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 Previous Article | Table of Contents | Next Article 
Blood, Vol. 92 No. 10 (November 15), 1998:
pp. 3616-3623
Two New Pseudopod Morphologies Displayed by the Human Hematopoietic
KG1a Progenitor Cell Line and by Primary Human CD34+
Cells
By
Karl Francis,
Ramprasad Ramakrishna,
William Holloway, and
Bernhard O. Palsson
From the Department of Bioengineering, University of California San
Diego, La Jolla, CA.
 |
ABSTRACT |
A primitive human hematopoietic myeloid progenitor cell line, KG1a,
characterized by high expression of the CD34 surface antigen has been
observed to extend long, thin pseudopodia. Once extended, these
pseudopods may take on one of two newly described morphologies, tenupodia or magnupodia. Tenupodia are very thin and form in linear segments. They adhere to the substrate, can bifurcate multiple times,
and often appear to connect the membranes of cells more than 300 µm
apart. Magnupodia are much thicker and have been observed to extend
more than 330 µm away from the cell. Magnupods are flexible and can
exhibit rapid dynamic motion, extending or retracting in a few seconds.
During retraction, the extended material often pools into a bulb
located on the pod. Both morphologies can adhere to substrates coated
with fibronectin, collagen IV, and laminin as well as plastic. The CD34
and CD44 antigens are also present on the surface of these podia.
Primary human CD34+ cells from fetal liver, umbilical
cord blood, adult bone marrow, and mobilized peripheral blood extend
these podia as well. The morphology that these pseudopods exhibit
suggest that they may play both sensory and mechanical roles during
cell migration and homing after bone marrow transplantation.
© 1998 by The American Society of Hematology.
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INTRODUCTION |
MANY CELL TYPES have been observed to
exhibit dynamic formation and retraction of surface extensions as they
migrate. These pseudopodia may play either a sensory or mechanical role and are typically classified by their morphology. Some examples are the
bulbous lobopodia used by the parasitic amoeba Entamoeba histolytica and the broad, flat lamellipodia produced
by the amoeba Acanthamoeba
castellani.1 Mammalian cells also exhibit
pseudopods of the lamellipodia variety along with accompanying
microspikes that are fine hair-like extensions about 0.1 to 0.2 µm in
diameter and up to 20 µm in length. T lymphocytes are known to
project uropods that mediate cell-cell interaction,2
whereas neurites form longer microspikes known as filopodia that are
critical to the growth cone guidance process.3-6 The
filopodia extended by neurites can be up to 50 µm long.7
Platelets also extend active membrane processes in which dynamic
membrane ruffling is accompanied by the deployment of
microspikes.8
The acute myelogenous leukemia cell line, KG1a, was first isolated in
1980.9 A prominent phenotypic abnormality of these cells is
their inability to differentiate into functionally mature cells,
causing them to remain in an early or primitive state of development.10 Because of their primitive nature, KG1a
cells were used in a strategy to develop antibodies that recognized immature hematopoietic cells.11 The result was the first
antibody against the cell surface marker CD34, which has since become
the marker of choice in progenitor cell selection for hematopoietic studies as well as enrichment protocols for stem cell
therapies.12
The migratory and homing characteristics of hematopoietic stem cells
(HSCs) are of significant current interest, because these processes
play a major role in hematopoietic engraftment and recovery after bone
marrow transplantation. Transplantation of cells characterized by the
CD34 surface antigen induces hematopoietic reconstitution in patients
undergoing myeloablation. The homing of these cells to the marrow is a
complex and poorly understood process that likely involves chemokines
for navigation13 as well as adhesive interactions14-17 to guide them to their appropriate niches
within the bone marrow. Of the many adhesive interactions likely
involved in this process, the CD44 antigen is known to bind to
fibronectin, a common extracellular matrix component.18 In
addition to forming adhesive attachments, migration also requires the
cell to deform, extending cytoplasmic projections and generating
contractile forces as it moves.19,20 Although in principle
CD34+ cells must also undergo the same physical processes
required for motion, little is known about how they actually accomplish this task. The discovery of the mobilization of HSCs into
circulation,21 enabling the collection of an engrafting
cell population by leukophoresis, further illustrates the importance of
understanding the migratory characteristics of primitive hematopoietic
cell populations.
