showed a similar pattern to H3 after the first GSC
division (fig. S3).
The consistent asymmetric cell divisions of
GSCs could be lost under certain conditions,
such as ectopic activation of the key JAK-STAT
signaling pathway in the niche (23–25). It has
been shown that overexpression of the JAK-STAT ligand unpaired (OE-upd) induces overpopulation of GSCs (23, 24). Consistent with the
loss of asymmetry in expanded GSCs, the asymmetric distribution pattern of the histone H3 was
not observed in OE-upd testes 16 to 20 hours
after heat shock (Fig. 4). These results demonstrate that the asymmetric histone distribution
pattern is dependent on GSC asymmetric divisions. We propose a two-step process as our
favored explanation (fig. S4A; an alternative
explanation is discussed in fig. S4B): Old and
newly synthesized histones are incorporated to
different sister chromatids during S phase; then,
during mitosis, the sister chromatid preloaded
with old histones is preferentially segregated
These data reveal that stem cells preserve
preexisting histones through asymmetric cell
divisions. The JAK-STAT signaling pathway
required for the asymmetric GSC divisions
contributes to the asymmetric histone distribu-
tion pattern. This work provides a critical first
step toward identifying the detailed molecular
mechanisms underlying old histone retention
during GSC asymmetric division. These findings
in the well-characterized GSC model system will
facilitate understanding of how epigenetic infor-
mation could be maintained by stem cells or
reset in their sibling cells that undergo cellular
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Acknowledgments: We thank J. Prado for discussions to
develop a controlled gene expression system and the
FRT-MCS-SV40 Poly A-FRT plasmid; A. Talaga, A. Chin,
A. Kim, and B. Weber for experimental assistance; K. Ahmad
for plasmids containing H3, H2B, and H3.3 sequences;
A. Nakamura for the UAS-mKO-vasa strain; S. DiNardo for
the UAS-upd strain; Y. Yamashita for GSC cell cycle information
and insightful suggestions; and R. Kuruvilla, K. Zhao, Y. Zheng,
H. Zhao, M. Van Doren, D. Drummond-Barbosa, A. Hoyt,
and Chen lab members for critical reading. Supported by
NICHD/NIH grants R21HD065089 and R01HD065816, the
David & Lucile Packard Foundation, American Federation of
Aging Research, and JHU start-up (X.C.).
Materials and Methods
Figs. S1 to S4
Tables S1 to S4
13 June 2012; accepted 4 September 2012
Anuj K. Shah,1* Sendhil Mullainathan,2 Eldar Shafir3
Poor individuals often engage in behaviors, such as excessive borrowing, that reinforce the
conditions of poverty. Some explanations for these behaviors focus on personality traits of the
poor. Others emphasize environmental factors such as housing or financial access. We instead
consider how certain behaviors stem simply from having less. We suggest that scarcity changes
how people allocate attention: It leads them to engage more deeply in some problems while
neglecting others. Across several experiments, we show that scarcity leads to attentional shifts that
can help to explain behaviors such as overborrowing. We discuss how this mechanism might
also explain other puzzles of poverty.
The poor often behave in ways that re- inforce poverty. For instance, low-income individuals often play lotteries (1, 2), fail
to enroll in assistance programs (3), save too
little (4), and borrow too much (5). Currently there
are two ways to explain this behavior. The first
focuses on the circumstances of poverty, such as
1Booth School of Business, University of Chicago, Chicago, IL
60637, USA. 2Department of Economics, Harvard University,
Cambridge, MA 02138, USA. 3Department of Psychology and
Woodrow Wilson School of Public and International Affairs,
Princeton University, Princeton, NJ 08544, USA.
*To whom correspondence should be addressed. E-mail:
education (6), health (7), living conditions (8),
political representation (9), and numerous demographic and geographic variables (10, 11). Put
simply, the poor live in environments (for sociological, political, economic, or other reasons)
that promote these behaviors. The second view
focuses on personality traits of the poor (12–14).
But we suggest a more general view: Resource
scarcity creates its own mindset, changing how
people look at problems and make decisions.
To understand this hypothesis, consider how
people manage expenses. When money is abun-
dant, basic expenses (e.g., groceries, rent) are han-
dled easily as they arise. These expenses come
and go, rarely requiring attention and hardly lin-
gering on the mind. But when money is scarce,
expenses are not easily met. Instead of appearing
mundane, they feel urgent. The very lack of
available resources makes each expense more
insistent and more pressing. A trip to the gro-
cery store looms larger, and this month’s rent
constantly seizes our attention. Because these
problems feel bigger and capture our attention,
we engage more deeply in solving them. This is
our theory’s core mechanism: Having less elicits