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HEMATOPOIESIS
From the Departments of Pathology, Pediatrics, and
Developmental Biology, Stanford University School of Medicine, CA; the
Reproductive Genetics Unit, Department of Obstetrics and Gynecology,
University of California, San Francisco; and the Gene Expression
Laboratory, The Salk Institute for Biological Studies, La Jolla, CA.
Pbx1 is the product of a proto-oncogene originally discovered at
the site of chromosomal translocations in acute leukemias. It binds DNA
as a complex with a broad subset of homeodomain proteins, but its
contributions to hematopoiesis have not been established. This paper
reports that Pbx1 is expressed in hematopoietic progenitors during
murine embryonic development and that its absence results in severe
anemia and embryonic lethality at embryonic day 15 (E15) or
E16. Definitive myeloerythroid lineages are present in
Pbx1 Hematopoiesis involves the production of a diverse
array of mature blood cells via a hierarchy of progenitors with
progressively more limited differentiation and self-renewal potential
and is orchestrated by a complex array of regulatory proteins (reviewed by Tenen et al1). Several of these regulatory proteins are transcription factors originally discovered as the products of proto-oncogenes targeted by chromosomal aberrations in hematologic malignancies. One of these is Pbx1, which was identified by virtue of
its disruption in t(1;19) chromosomal translocations in a subset of
pediatric acute lymphoblastic leukemias.2,3 The highly related genes Pbx2 and Pbx3 were subsequently
discovered on the basis of their homology to Pbx1 but have
yet to be implicated in neoplasia or other diseases.4 Pbx
proteins are mammalian homologues of the extradenticle (Exd)
protein, which functions as a cofactor for Hox transcription
factors in Drosophila.5 Like Exd, Pbx proteins
possess a divergent homeodomain DNA-binding motif and interact
physically with a subset of Hox proteins to enhance their DNA-binding
affinities and specificities. In addition, homeodomain proteins of the
Meis family are prevalent intracellular partners for Pbx proteins,
control their nuclear localization, and promote cooperative DNA
binding.6-8 The t(1;19) rearrangement fuses the
homeodomain of Pbx1 to the transcriptional activation domains of the
immunoglobulin enhancer-binding protein E2a. The E2a-Pbx1
chimeric oncoprotein retains the ability to bind DNA as a complex with
Hox, but not Meis, proteins6 and may contribute to
leukemogenesis by aberrant activation of Pbx1/Hox target genes.
Recently, evidence has emerged implicating Hox transcription factors as
master regulators of hematopoietic cell fate decisions and
leukemogenesis (reviewed by Magli et al9). Hox
gene expression in subsets of CD34+ progenitor cells from
normal human bone marrow is developmentally regulated in a
stage-specific manner.10 Perturbations of Hox gene expression in primary murine hematopoietic progenitors have pronounced effects on their proliferation and differentiation in vivo
and in vitro, including leukemic transformation.11,12 Deregulated Hox expression has also been implicated in human
hematologic malignancies, providing circumstantial support for the
importance of Hox-dependent transcriptional regulation in
the normal development of the hematopoietic lineages (reviewed by
Look13). Targeted disruption of select Hox
genes in mice has demonstrated that the encoded homeodomain
transcription factors are required for normal hematopoiesis.14-16 Taken together, these data suggest
that the establishment and maintenance of definitive hematopoiesis in
mammals depends on the transcriptional regulatory functions of several Hox proteins.
Given its role as a Hox DNA-binding cofactor and leukemic oncoprotein,
Pbx1 is likely to be required for hematopoietic development; however,
its expression patterns and specific contributions during hematopoiesis
are unknown. Here we demonstrate that Pbx1 is expressed during
embryonic hematopoiesis and that its targeted disruption leads to
substantial defects in hematopoietic progenitors with erythroid-differentiation potential resulting in severe fetal anemia
and death by embryonic day 16 (E16).