We have examined the migration characteristics of KG1a cells in culture
using time-lapse fluorescent microscopy. What we report here is the
characterization of two new morphologies of thin (about 1 µm or less)
pseudopods, tenupodia, and magnupodia displayed by these cells.
Tenupodia (from Latin meaning thin or tenuous) are very thin and form
in linear segments. They adhere to the substrate, can bifurcate
multiple times, and often appear to connect the membranes of cells more
than 300 µm apart. Magnupodia (from Latin meaning large or long) are
slightly thicker and have been observed to extend more than 330 µm
away from the cell. Magnupods are flexible and can exhibit rapid
dynamic motion, deploying or retracting in a few seconds. As they
retract, the extended material often pools into a bulb located on the
pod. Both morphologies can adhere to substrates coated with
fibronectin, collagen IV, and laminin as well as tissue culture-treated
plastic. We have observed the deployment of these podia during in vitro
cell migration, suggesting that they perform both sensory and
mechanical functions. These observations may have implications as to
the role podia play in engraftment after bone marrow transplantation.
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MATERIALS AND METHODS |
Cell line.
The human hematopoietic cell line KG1a was obtained from the ATCC
(Rockville, MD). Cells were received cryopreserved and then rapidly
thawed and suspended in Iscove's modified Dulbecco's medium (IMDM; GIBCO-BRL, Grand Island, NY) containing 4 mmol/L
L-glutamine, 1.5 g/L sodium bicarbonate, and 20% fetal bovine serum.
The line was maintained in an incubator at 37°C, 95% humidity, and
5% CO2. Passage was performed every 3 to 4 days (as
recommended by the ATCC). Propidium iodide (Boehringer Mannheim,
Indianapolis, IN) was used to check for cell viability following the
manufacturer's recommendations.
Primary cell sources.
Human CD34+ cells were obtained from several sources.
CD34+ cells from mobilized peripheral blood (mPB) were
obtained from donors that were mobilized with a combination of
granulocyte-macrophage colony-stimulating factor (GM-CSF) and
granulocyte colony-stimulating factor (G-CSF) cytokines. The patients'
peripheral blood was leukaphoresed and the mononuclear cells were
isolated. CD34 enrichment was performed with an immunomagnetic
separation column (AmCell, Sunnyvale, CA). Approximately 85% purity of
CD34+ cells was typically achieved. The cells were then
cryopreserved in liquid nitrogen. After rapid thawing at 37°C, they
were suspended in Meylocult H5100 media (Stem Cell Technologies Inc,
Vancouver, British Columbia, Canada) containing 12.5% fetal calf serum
and 12.5% horse serum (without additional hematopoietic growth
factors) and allowed to recover for 6 to 12 hours before staining.
Purer CD34+ preparations from fetal liver (FL), umbilical
cord blood (UCB), and adult bone marrow (aBM) were obtained using flow
cytometric sorting (FACStar Plus; Becton Dickinson, San Jose, CA). The
fluorescein isothiocyanate (FITC)-conjugated CD34 antibody used was
anti-HCPA-2 (clone 8G12; Becton Dickinson). These cells are suspended
in the same Meylocult media and are used fresh, immediately after
sorting. The number of viable cells was increased by sorting out dead
cells based on their light scattering characteristics.
Cell preparation.
