Tucked away in a laboratory in the University’s medical
center, there lives a tiny creature whose sole existence has caused
celebration and anticipation within the scientific community. This
tiny creature is a dwarf mouse, and his name is Yoda.

Laura Wong
Yoda, left, sniffs cage mate Princess Leia. (COURTESY OF RICHARD MILLER, Medical School)

Though not on a calorie-restricted diet like other elderly mice,
Yoda is the world’s oldest known living mouse, turning four
last Saturday — approximately 136 in mouse years.

Weighing about one-third the size of a normal mouse and aging
much more slowly, dwarf mice are ideal for aging research because
like small dogs, they tend to live longer than their larger

Richard Miller, associate director of Research for the
University’s Geriatrics Center, said his goal is to develop a
comparison between the genes and hormone levels of slow-aging mice,
like Yoda, and those of other mammals. The key is to understand
which chemicals change in the body as aging occurs and eventually
to delay the effects of aging.

Despite Unit for Lab Animal Medicine office assistant Liz
Sherbert’s claim that “he has big, bushy eyebrows and
walks with a cane,” Yoda has not suffered the traditional
adverse effects of aging. His fur is a bit tattered, but he is
primarily free of disease and other age-induced ailments like
arthritis, cataracts and cancer.

Dwarves’ considerable lifespans allow researchers to map
out the aging process carefully and understand what chemicals
change in the body as the animals age. Miller has been working on
breeding mice that age more slowly than mice typically used in
aging research, and Yoda is part of this stock.

Dwarf mice are small because their genetic code contains a
dwarfing mutation that inhibits secretion of the thyroid hormone,
which is responsible for growth in mice, humans and other

Yoda is an example of how the dwarfing mutation has slowed down
aging and kept him relatively healthy for his age, Miller said.

“Yoda’s case is pretty rare,” said Howard
Rush, director of ULAM. “We don’t normally see mice
live this long.”

Miller’s research also focuses on the consequences of
aging on immunity.

An experiment like Yoda provides insight into what chemicals in
the body are responsible for aging.

“Yoda gives us evidence that hormone therapy may influence
aging,” Miller said. Researchers like Miller speculate that
hormone shots may influence aging, and research like that done on
Yoda could verify this hypothesis.

Yoda’s cage mate, named Princess Leia in keeping with the
Star Wars theme, is responsible for keeping him from freezing at
night. Because dwarves have a low level of the thyroid hormone,
their bodies cannot maintain constant temperatures, Miller said.
Yoda and Princess Leia currently live happily together in the

How much longer Yoda will live is unknown because, at this
point, there is no way to predict his lifespan, he added.

“Your guess is as good as mine,” Miller said.

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