Generation of Pbx1 knockout mice
Hematocrit determination
Immunohistochemistry Embryos were fixed in Bouin fixative and embedded in paraffin. After dewaxing and microwave antigen retrieval in 0.5 M Tris, pH 10, sections of embedded embryos were stained with a Pbx1b-specific monoclonal antibody (mAb).17 Secondary staining was performed with a biotinylated goat antimouse antibody followed by strepavidin-conjugated horseradish peroxidase (HRP).Western blotting Lysates were prepared from fetal liver (FL) cell suspensions or from fractionated FL cells by boiling in sodium dodecyl sulfate (SDS) sample buffer and shearing through a 28-gauge needle. Separate nuclear and cytoplasmic extracts were made by lysing FL cells in a hypotonic buffer with 0.1% NP-40 and pelleting nuclei at 6000g for 4 minutes. The supernatant solution was used as cytoplasmic extract. Nuclear proteins were extracted with 400 mM NaCl by rocking at 4°C for 20 minutes. Then, 15 to 30 µg protein from whole cell extracts or 5 to 10 µg nuclear or cytoplasmic protein was electrophoresed through a 10% SDS-polyacrylamide gel and transferred to an Immobilon-P membrane (Millipore, Bedford, MA) in tris-glycine buffer with 20% methanol. Membranes were probed with mAbs specific for Pbx1b and Pbx3a or for all 3 long isoforms of Pbx. After probing with HRP-conjugated anti-immunoglobulin (Ig) G mAb, complexes were detected by enhanced chemiluminescence (Amersham, Buckinghamshire, England).Fluorescence-activated cell sorting and analysis FLs were dissected from E14.5 embryos, drawn through a 25-gauge needle, and passed through fine mesh to generate a single-cell suspension. Erythrocytes were lysed in ammonium chloride potassium buffer. Cells were stained with phycoerythrin-conjugated anti-Fc R (2.4G2) fluorescein isothiocyanate (FITC)-conjugated CD34 (RAM34) (Pharmingen, San Diego, CA), Texas red-conjugated anti-Sca-1
(E13-161-7), allophycocyanin-conjugated anti-c-Kit (2B8), and
biotinylated mAbs specific for Ter119 and AA4.1. FL hematopoietic stem
cell (HSC) populations were stained and sorted as described by Morrison et al.18 For experiments requiring the sorting of HSCs or
myeloid progenitors, Ter119+ cells were partially removed
with sheep anti-rat IgG-conjugated magnetic beads (Dynabeads M-450)
(Dynal, Oslo, Norway), and the remaining cells were stained with
streptavidin-RED670 (Gibco BRL, Bethesda, MD). All cell populations
were sorted or analyzed by means of a highly modified triple-laser
(488-nm argon laser, 599-nm dye laser, and UV laser) FACS Vantage
(Becton Dickinson Immunocytometry Systems, Mountain View, CA).
Progenitors were purified by sorting and then re-sorting to obtain
precise numbers of cells that were essentially pure for the indicated
surface-marker phenotype. In single-cell clonogenic assays, the re-sort
was performed by means of a carefully calibrated automatic cell
deposition unit (ACDU) system (Becton Dickinson). This system deposited
a specific number of purified cells onto methylcellulose medium in
96-well plates.