For visualization, the cells were stained with the fluorescent membrane
dye, PKH26 (Zynaxis, Malvern, PA), which excites at a wavelength of 551 nm and emits at 567 nm. The staining procedure incorporates aliphatic
reporter molecules into the cell membrane so the fluorescence detected
depends on the amount of membrane in any given
location.22,23 Cells were stained following the manufacturer's guidelines. Briefly, approximately 1 million cells were
suspended in 1 mL of diluent C. PKH26 was diluted in diluent C to a
ratio of 8 µL dye to 1 mL of diluent C. The diluted dye was combined
with the cells (final concentration, 4 µmol/L) for a period of 6 minutes, after which an equal volume of Dulbecco's phosphate-buffered
saline (PBS; GIBCO-BRL) containing 1% Leptalb-7 (Intergen, Purchase,
NY) was added to stop the staining reaction. After 1 minute, an equal
volume of fresh medium was added. The cells were then spun down at
400g for 10 minutes and washed two additional times in PBS or
fresh media.
Immunostaining for surface antigens was performed using the following
technique. KG1a cells were washed in PBS (GIBCO-BRL) and then
resuspended in a isotonic, 295 mOsm sucrose solution to avoid salt
crystal formation as the media dried. Fifty microliters of the cell
suspension was allowed to dry on a glass slide. Drying was performed to
preserve the fragile pod structures, because conventional fixing
protocols resulted in damaged and missing podia. Then, 50 µL of 1:100
dilution of either CD34 (phycoerythrin-conjugated anti-HCPA-2; Becton
Dickinson) or CD44 (phycoerythrin conjugated; Pharmingen, San Diego,
CA) antibody in the isotonic sucrose solution was applied to the dried
cells and allowed to incubate at 4°C overnight before imaging the
next day. As a negative control, isotype control antibodies conjugated
to phycoerythrin (mouse IgG2b for CD44 and mouse
IgG1 for CD34; Pharmingen) were used in the same procedure.
Time-lapse image acquisition.
Cells were imaged using an inverted Diaphot 300 fluorescent microscope
(Nikon Inc, Melville, NY) with 20×, 40×, and 100×
objectives. PKH26 images were obtained using fluorescent filter set
41003 (Chroma Technologies, Brattleboro, VT). Digitized images were acquired with a cooled CCD camera (Photometrics Inc, Tucson, AZ) and
stored on an SGI O2 workstation (Silicon Graphics, Mountain View, CA). All acquisition and processing functions were controlled by
Isee software (Inovision Corp, Durham, NC), which provided complete
automation for the system.
Image processing.
Podia are not clearly visible using bright field, phase contrast, or
Hoffman modulation contrast microscopy at lower magnification, but are
readily detectable using the fluorescent membrane dye PKH26 or with a
higher power, 100× objective. The fluorescent podia are very dim
relative to the bright cells from which they emanate. For this reason,
the contrast of the fluorescent images was enhanced so that the podia
became visible. With the contrast enhanced, the image of the cell is
degraded and small pieces of membrane fragments and debris created
during the staining process appear as bright objects in the image.
Environmental conditions and cell manipulation.
The cells were kept in a constant 37°C environment by an incubator
surrounding the microscope. The incubator consisted of a large, sealed,
custom fabricated plexiglas box heated by a warm air blower controlled
by a PID temperature controller (Cole-Parmer, Vernon Hills, IL).
Control of pH to approximately 7.4 was achieved by flushing the
plexiglas box with CO2. A controller constantly sensed the
CO2 in the box and maintained its concentration at 5%.
Media evaporation was reduced to approximately 2% per day by filling
adjacent wells with water and wrapping the multiwell plates with
parafilm (American National Can, Greenwich, CT).
Cells were plated at different densities on various substrates in
plastic tissue culture dishes, 96-well plates (Costar, Cambridge, MA),
and glass microscope slides and coverslips. Other surfaces tested were
human fibronectin-coated glass coverslips, 35-mm plastic dishes, and
96-well plates coated with mouse collagen IV, mouse laminin, and human
fibronectin (Becton Dickinson, Bedford, MA).
