New Scientist.
She loves writing about
big-eyed deersAcross the Taimyr peninsula
in Russia, races are held to
celebrate Reindeer-Breeder dayITAR-TASS^ NEWS^ AGENCY/ALAMYSTOCK^ PHOTO