Myeloid colony assays For colony-forming cell (CFC) assays, single-cell suspensions were prepared from E14 FL as described above. We mixed 20 000 cells from each liver in 1 mL 0.9% methylcellulose (Stem Cell Technologies, Vancouver, BC, Canada) in Iscoves modified Dulbecco medium supplemented with 20 ng/mL stem cell factor (SCF), 5 ng/mL granulocyte-macrophage colony-stimulating factor (GM-CSF) (R&D Systems, Minneapolis, MN), 5 ng/mL granuloctye CSF, and 5000 U/L erythropoeitin (Epo) (Amgen, Thousand Oaks, CA). Triplicate cultures from each FL sample (0.75 mL per well) were plated in 24-well plates. Colonies were counted after 7 days (3 days for erythroid colony forming units [CFU-E]) on the basis of standard morphological criteria. For clonal analysis of sorted myeloid progenitors, cells were cultured in an Iscove's-based methylcellulose medium (Methocult H4100) (Stem Cell Technologies) that was supplemented with 20% fetal bovine serum, 1% bovine serum albumin, 2 mM L-glutamine, 50 µM 2-mercaptoethanol, and 10% FL-conditioned medium. Cytokines such as mouse SCF (20 ng/mL) (R&D Systems), mouse interleukin-3 (IL-3; 30 ng/mL) (Genzyme, Cambridge, MA), mouse IL-11 (10 ng/mL) (R&D Systems), mouse GM-CSF (10 ng/mL), mouse thrombopoietin (10 ng/mL) (R&D Systems), mouse Flt-3 ligand (10 ng/mL) (R&D Systems), and human erythropoietin (1000 U/L) (R&D Systems) were added at the start of the culture. Colonies were enumerated under an inverted microscope consecutively from day 5 to day 12. Mixed colonies containing both erythroid and myelomonocytic cells (CFU-Mix) such as granulocyte, erythrocyte, megakaryocyte, macrophage
CFU; granulocyte, erythrocyte, megakaryocyte CFU; and granulocyte,
erythrocyte, megakaryocyte CFUwere determined by Giemsa
staining of cells that were picked from individual colonies by means of
fine drawn-out Pasteur pipettes. All cultures were incubated at 37°C
in a humidified chamber under 7% CO2.
Transplantation C57BL/6 mice were irradiated to 950 cGy from an X-ray source. For competitive reconstitution, 2.5 × 105 cells from Pbx1 / or Pbx1+/
cells were mixed with an equal number of cells from a normal C57BL/6K embryo and injected into the tail veins of irradiated recipients. The congenic strains of mice, C57BL/Ka-Thy1.1 (Ly5.1) and
C57BL/Ka-Thy1.1 (Ly5.2), were used as described by Kondo et al.19 For radioprotection and spleen CFU (CFU-S)
experiments, cells were administered to anesthetized recipients by
retro-orbital injection. Donor (Pbx1/) cell
contribution in long-term survivors of radioprotection experiments was
determined by Southern blot analysis by means of a probe (3') external
to the targeting construct on SspI-digested DNA isolated from whole
bone marrow cells.
Proliferation and apoptosis indices Pregnant mice resulting from Pbx1+/
intercrosses were injected retro-orbitally with bromodeoxyuridine
(BrdU) in 0.9% saline at 14 dpc. At 90 minutes after
injection, the mice were killed and the livers dissected from the
embryos. Common myeloid progenitors (CMPs) were sorted from FL-cell
suspensions as described above, and cytospin preparations from the
sorted progenitors were air-dried and fixed in methanol at  20°C for
BrdU staining or in a 1:1 mixture of methanol and acetone at room
temperature for proliferating cell nuclear antigen (PCNA) staining.
BrdU staining was performed with FITC-conjugated anti-BrdU (Becton
Dickinson, San Jose, CA) according to the manufacturer's
specification. Cells were counterstained with 4 µg/mL propidium
iodide. PCNA staining was performed as described by Hall et
al.20 Percentages were derived by counting 100 to 200 cells. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin end
labeling of fragmented DNA (TUNEL) assays were performed by means of an
in situ cell death detection kit (Boehringer Mannheim, Indianapolis,
IN) according to the manufacturer's recommendations.
Pbx1 is expressed in hematopoietic progenitors during embryonic hematopoiesis Pbx1 is expressed in the mesenchyme throughout the mid-gestation embryo.21 Its specific expression in the murine fetal hematopoietic compartments was examined here by immunostaining with highly specific mAbs developed in our laboratory.17 Strong nuclear staining for the Pbx1b, but not the Pbx1a, isoform was observed in the aorta-gonad-mesonephros (AGM), the earliest intra-embryonic site of hematopoiesis, at E11.5 (Figure 1A). This staining included cells that are enriched for hematopoietic progenitors in the mesonephric mesenchyme as well as occasional cells lining the dorsal aorta.22 At E14.5, Pbx1b+ cells were much less frequent in the FL than in the AGM, comprising primarily cells of the liver capsule, sinusoidal endothelium, and occasional intraparenchymal cells (Figure 1A). By Western blotting, expression of Pbx1b (38 kd) and Pbx3a (46 to 47 kd) was detected in extracts prepared from FL cells at E14.5 (Figure 1B). Both of these Pbx proteins were detected exclusively in the nuclear fraction (lanes 9 and 10). Three other Pbx proteins (Pbx1a, Pbx2, and Pbx3b) were not detected by Western blot in FL during this stage of hematopoietic differentiation (data not shown).