Other experiments involved the manipulation of the cells once they
deployed their pods. A micromanipulator system (Eppendorf, Hamburg,
Germany) was used to position a standard 1.1-mm (outside diameter)
capillary tube in the cell well. The tube was bent at a 90° angle
approximately 18 mm from the end (so it could fit into the deep, small
diameter wells) by heating it with a bunsen burner. This process
prohibited the use of micropipette tips, because the heat caused the
thin glass tip to melt. Through the use of a syringe, media was gently
drawn into the pipette and then expelled causing the podia to
experience mechanical forces due to the fluid motion.
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RESULTS |
When KG1a cells are plated and allowed to incubate for approximately 1 hour at 37°C, they begin to deploy long, thin pods. The KG1a cell
shown in Fig 1 deployed a magnupod that
extended approximately 94 µm away from the cell towards a neighboring
cell. Magnupods tend to float in the medium and, if there is any fluid motion, will extend downstream, whereas the cell remains adhered to the
substrate. This phenomena is most obvious when a 10-µL drop of cell
suspension is placed on a glass slide. As the media evaporates, fluid
moves towards the edge of the drop due to capillary flow causing a
radial current.24 The cells near the edge deploy magnupods
that point radially outward.
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| Fig 1.
KG1a cell projecting a magnupod that is approximately
94-µm long toward a neighboring cell. The surface was coated with
fibronectin and a 20× objective was used. The scale bar is 50-µm
long. The contrast of the image has been enhanced so that the podia are
visible. Unenhanced images of the cells have been inserted into the
figure so the actual size of the cells is more obvious.
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Magnupods are capable of rapidly retracting as seen in the time
sequence of Fig 2a through d. Shorter
magnupods (<20 µm) can retract into the cell body in a matter of
seconds, whereas the longer podia pool the membrane into bulbs that
form along the length of the pod. The cell shown in Fig 2 was observed
to retract its magnupod at a rate of 0.4 µm/s. Extension and
retraction of magnupods is not a continuous process. Once the magnupod
has extended, it is not uncommon for it to remain deployed for several
hours. The stimulus responsible for the extension or retraction of
magnupodia is unknown at this time. Other interesting features of the
magnupod morphology are that they can extend to great distances away
from the cell, as seen in Fig 3, which
shows a magnupod with a total length of greater than 330 µm. The tip
of the magnupod is out of focus, indicating that it is floating freely
above the surface. However, magnupods are also capable of forming
attachments to the substrate. These can be identified by applying
mechanical forces with a micropipette. The attachment was determined by
using the micropipette to induce fluid flow around the cell. The cell and the pod deform and may float away, except where it is anchored to
the substrate (data not shown). However, these attachments are not
continuous along the magnupod, suggesting a nonuniform distribution of
adhesion complexes.
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| Fig 2.
KG1a cell retracting a magnupod. Four images were taken
at various time intervals. Image (a) was taken at t = 0, (b) at t = 14 seconds, (c) at t = 75 seconds, and (d) at t = 150 seconds. The
corresponding lengths of the magnupod are 77, 58, 42, and 14 µm,
respectively, resulting in a retraction rate of approximately 0.4 µm/s. The scale bar is 50-µm long.
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| Fig 3.
Two KG1a cells displaying extremely long magnupodia. The
total length of the podia extended by the cell on the left is over
330-µm long. The tip of one magnupod is out of focus, indicating that
it is floating above the plane of focus. The scale bar in this image is
100-µm long. Enhancing the contrast of this image so that the podia
become visible has also caused membrane fragments and debris to appear
as bright objects.
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Tenupodia are the second new pod morphology found on KG1a cells.
