5
million
Number of people
infected with
cholera each year
Number of people
who die of cholera
thousand each year
Heart cells replenish throughout life a phenomenon that serves as a birth-
mark for new cells. By looking at DNA
Past nuclear testing allowed researchers to track cell birth from people born before 1955, when
carbon 14 levels began to spike in Sweden,
researchers could see when heart cells
first formed. (Cells that didn’t divide after
a person was born wouldn’t contain car-
bon 14.) The team also inferred cells’ birth
dates by matching cells’ carbon 14 levels
to the annual atmospheric levels.
Frisén and his colleagues found that
samples from people born before 1955
did indeed have carbon 14 in heart mus-
cle cell DNA, indicating that the cells had
been created after the person’s birth.
Using DNA samples from many hearts,
the researchers estimated that a 20-year-
old renews about 1 percent of heart muscle cells in a year. By age 75, the rate of
cell turnover slows to about 0.4 percent
a year. This means that a 50-year-old has
only about 55 percent of the heart muscle cells he or she was born with, while
the remaining 45 percent of the cells
were generated later.
By Laura Sanders
By monitoring carbon 14 originally emitted from Cold War–era nuclear bomb
tests, researchers have found that heart
muscle cells continue to divide throughout adulthood. The low-level cell renewal
may eventually be exploited to treat
damaged hearts, says study coauthor
Jonas Frisén of the Karolinska Institute
in Stockholm.
The finding, appearing in the April 3
Science, contradicts the belief of many
scientists that heart muscle cells present
at death have been around since birth.
“The dogma has always been that cell
division in the heart pretty much stops
after birth,” says Charles Murry of the
University of Washington in Seattle,
whose commentary on the new research
appears in the same issue of Science. “In
medical school, we teach that you’ll die
with the heart cells you’re born with.”
To figure out whether the cells continue to be regenerated throughout life,
researchers took advantage of an inadvertent marker that has found its way
into people’s cells. Aboveground nuclear
bomb tests during the Cold War led to
skyrocketing levels of the radioactive
isotope carbon 14 in the environment.
After a testing ban took effect in 1963,
atmospheric carbon 14 levels began to
drop, giving each year since a distinctive,
signature level of the isotope. Humans
ingest carbon 14 through their diet, with
plants incorporating it into their cells
during photosynthesis.
“The carbon 14 in the atmosphere is
mirrored in bodies,” Frisén says.
When cells divide, they can use
some of the carbon 14 to build DNA,
NEWS BRIEFS
Immunity to cholera hindered
Intestinal parasites seem to limit a person’s ability to fend off cholera, a study
conducted in Bangladesh shows. the
finding, which appears online March 31
in PLoS Neglected Tropical Diseases,
might explain why vaccines against
cholera have shown only spotty effectiveness and suggests that vaccination
campaigns should be preceded by programs to wipe out parasites.
Blood and feces samples from 361
people hospitalized with severe cholera
from 2001 to 2006 were collected and
analyzed by Jason Harris of Harvard
Medical School and Massachusetts
General Hospital in Boston and his colleagues. they found that patients with
intestinal worms had markedly poorer
antibody production against the toxin
made by the cholera microbe than
those without the worms. these results
suggest there may be a similarly weak
response in people getting vaccinated,
the researchers say. —Nathan Seppa
Prions common in yeast
Prions may be more widespread than
previously thought, researchers at the
whitehead Institute for Biomedical
Research in Cambridge, Mass., report
in the April 3 Cell. Baker’s yeast was
previously known to have six native
prion proteins, none of which appear
harmful. A team led by Howard Hughes
Medical Institute investigator Susan
lindquist found that 19 other proteins
contain prion-forming domains — a
structure that allows the protein to
change its shape and function, and
to spread the altered form to other
proteins. One of the proteins, Mot3p,
was fully characterized and found to
meet all criteria for a prion. “It is logical
to suggest that there are even more
prions around,” says Yury Chernoff of
the Georgia Institute of technology in
Atlanta. — Tina Hesman Saey
HPV test beats Pap smear
A test for human papillomavirus infection is better than the standard Pap
smear at catching cervical cancer early,
researchers report. the study of women
age 30 and over in India makes the
case for changing screening practices,
particularly in low-income countries,
since the HPV test would require fewer
doctor visits, a team reports in the
April 2 New England Journal of Medicine.
“this study clearly shows that HPV
screening is more sensitive to picking up precancerous lesions than the
other tests,” says the study’s coauthor
Rengaswamy Sankaranarayanan of the
world Health Organization’s International Agency for Research on Cancer in
lyon, France. — Nathan Seppa