To identify the subsets of FL cells expressing Pbx1b and Pbx3a, cells
were purified on the basis of their surface phenotypes by means of
immunomagnetic enrichment and/or flourescence-activated cell
sorter (FACS). Ter119+ erythroid cells (Figure
1C), which compose approximately 70% of the FL population at E14.5,
expressed Pbx3a but not Pbx1b (Figure 1B). A population of cells
expressing the
lin Pbx1 deficiency results in severe fetal anemia Pbx1-deficient mice were created by gene targeting of the Pbx1 transcriptional unit whose disruption was shown to result in a null allele.40 As expected, no Pbx1 protein was detected by Western blot in Pbx1/ FL at E14.5 (Figure 1B, lane 2).
Pbx1+/ mice were born at the expected
Mendelian ratio, were fertile, and exhibited no gross abnormalities
except for significantly smaller size. Pbx1/
embryos, however, died between E15.5 and E16.5 and exhibited patterning
defects of the skeleton, severe hypoplasia of abdominal and thoracic
organs, and splenic aplasia.40 Among the most visually obvious features of Pbx1/ embryos were their
striking pallor and subcutaneous edema (Figure 2A). These features, which first became
evident at E12.5, were associated with profound anemia. While the size
and morphology of circulating erythrocytes did not differ significantly
between Pbx1/ and wild-type (wt) blood
(Figure 2B), mean hematocrits were 5% for
Pbx1/ embryos at E15.5, which contrasted
with 38% for Pbx1+/ and wt littermates
(Figure 3A). The approximately 8-fold
decrease in hematocrit reflected a similar reduction in the number of
circulating erythrocytes and is of a sufficient magnitude to contribute
to subcutaneous edema and death between E15.5 and
E16.5.25
Anemia in Pbx1 Definitive hematopoiesis initiates in Pbx1 /
embryos up to E16.5 exceeded the duration of significant numbers of yolk sac-derived erythrocytes. Moreover, examination of the peripheral blood of Pbx1/ embryos at E15.5
revealed substantial numbers of nonnucleated erythrocytes (Figure 2B)
likely to be of definitive origin. The proportion of residual nucleated
erythrocytes at E15.5 was not significantly higher in
Pbx1/ embryos than in their wt littermates
(Figure 3A). This suggested not only that primitive erythropoiesis was
spared by the absence of Pbx1, but that definitive erythropoiesis in
the FL was initiated at the expected stage of development. Accordingly,
myelomonocytic cells were always observed in FLs of
Pbx1/ embryos (not shown). Despite their
extreme pallor, no hemorrhages were observed in the skin, abdominal
cavity, or central nervous systems of Pbx1/
embryos, suggesting that platelet production was sufficient to prevent
spontaneous bleeding (Figure 2A and not shown).
Total myeloerythroid CFCs are reduced in
Pbx1 / embryos were reduced by 2- to 3-fold
(Figure 3C). Furthermore, enumeration of erythroid colonies after 3 days in methylcellulose cultures revealed a reduction in absolute
numbers of CFU-E per liver (4-fold) that was even more pronounced than
the decrease in other CFCs (Figure 3C). Addition of a 10-fold excess of
Epo to the culture medium did not alter these findings, suggesting that
insensitivity to Epo was not responsible for the decrease in CFU-E
growth. Culture of several thousand Ter119+ cells from wt
or Pbx1/ FL exhibited no colony-forming
potential (not shown), indicating that the observed reductions were
specific to progenitor populations that normally express Pbx1.