Tenupodia are morphologically substantially different from magnupodia
and they exhibit different behavior. An example of tenupod formation is
given in Fig 4. Figure 4a shows a KG1a cell that is sprouting tenupods on a laminin-coated substrate (at the top is
a second KG1a cell projecting a magnupod). The tenupod appears as
linear segments that deploy from a common point of origin on the cell
surface. They extend away from the cell body and may branch or turn at
specific points. One of the tenupods, upon encountering a 6.4-µm
plastic bead, navigates around it by bifurcating. This bifurcation
behavior is also seen in Fig 4b, in which a cluster of tenupods extend
away from a single cell. Tenupodia are more prevalent on surfaces
coated with fibronectin, laminin, and collagen IV than on glass or
plastic, suggesting that interactions with the surface play an
important role in determining podia morphology. Finally, tenupods have
been observed to connect the membranes of two different cells located
more than 300 µm apart. A typical example of this behavior is seen in
Fig 5, which shows tenupods extended in a
linear fashion directly to the neighboring cell. In contrast, multiple
tenupods from the cell in Fig 4a deployed along a more circuitous route
as they converged on a region to the upper right of the cell, changing
direction in a seemingly nonrandom manner, as if some factor were
acting to bias the direction of their extension. Taken together, these
observations suggest that tenupodia sense and respond to environmental
cues. Capabilities such as these would allow tenupods to home in on a
distant source that was secreting a soluble factor or to follow a trail
of adhesion molecules bound to the extracellular matrix.
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| Fig 4.
(a) KG1a cells displaying both podia morphologies. The
cell in the upper left corner has extended a 114-µm long magnupod,
whereas the other cell has deployed multiple tenupodia. One tenupod has
extended in the direction of a 6.4-µm plastic bead before bifurcating
and heading off to the right of the image, where it appears to have
located whatever factor was attracting it. The scale bar is 100-µm
long. (b) This inset image shows a KG1a cell with a highly branched
tenupod network that has extended toward a neighboring KG1a cell that
was migrating via a lamellapodia. The scale bar is 50-µm long.
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| Fig 5.
Tenupods can extend toward other cells and appear to
connect the membranes. In this image, tenupodia connect the membranes
of 3 neighboring cells. The longest tenupod is 310-µm long. The scale
bar is 100-µm long.
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Primary human CD34+ cells also exhibit the same podia
formation behavior as the KG1a cells. The images in
Fig 6a through c show CD34+
cells from FL, UCB, and aBM displaying both magnupodia and tenupodia. Mobilized peripheral blood CD34+ cells also behave in a
similar manner (data not shown). In more than 40 experiments with
primary cells, we have observed podia formation in greater than 75% of
the experiments. Magnupod and tenupod formation by the primary cells
was not as consistent as with the KG1a cell line, possibly due to donor
variability25 or sensitivity to cell processing,
preparation, and culture conditions. Interestingly, these podia
morphologies appear to be common among all the sources of primary
CD34+ cells we have tested thus far.
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| Fig 6.
Primary human CD34+ cells also display
magnupodia and tenupodia. (a) A CD34+ cell from an
umbilical cord blood source displaying a magnupod. (b) A human fetal
liver CD34+ cell with a very long tenupod. (c) aBM
CD34+ cell deploying a long magnupod. Scale bars in all
images are 30-µm long.
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The CD34 and CD44 surface antigens are also associated with podia
formation in KG1a cells, as shown in Fig 7a
and b. The magnupod in Fig 7a has stained brightly for the CD34
antigen, whereas staining for CD44, a known surface adhesion molecule,
has also shown its presence on the surface of the podia in Fig 7b.
Negative controls were always dim and no detectable nonspecific binding
was observed. The fact that these podia were detected using antibody
staining and also on unstained cells at high magnification indicates
that they are not an artifact of the PKH26 membrane dye staining. At the time of observation, approximately 95% of the KG1a cells were viable. Primary cells were not checked for viability. KG1a cells that
were killed by heating to 65°C for 15 minutes did not deploy any
podia, showing that, as expected, their extension is an active process.
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| Fig 7.
