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Two New Pseudopod Morphologies Displayed by the Human Hematopoietic KG1a
Progenitor Cell Line and by Primary Human CD34 1 Cells
By Karl Francis, Ramprasad Ramakrishna, William Holloway, and Bernhard O. Palsson
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 mm apart. Magnupodia are much thicker
and have been observed to extend more than 330 mm 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 CD341
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.
r 1998 by The American Society of Hematology.
M
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 CD341 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 implica-
ANY 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
From the Department of Bioengineering, University of California
San Diego, La Jolla, CA.
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.
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.
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.
r 1998 by The American Society of Hematology.
0006-4971/98/9210-0022$3.00/0
3616
Blood, Vol 92, No 10 (November 15), 1998: pp 3616-3623
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TWO NEW PSEUDOPOD MORPHOLOGIES
Fig 1. KG1a cell projecting a magnupod that is approximately
94-mm long toward a neighboring cell. The surface was coated with
fibronectin and a 203 objective was used. The scale bar is 50-mm
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.
tions as to the role podia play in engraftment after bone marrow
transplantation.
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 CD341 cells were obtained from
several sources. CD341 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
3617
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 CD341 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 CD341 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.
Fig 2. KG1a cell retracting a magnupod. Four images were taken at various time intervals. Image (a) was taken at t 5 0, (b) at t 5 14 seconds,
(c) at t 5 75 seconds, and (d) at t 5 150 seconds. The corresponding lengths of the magnupod are 77, 58, 42, and 14 mm, respectively, resulting in a
retraction rate of approximately 0.4 mm/s. The scale bar is 50-mm long.
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3618
Time-lapse image acquisition. Cells were imaged using an inverted
Diaphot 300 fluorescent microscope (Nikon Inc, Melville, NY) with
203, 403, and 1003 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, 1003 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,
FRANCIS ET AL
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.
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.
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
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-mm
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-mm 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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TWO NEW PSEUDOPOD MORPHOLOGIES
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.
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 laminincoated 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
3619
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
Fig 4. (a) KG1a cells displaying both podia morphologies. The cell in the upper left corner has extended a 114-mm long magnupod, whereas
the other cell has deployed multiple tenupodia. One tenupod has extended in the direction of a 6.4-mm 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-mm 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-mm long.
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3620
FRANCIS ET AL
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-mm long. The scale bar is 100-mm long.
secreting a soluble factor or to follow a trail of adhesion
molecules bound to the extracellular matrix.
Primary human CD341 cells also exhibit the same podia
formation behavior as the KG1a cells. The images in Fig 6a
through c show CD341 cells from FL, UCB, and aBM
displaying both magnupodia and tenupodia. Mobilized peripheral blood CD341 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 CD341 cells we have tested thus far.
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.
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
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TWO NEW PSEUDOPOD MORPHOLOGIES
3621
Fig 6. Primary human CD341 cells also display magnupodia and tenupodia. (a) A CD341 cell from an umbilical cord blood source displaying a
magnupod. (b) A human fetal liver CD341 cell with a very long tenupod. (c) aBM CD341 cell deploying a long magnupod. Scale bars in all images
are 30-mm long.
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 lymphocyteendothelial interaction.2 Although a precedent has been set for
this type of behavior, uropodia appear to be wider and extend
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3622
FRANCIS ET AL
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-mm long. (b) A
similar KG1a cell stained for the presence of the CD44
antigen on its surface. The scale bar is 100-mm 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.
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
CD341 KG1a cells, primary human CD341 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 CD341 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.
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TWO NEW PSEUDOPOD MORPHOLOGIES
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From www.bloodjournal.org by guest on June 18, 2017. For personal use only.
1998 92: 3616-3623
Two New Pseudopod Morphologies Displayed by the Human Hematopoietic
KG1a Progenitor Cell Line and by Primary Human CD34 +Cells
Karl Francis, Ramprasad Ramakrishna, William Holloway and Bernhard O. Palsson
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