Pbx1 / FL, their phenotypic frequency was
examined at E14. Flow cytometry showed that the absolute numbers of
linSca-1+c-Kit+AA4.1+
cells that normally contain all of the multilineage long-term repopulating activity in FL were modestly decreased in
Pbx1/ embryos (Figure
4A), but this did not achieve statistical
significance (P = .07). Cells expressing this surface
phenotype were sorted individually into single wells containing
methylcellulose medium. In these assays,
Pbx1/ cells showed normal colony
distributions while displaying a slight decrease in the number of
colonies generated on a per-cell basis (Figure 4B).
To determine whether the in vivo clonogenic potential of
Pbx1 Pbx1 /
embryos or their heterozygous littermates (Ly5.1+) were
injected into lethally irradiated F1 mice created by
intercrossing strains expressing either of the codominant Ly5.1 or
Ly5.2 surface markers. An equal number of competitor FL cells
(Ly5.2+) from a normal E14 embryo were injected
simultaneously. Engraftment of recipient mice was monitored over time
by FACS analysis of peripheral blood cells for expression of Ly5
allotypes. The ratio of Ly5.1- to Ly5.2-derived cells was determined
after gating out residual recipient-derived Ly5.1/Ly5.2 double-positive
cells. In addition, the Ly5.1/Ly5.2 ratio was analyzed in specific
lineages by means of myeloid and lymphoid surface antigens. At the
earliest time point analyzed, Pbx1/-derived
peripheral blood cells were noticeably rarer than
Pbx1+/-derived cells (Figure
5A). By 4 months,
Pbx1+/-derived progenitors had engrafted and
were contributing to myeloid and lymphoid reconstitution equally with
wt progenitors, suggesting no heterozygous deficit in
Pbx1+/ HSCs as tested by this functional
assay. Pbx1/ progenitors, in contrast,
contributed to fewer than 2% of engrafted hematopoietic cells. Myeloid
and lymphoid lineages in the latter animals were derived almost
exclusively from the Ly5.2-expressing (ie,
Pbx1+/+) competitor cells (Figure 5B).
The autonomous reconstitution potential of
Pbx1 All of the radioprotected mice survived 6 months after transplantation,
allowing an evaluation of the long-term repopulating capacity of
Pbx1 Absolute and relative numbers of CMP are reduced in
Pbx1 / and wt FL were examined by flow
cytometry. In wt or Pbx1+/ FL, CMPs
(CD34+/FcRlo) composed approximately 1% of
whole FL cells (Figure 6A). In contrast,
Pbx1/ CMPs were substantially reduced in
frequency to approximately 0.4%, on average. This decrease in relative
numbers corresponded to an approximate 5-fold decrease in their
absolute numbers per Pbx1/ liver (Figure
6B). MEPs and GMPs were present at roughly normal relative frequencies
within Pbx1/ FL (Figure 6A). The absolute
numbers of MEPs and GMPs, however, were decreased approximately 2-fold
in direct proportion to the overall liver size (Figure 6B) and
paralleled reductions in erythroid and GM-CFCs (Figure 3C).
Absence of Pbx1 leads to deficiencies in the clonogenic potentials of CMPs and MEPs The erythroid colony-forming potentials of CMPs and MEPs were assayed since these subsets appear to be the major erythropoietic progenitors in FL.39 These progenitors, as well as GMPs, were enriched to greater than 99% purity by 2 successive rounds of flow cytometry, and cells were individually sorted into single wells containing methylcellulose media as described by Akashi et al.24 Even though sorted single Pbx1/ CMPs had normal overall plating
efficiency, they produced approximately 3-fold fewer erythroid,
megakaryocytic, and mixed erythroid/ megakaryocytic colonies than did
their wt counterparts (Figure 6C). The skewed in vitro differentiation
of Pbx1/ CMPs toward the myelomonocytic
pathway suggested that Pbx1 was required for the efficient production
of erythroid colonies. Furthermore, only 30% of
Pbx1/ MEPs produced a visible colony after 7 days in culture, as compared with 80% of wt MEPs (Figure 6C). The
colonies that were produced by Pbx1/ MEPs
were comparable in size to the wt MEP colonies and contained morphologically normal-appearing erythroid and megakaryocytic cells
(not shown). These data suggested that the reduced ability of
Pbx1/ MEPs and CMPs to produce
erythroid-committed progeny directly underlies the anemia in
Pbx1/ embryos. As expected, no
colony-forming activity was observed in the lin+ or
c-Kit fractions of whole FL (data not shown), indicating
that the observed reductions were not a consequence of altered cell
surface phenotypes in Pbx1/ progenitors.