(a) A KG1a cell displaying a magnupod that has been
stained with an antibody against the CD34 surface marker. The scale bar
is 50-µm long. (b) A similar KG1a cell stained for the presence of
the CD44 antigen on its surface. The scale bar is 100-µm long. Note
that the antibody staining of the cell bodies in these fluorescent
images is not as bright as the PKH26 staining, resulting in more
uniformly enhanced images.
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DISCUSSION |
Many cell types exhibit dynamic surface extensions when they migrate or
change shape. Such extensions are capable of dynamic formation and
retraction with typical velocities for microspikes and lamellipodia on
the order of 0.1 µm/sec.1 In neurites, filopodia are
believed to play a role in the progression of axon elongation by aiding
the assembly of microtubules.26 These filopodia extend from
the lamellipodial region, acting as radial sensors, and are crucial to
growth cone navigation.3-6 They have also been found to
carry receptors for certain cell adhesion molecules.27 Mature blood cells can also deploy cytoplasmic extensions. Recently, structures termed uropods have been found on T lymphocytes2 that form during lymphocyte-endothelial cell interaction. T cells have
been found to use uropods to contact and communicate directly with
other T cells. Uropod development was promoted by physiologic factors
such as chemokines. Pseudopodia, therefore, can display a variety of
dynamic and morphological properties while performing a spectrum of
functions in many different cell types related to migration and
communication.
We have discovered that cells of the primitive human hematopoietic
myeloid progenitor cell line, KG1a, are capable of extending two
fundamentally new pseudopodia morphologies. These podia (1) exhibit
dynamic extension and retraction behavior, (2) can adhere to the
substrate they are migrating over, (3) appear to be guided by
environmental stimuli, and (4) have antigens for CD34 and CD44 antibodies on their surfaces. However, magnupodia and tenupodia are
distinctly different morphologies exhibited by KG1a cells and may
therefore perform specialized migratory functions that are unique to
primitive hematopoietic cells, such as homing.
Magnupods have morphological similarities with the long (50 µm), thin
(0.2 µm) filopodia found on neurites.28,29 However, they
differ in that magnupod extension occurs to much greater distances
(>300 µm, or roughly 30 cell diameters) from the main cell body,
and they exhibit rapid dynamic behavior, retracting more than eight
times faster than neurite filopodia. Magnupods may remain extended for
several hours, whereas neurite filopodia extend and retract
continuously. It has been suggested that the switch between neurite
filopodia extension and retraction reflects a shift in the actin
polymerization and depolymerization rates.29 This
difference in dynamic characteristics may indicate structural as well
as functional differences between filopodia and magnupodia. Whereas
filopodia appear to act primarily as sensory appendages in neurites,
magnupods may play a more mechanical role in migration, similar to
lamellipodia. Magnupods can adhere to the substrate at specific points,
and recently it has been reported that the migratory properties of KG1a
cells are enhanced when they are crawling over a substrate coated with
fibronectin.30 One may speculate that a deployed magnupod
drifts freely until its surface adhesion complexes encounter suitable
binding sites on the substrate. A retraction would then drag the cell
body towards the site of adhesion. Additionally, a retraction may also
be hindered by multiple point attachments, with the result being that
the podia material pools into bulbs along the length of the magnupod.
This dynamic behavior makes the magnupod morphology uniquely different
from filopodia.
Tenupodia, on the other hand, may perform a more sensory type role.
