Stem cells find their niche

1
Stem cells find their niche ALLAN SPRADLING,
DANIELA DRUMMOND-BARBOSA TOSHIE KAI
2
Concept of Niches
Stable custom environment for stem cells Niches
are subsets of tissues and extracellular subsets
that can indefinitely house one or more stem
cells and control their self-renewal and
progeny production in vivo Many niches have
one or more specialized cell groups like the
skin, GI tract Extracellular matrix and
adhesion molecules (basement membrane) may help
secure the niches spacially and may modulate the
concentration of adhesive and other signalling
molecules
3
Figure 1 Niche structure. Niche cells (green)
underlying a basement membrane signal to stem
cells (red) to block differentiation and regulate
division. When a lineage mechanism prevails
(lower mitotic cell), the stem cell divides such
that one daughter retains its connections to the
niche, while the other (yellow) becomes
untethered and begins to differentiate. When a
population mechanism prevails (upper mitotic
cell), stem cell division may be either symmetric
(shown) or asymmetric (not shown), as determined
by local factors. ECM, extracellular matrix.
4
Figure 2 Manipulating niches. a, Replacement
assay to identify niches. Labelled stem cells
(blue) are introduced into a tissue. If one or
more of the introduced cells becomes associated
stably with a particular tissue region and
subsequently functions as a stem cell, then the
existence and location of a stem cell niche
(green) is inferred. b, Cell marking experiments.
Marking a single stem cell in vivo (blue), and
following the number and location of marked
progeny cells reveals its regulatory behaviour.
When the stem cell follows a lineage mechanism,
the number of labelled stem cells remains
relatively constant over many stem cell cycles.
When the initially labelled stem cell follows a
population mechanism (bottom), initially mosaic
niches will sort out stochastically into niches
that have all labelled or all unlabelled cells.
5
Figure 3 Male germ cell niches. a, A
cross-section of part of a seminiferous tubule of
a mouse testis is shown to illustrate the
approximate location and properties of the
mammalian germline stem cell niche. The stem
cells also known as Asingle (As) cells (red)
constitute a minority of the basal germ cells in
contact with the basement membrane (green). Most
other basal cells (yellow) are part of growing
germ cell cysts, whose members are interconnected
by ring canals. As development proceeds, the
cysts leave the basement membrane and move in a
highly ordered manner towards the lumen of the
tubule (top). All developing germ cells are
surrounded by Sertoli cells (green). It is not
known whether the region of the Sertoli cell or
basement membrane near the stem cells are
specialized (dark green). b, A sagittal section
of the distal tip of the Drosophila testis is
drawn schematically and leaves out most of the
cells for clarity. The hub cells (green) are
attached to 59 groups comprising one germline
stem cell and two cyst progenitor stem cells
(red). The basement membrane (green) may be
thinner and specialized (dark green) near the
hub. Germline stem cell daughters called
gonialblasts are encased by two cyst cells, begin
to differentiate, and move posteriorly away from
the hub. After four more divisions, the cyst
cells (yellow) cease division and synchronously
enter meiosis.
6
transit amplifying cells
Outer root sheath
Inner root sheath
Figure 5 Epithelial stem cell niches. a,
Mammalian epidermal stem cells. A hair follicle
and a segment of adjacent skin is illustrated.
The dermal papilla (DP) signals to matrix stem
cells (red) located across a basement membrane
(green). Matrix cell daughters (yellow)
differentiate into a variety of cell types,
including the medulla, cortex and cuticle of the
hair shaft (brown), the inner root sheath (IRS)
and the outer root sheath (ORS). About two-thirds
of the way up an anagen follicle lies the bulge
an expanded region that contains long-term stem
cells (red). These cells periodically replenish
(arrows) the matrix cells, and also help maintain
the sebaceous gland (SG) and the epidermal stem
cells (red, top layer) that lie against the
basement membrane (not shown) overlying the basal
layer in interfollicular regions. b, A mammalian
gut crypt is a tube of cells arrayed on a
basement membrane (green). Stem cells (red) are
located in the basal region along with Paneth
cells, but their exact location is variable and
both types account for only a fraction of the
cells present in the regions shown. A portion of
the basement membrane in the stem cell region may
be specialized (dark green). Stem cell progeny
(yellow) known as transit amplifying cells (TA)
move upwards and differentiate. Underlying
mesenchymal cells (green) send signals that help
regulate stem cell activity.
Dermal papilla produce FGF-7, BMP-4, KGF
7
osetoid
osteoblasts
Role of osteoblasts and hematopoiesis
hsc
Blood cells
Osteobalst output 0.01 of blood cells (350
bill/day)
Stromal cell cultures express OB markers OB
express hematopoietic cytokines
msc
8
(No Transcript)
9
Bmpr1a/b signaling negative on osteoblasts,MSC
proliferation Bmpr1a -/- embryonic lethal with
major defects in blood formation Authors use
conditional KO of Bmpr1a Mating Bmpr1a fx/fx
with Mx1-Cre (poly IC induction) Also used
triple genotype mice bearing Mx1-Cre, Bmpr1a
fx/fx, and Z/EG alleles
10
(No Transcript)
11
Due to decreased BM cavity
LT
ST
Transplanted (2 x 103) with WT (ly 5.1) into
control vs Brmp1a mutants
Transplanted (2 x 103) with Brmp1a (ly 5.2) into
control vs WT recipients (ly5.1) It is the
microenvironment
In competitive repop studies using whole BM,
Bmpr1a wins out 21 (data not shown)
12
TBLA
13
Poly IC induction
14
(No Transcript)
15
Triple geneotype mice (correct targeting to
Bmpr1a region)
16
(No Transcript)
17
33
N-Cadherin Osteoblasts (per section)
78
18
SNO spindle shpaed osteoblast N-cathedrin cells
19
Possible mechanisms

