98 ■ CHAPTER 06 Cell Division
CELLS
I
t began as a run-of-the-mill experiment. In
1989, biologists Ana Soto and Carlos Sonnen-
schein at Tufts University in Massachusetts
were studying how the hormone estrogen regu-
lates the growth of cells in the female repro-
ductive system. For their research, the duo
developed an experimental setup consisting of
human breast tumor cells growing in plastic
bottles called cell culture flasks (Figure 6.1,
top). The flasks were filled with a liquid contain-
ing a factor that prevented the cells from multi-
plying. But when estrogen was added to the
flasks, the cells grew. When estrogen was absent,
they didn’t.
One day, suddenly and surprisingly, cells
in the flasks began growing even when estro-
gen hadn’t been added. “What had worked for
years didn’t work anymore,” says Sonnenschein.
The two scientists immediately stopped their
experiments and began searching for the cause.
“It smacked of contamination,” recalls Soto,
as if estrogen had somehow gotten into the
flasks. But after weeks of searching, Soto and
Sonnenschein still couldn’t identify a source of
contamination. They became so paranoid that
they suspected someone was entering the lab at
night and secretly dripping estrogen into their
flasks.
Almost 10 years later, in August 1998, genet-
icist Patricia Hunt at Case Western Reserve
University in Ohio stared dumbfounded at
another experimental anomaly. Hunt was
studying why older women are at increased
risk of having children with chromosomal
abnormalities, like Down syndrome, in which
an individual has 47 chromosomes—the tiny,
stringlike structures in cells that contain
genes—instead of the usual 46 (see Chapter 8
for more on chromosomes). She hypothesized
that hormone levels have an impact on that
increased risk. To test her hypothesis, Huntraised groups of mice with varying levels of
hormones and checked their egg cells for abnor-
mal numbers of chromosomes (Figure 6.1,
bottom).
The experiment was almost complete when
Hunt went in to check on the control mice one
last time. A control population is a necessary
baseline for comparison against an experimen-
tal population; in this case, the control was a
group of healthy mice whose hormone levels
had not been altered. Using a light microscope,
Hunt examined mouse oocytes—precursors to
egg cells—at the moment just before the cellsFigure 6.1
Two research models, two unusual
results
Breast tumor cells (top) and mouse oocytes
(bottom) grew in unexpected ways, leading
scientists to study them more deeply.Ana Soto is a biologist at Tufts University who
studies how cell division is affected by sex
steroids. Carlos Sonnenschein, also a professor
at Tufts University, studies chemicals that
disrupt hormone systems in mammals.ANA SOTO AND CARLOS
SONNENSCHEIN