They are thinner and probably do not have the structural characteristics necessary to drag a cell. A peculiar feature of this
morphology is that they extend in perfectly linear segments and often
in a line directly toward another cell. If the tenupod stops growing,
it will likely bifurcate or turn about a fixed point and continue its
linear propagation until it encounters its target. This type of
guidance may be mediated by diffusible factors released by cellular
targets.31,32 It is estimated that the domain that a single
cell can effectively communicate in by using a soluble signal is about
250 µm in size and that the communication within this domain takes
place in 10 to 30 minutes.33 These theoretically derived
estimates correlate well with the times and distances that tenupods
travel to reach or connect with a neighboring cell. Uropods also
exhibit similar sensory properties in that they have been observed to
contact, capture, and recruit additional T cells during
lymphocyte-endothelial interaction.2 Although a precedent
has been set for this type of behavior, uropodia appear to be wider and
extend only a few cell diameters away from the cell, nowhere near the
extension distances of tenupods. Ultrastructural analysis of
antigen-presenting dendritic cells indicates that these cells also
deploy extensions that are much longer than the cellular
body.34 However, these observations show that the extension constituted a major part of the cellular volume, whereas the volume of
tenupods is insignificant compared with the cell. This high surface
area to volume ratio could also make the tenupod highly sensitive to
environmental signals.5 Tenupods are also more prevalent
when the cells are cultured on surfaces coated with extracellular
matrix components such as fibronectin, laminin, or collagen IV. This
indicates that adhesion and contact guidance play a role in their
formation and morphology. Whether it is via soluble signals, surface
adhesion, or both, environmental interactions clearly influence the
morphology of tenupods, suggesting that the function they perform is
sensory in nature.
The CD44 antigen has been implicated as playing an important role in
homing and hematopoiesis35,36 due to its ability to bind to
a variety of extracellular matrix components, including fibronectin and
collagen.18,37 Recently, it has been suggested that the
CD34 antigen also participates in adhesive interactions thorough an
indirect mechanism, signaling changes in the surface profile of other
adhesion molecules.38 Furthermore, there are intracellular
stores of CD34 protein that can be translocated to the plasma membrane
in response to extracellular signals.39 Compositional data
such as these indicate that a relationship between key surface markers,
homing-related adhesive proteins, and pseudopod morphology may exist.
Perhaps the most interesting finding is that these podia are found on
primary human hematopoietic cells. In addition to the CD34+
KG1a cells, primary human CD34+ cells from FL, UCB, aBM,
and mPB that we have tested as well as mouse fetal liver cells all
display these new pseudopod morphologies. Therefore, these new
morphologies are not a particular property of the KG1a cell line. It
should also be noted that KG1a cells and primary human
CD34+ cells extend lamellipodia-type processes during
migration. When imaged in time-lapse mode, these cells also
exhibit the classical crawling behavior as described in the
literature.1,19,40 Of the plated cells, only about 1% to
10% actually deploy magnupods or tenupods at any given time.
Given that (1) known pseudopodia types perform specific functions in
communication and migration, (2) primitive hematopoietic cells extend
long thin pseudopods, and (3) important activities of primitive
hematopoietic cells are communication and migration, it is possible
that the morphology and physiologic activity of magnupodia and
tenupodia are related to the function they perform while the cell is
homing after transplantation. These data may significantly impact our
thinking about how primitive hematopoietic cells migrate and the role
of cytoskeletal structures in the clinically important process of stem
cell engraftment.
| |
ACKNOWLEDGMENT |
The authors acknowledge the assistance of Dr Anthony D. Ho, Dr Ping
Law, Dennis Young, Sandy Peterson, Dr Ewa Carrier, Jody Donahue, and Dr
Shiang Huang of the USCD Bone Marrow Transplant Program in supplying
primary human and mouse cells and Dr Duk-Jae Oh and Mahshid Palsson of
the UCSD Bioengineering Department for maintaining the cell lines and
assisting with cell preparation.
| |
FOOTNOTES |
Submitted March 11, 1998;
accepted July 9, 1998.
Supported by Grant No. NAG9-652 from NASA, a grant from the Charles H. Stern and Anna S. Stern Foundation (La Jolla, CA), and National
Institutes of Health Grant No. RO1HL59234-01.
The publication costs of this
article were defrayed in part by
page charge payment. This article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. section
1734 solely to indicate this fact.
Address reprint requests to Bernhard O. Palsson, PhD, Department of
Bioengineering, University of California San Diego, 9500 Gilman Dr,
Mail Code 0412, La Jolla, CA 92093-0412.
| |
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Abstract
Introduction