• Intrinsic changes in stem cells that either
  promote self renewal or decreased apoptosis
• Internal defect in differentation
• External influence of microenvironment

Wild type to Bmpr1a transplantation (3 mo 1.6-2.0
x WT donor) Ectopic Trabecular bone-like
area Increased of HSCs in TBLA No differnce in
MSC per femur (data not shown) 10X increased bone
volume 3 x osteoblasts Same osteoclasts
20
Osteoblastic cells regulate the haematopoietic
stem cell niche L. M. CALVI1,,
G. B. ADAMS3,, K. W. WEIBRECHT3, J. M. WEBER1,
D. P. OLSON3, M. C. KNIGHT4, R. P. MARTIN3,
E. SCHIPANI4, P. DIVIETI4, F. R. BRINGHURST4,
L. A. MILNER2, H. M. KRONENBERG4 D. T. SCADDEN3

Nature 425841
21
BMT-male PTHinreased a Ability to reconstitute
female WT By real time DNA PCR for Y
Figure 1
Nature 425841
22
Increased Jag-1 in tg
Increased jag/osteopontin
Stromal cells from from tg (n6) And wt (n6)
improves support Of LTC-IC..no CFU data
HSC expansion mediated By stromal cells
Increased NICD In tg lin-Scac-Kit
Gamma-secretase of notch
Figure 2
Nature 425841
23
When WT stroma is grown in the presence of PTH,
the Effect same as tg stroma No effect of PTH
alone
Increased alk phos OB
Figure 3
Effect blocked by Gamma-secretase inhibitor
Nature 425841
24
PTH was administered for one month prior to
myeloablative BMT and animals were given limiting
numbers of donor stem cells
Figure 4a
Nature 425841
25
Histology 4 weeks Post-transplant
Figure 4b-e
Nature 425841
26
Figure 1 Birth control for stem cells. The niche
that regulates the birth and differentiation of
blood-forming (haematopoietic) stem cells is
formed of osteoblasts (a type of bone-marrow
cell) that line the inner surface of bone. Zhang
et al.7 showed that depleting osteoblasts of a
receptor for bone morphogenetic protein (BMP)
caused a doubling in both the osteoblast
population and the stem-cell population. Calvi et
al.8 found a parallel expansion of the stem-cell
population when they increased the numbers of
osteoblasts by using parathyroid hormone (PTH).
Lemischka et al Nature 425 778, 2003
Nature 425778