Numerical decrease in Pbx1 / FL. Cytospin preparations of the
c-Kit+CD34+FcRlo populations
were fixed and stained for PCNA or used for TUNEL assays. The latter
showed that less than 5% of each progenitor population was apoptotic
and revealed no differences between wt and Pbx1/
progenitor populations (data not shown). Approximately 80% of CMPs from wt embryos exhibited nuclear PCNA staining (Figure
7), consistent with their high
proliferative index (D.T., unpublished results, 2000). In
contrast, only 20% to 25% of the Pbx1/
CMPs showed similar staining. Comparison of GMP and MEP populations stained for PCNA revealed no significant differences between
Pbx1/ and wt (not shown). To confirm these
results, in vivo BrdU-labeling studies were performed. Cytospin
preparations of flow-sorted CMPs stained for BrdU incorporation showed
reductions in S-phase cells that paralleled the decreased fraction of
Pbx1/ CMPs observed by PCNA staining (Figure
7). These data indicated that FL CMPs normally constitute a highly
proliferative subset and suggested that reduced cycling of
Pbx1/ CMPs probably contributed to their
proportionally decreased numbers within the progenitor compartment
at E14.
The studies in this report demonstrate that the Hox cofactor and
proto-oncoprotein Pbx1 is essential for the adequate maintenance of
definitive hematopoiesis. This role is consistent with our finding of
Pbx1 expression in pluripotent and lineage-restricted progenitors at
sites of embryonic hematopoiesis. Lack of Pbx1 expression in these
tissues results in FL hypoplasia and anemia, associated with lethality
in late gestation. Impaired function of Pbx1
The hematopoietic failure in Pbx1 The failure to adequately maintain definitive hematopoiesis in
Pbx1 An additive phenotype is consistent with the proposed role of Pbx1 as a
cofactor for multiple homeodomain proteins during hematopoietic
development. Accordingly, while mice deficient for individual
Hox genes such as HoxA9, HoxB6, or
HoxC8 exhibit some hematopoietic
abnormalities,14-16 the abnormalities are not as severe as
those we have described in Pbx1 While we observed defects in multiple subsets of
Pbx1 The substantial reduction in the proliferative index of
Pbx1
The authors thank Carmencita Nicholas and Eva Pfendt for expert technical assistance, Phil Verzola for photographic assistance, Ramesh A. Shivdasani for instruction in the determination of fetal hematocrits, Koichi Akashi for assistance with the ACDU, and Len Zon for critical review of the paper.
Submitted December 17, 2000; accepted April 2, 2001.
Supported by grants from the National Cancer Institute (CA70404, CA42971, and CA42551). J.F.D. was supported by Public Health Service grant 5T32-CA09151 awarded by the National Cancer Institute, and D.T. was supported by National Institute of Allergy and Infectious Diseases grant 5T32 AI-07290.
J.F.D., L.S., and D.T. contributed equally to this work.
The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked "advertisement" in accordance with 18 U.S.C. section 1734.
Reprints: Michael L. Cleary, Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305; e-mail: mcleary{at}stanford.edu.
