Nick Barker talks with
ScienceWatch.com and answers a few questions about
this month's Fast Moving Front in the field of Molecular
Biology & Genetics. The author has also sent along
images of their work.
Article: Identification of stem cells in small
intestine and colon by marker gene Lgr5
N;van Es, JH;Kuipers, J;Kujala, P;van den Born,
M;Cozijnsen, M;Haegebarth, A;Korving, J;Begthel, H;Peters,
Journal: NATURE, 449 (7165): 1003-U1 OCT 25 2007
Addresses: Hubrecht Inst, Uppsalalan 8, NL-3584 CT Utrecht,
Hubrecht Inst, NL-3584 CT Utrecht, Netherlands.
Antoni Van Leeuwenhoek Hosp, Netherlands Canc Inst, NL-1066
CX Amsterdam, Netherlands
Why do you think your paper is highly
The intestine is a popular choice for scientists wanting to study the
regulation of tissue renewal because it is the most rapidly self-renewing
organ in the body, with the epithelium being completely regenerated every
5-7 days in mice and humans.
It has been known for many decades that this regeneration process is driven
by a small population of stem cells residing in pockets (termed crypts)
within the gut wall. However, their precise identity has proved elusive due
to a lack of specific markers that distinguish them from other cell types
present in the crypts.
In the Nature article we report our discovery of the first unique
marker, Lgr5 (Leucine-rich G Protein-Coupled Receptor 5) for these
intestinal stem cells. We describe the generation of a new mouse model
which allows us to perform in-vivo lineage tracing from Lgr5+ve
cell populations, providing solid functional evidence of stem cell
identity. This paper was also the first to challenge the current dogma that
adult stem cells should be quiescent—we showed the Lgr5+ve stem cells
to be proliferating every 24 hours, which we believe makes more sense
considering the large number of new cells that need to be generated in the
crypts each day to sustain epithelial renewal.
Finally, we describe preliminary data that Lgr5 is likely to be a specific
marker for stem cell populations in other rapidly regenerating organs such
as the stomach, skin, and mammary gland. Ongoing lineage tracing
experiments confirm this, thereby establishing Lgr5 as a broad marker for
adult stem cells.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
The paper largely details a new discovery—namely the identification
of Lgr5 as the first marker of cycling stem cells in the small intestine
Would you summarize the significance of your paper
in layman’s terms?
The intestine is basically a long tube, whose inner lining (the epithelium)
is largely responsible for efficiently absorbing nutrients and water from
our diet and compacting the left-over material into feces for subsequent
"disposal". Within this hostile environment, the epithelium is constantly
being subjected to mechanical shearing and nasty bug attack as digested
food/water passes through, which means it rapidly wears out and needs
We’ve known for a long time that special cells called stem cells are
responsible for ensuring this constant renewal of the epithelium, but until
now we had no way of identifying them. We recently solved this problem when
we found a gene called Lgr5 to be expressed only on these stem cells in the
epithelium. This now allows us to intensively study the stem cells and
improve our understanding of how tissue renewal is controlled in the
Armed with this knowledge we expect to be able to better understand why
this renewal process breaks down in human diseases such as Crohn's disease,
inflammatory bowel disease, and cancer. Ultimately, we hope to purify the
stem cells from the intestine using markers such as Lgr5 for helping to
repair damaged intestines, or even other adult tissues.
How did you become involved in this research and
were any particular problems encountered along the way?
We have been working on the role of the Wnt signaling pathway in intestinal
renewal and cancer for the past decade. The Wnt pathway exerts its effects
by controlling the expression of a select set of target genes influencing
various biological processes ranging from cell proliferation and migration
to cell differentiation and death.
In 2002, we found that Lgr5 is one such Wnt target gene which has a unique
expression pattern in the intestinal crypts. These Lgr5 cells turned out to
be identical to a population of cells termed crypt base columnar cells
(CBC) by Charles Philippe Leblond, Matthew Bjerknes, and Hazel Cheng in the
early 1980s—they proposed that these CBC cells were good candidates
for the elusive stem cells, but had no direct way of proving this. We
therefore set out to test this hypothesis using Lgr5 a specific marker for
the CBC cells.
The lack of commercial antibodies against this cell-surface receptor
together with the lack of in-vitro assays for assaying intestinal stem
cells dictated that we had to pursue an in-vivo lineage tracing
approach in order to assess the stem cell capacity of these Lgr5 cells.
This meant embarking on a lengthy project to generate a mouse model
(Lgr5-EGFP-ires-CreERT2) that would allow us to perform this
in-vivo lineage tracing when combined with an inducible reporter
mouse strain. Ultimately, this proved very successful and has also allowed
us to determine that Lgr5 is marking stem cell populations in other tissues
including the stomach, skin, and mammary gland.
Where do you see your research leading in the
The mouse model described in the Nature article not only allows us
to perform in-vivo lineage tracing, but also allows us to isolate
and purify the stem cells from the intestine (and other Lgr5+ve organs) by
virtue of the fact they express a fluorescent marker GFP (Green Fluorescent
Protein). This has allowed us to set up an in-vitro culture system
that allows us to grow new pieces of intestine from single Lgr5 stem cells
(Sato, T. et al., Nature 459:262, 2009).
Although this is currently limited to the generation of very small pieces
of epithelium in the laboratory, future advances in the technique may
facilitate production of intestinal pieces large enough to have therapeutic
value (Crohn's disease patients and cancer patients for example). We hope
to set up similar culture systems using Lgr5 stem cells from other adult
tissues to explore similar therapeutic opportunities in a range of human
We are also currently investigating the function of the Lgr5 gene on the
stem cells using knockout mice and are actively pursuing the ligand for
this orphan GPCR. Having identified the stem cells, we can now investigate
their role in cancer. We have already shown that mutated intestinal stem
cells are the likely source of colon cancer (Barker, N. et al.,
Nature 457: 608, 2009). Future studies will further explore the
contribution of Lgr5 stem cells to epithelial cancers.
Do you foresee any social or political implications
for your research?
The ability to isolate various adult stem cell populations using Lgr5 as a
specific marker will hopefully allow us (and others) to exploit their
capacity for effecting tissue renewal for therapeutic use. Assessing the
role of the Lgr5 stem cells in various cancers will also improve our
understanding of cancer development and may ultimately translate into the
generation of novel therapies.
Dr. Nick Barker
Utrecht, The Netherlands