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  J. T. Park, I.-M. Shih, and T.-L. Wang Identification of Pbx1, a Potential Oncogene, as a Notch3 Target Gene in Ovarian Cancer Cancer Res., November 1, 2008; 68(21): 8852 - 8860. [Abstract] [Full Text] [PDF]
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 U. D. Lichtenauer, M. Duchniewicz, M. Kolanczyk, A. Hoeflich, S. Hahner, T. Else, A. B. Bicknell, T. Zemojtel, N. R. Stallings, D. M. Schulte, et al. Pre-B-Cell Transcription Factor 1 and Steroidogenic Factor 1 Synergistically Regulate Adrenocortical Growth and Steroidogenesis Endocrinology, February 1, 2007; 148(2): 693 - 704. [Abstract] [Full Text] [PDF]
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H. Tanaka, I. Matsumura, K. Itoh, A. Hatsuyama, M. Shikamura, Y. Satoh, T. Heike, T. Nakahata, and Y. Kanakura HOX Decoy Peptide Enhances the Ex Vivo Expansion of Human Umbilical Cord Blood CD34+ Hematopoietic Stem Cells/Hematopoietic Progenitor Cells Stem Cells, November 1, 2006; 24(11): 2592 - 2602. [Abstract] [Full Text] [PDF]
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E. Ferretti, J. C. Villaescusa, P. Di Rosa, L. C. Fernandez-Diaz, E. Longobardi, R. Mazzieri, A. Miccio, N. Micali, L. Selleri, G. Ferrari, et al. Hypomorphic Mutation of the TALE Gene Prep1 (pKnox1) Causes a Major Reduction of Pbx and Meis Proteins and a Pleiotropic Embryonic Phenotype Mol. Cell. Biol., August 1, 2006; 26(15): 5650 - 5662. [Abstract] [Full Text] [PDF]
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D. Penkov, P. Di Rosa, L. Fernandez Diaz, V. Basso, E. Ferretti, F. Grassi, A. Mondino, and F. Blasi Involvement of Prep1 in the {alpha}{beta} T-Cell Receptor T-Lymphocytic Potential of Hematopoietic Precursors Mol. Cell. Biol., December 15, 2005; 25(24): 10768 - 10781. [Abstract] [Full Text] [PDF]
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A. Brendolan, E. Ferretti, V. Salsi, K. Moses, S. Quaggin, F. Blasi, M. L. Cleary, and L. Selleri A Pbx1-dependent genetic and transcriptional network regulates spleen ontogeny Development, July 1, 2005; 132(13): 3113 - 3126. [Abstract] [Full Text] [PDF]
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L. Selleri, J. DiMartino, J. van Deursen, A. Brendolan, M. Sanyal, E. Boon, T. Capellini, K. S. Smith, J. Rhee, H. Popperl, et al. The TALE Homeodomain Protein Pbx2 Is Not Essential for Development and Long-Term Survival Mol. Cell. Biol., June 15, 2004; 24(12): 5324 - 5331. [Abstract] [Full Text] [PDF]
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E. Longobardi and F. Blasi Overexpression of PREP-1 in F9 Teratocarcinoma Cells Leads to a Functionally Relevant Increase of PBX-2 by Preventing Its Degradation J. Biol. Chem., October 3, 2003; 278(40): 39235 - 39241. [Abstract] [Full Text] [PDF]
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Y. Okada, R. Nagai, T. Sato, E. Matsuura, T. Minami, I. Morita, and T. Doi Homeodomain proteins MEIS1 and PBXs regulate the lineage-specific transcription of the platelet factor 4 gene Blood, June 15, 2003; 101(12): 4748 - 4756. [Abstract] [Full Text] [PDF]
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J. M. Bjornsson, N. Larsson, A. C. M. Brun, M. Magnusson, E. Andersson, P. Lundstrom, J. Larsson, E. Repetowska, M. Ehinger, R. K. Humphries, et al. Reduced Proliferative Capacity of Hematopoietic Stem Cells Deficient in Hoxb3 and Hoxb4 Mol. Cell. Biol., June 1, 2003; 23(11): 3872 - 3883. [Abstract] [Full Text] [PDF]
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B. M. Owens and R. G. Hawley HOX and Non-HOX Homeobox Genes in Leukemic Hematopoiesis Stem Cells, September 1, 2002; 20(5): 364 - 379. [Abstract] [Full Text] [PDF]
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D. Traver, T. Miyamoto, J. Christensen, J. Iwasaki-Arai, K. Akashi, and I. L. Weissman Fetal liver myelopoiesis occurs through distinct, prospectively isolatable progenitor subsets Blood, August 1, 2001; 98(3): 627 - 635. [Abstract] [Full Text] [PDF]
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Top
Abstract
Introduction
-thalassemia in mice lacking the erythroid CACCC-transcription factor EKLF.
Nature.
1995;375:318-322