Genome-wide DNA methylation profiles in
hematopoietic stem and progenitor cells reveal
overrepresentation of ETS transcription factor
Amber Hogart,1Jens Lichtenberg,1Subramanian S. Ajay,2Stacie Anderson,1,3
NIH Intramural Sequencing Center,4Elliott H. Margulies,2and David M. Bodine1,5
1Genetics and Molecular Biology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda,
Maryland 20892, USA;2Genome Technology Branch, National Human Genome Research Institute, National Institutes of Health,
Bethesda, Maryland 20892, USA;3Flow Cytometry Core Facility, National Human Genome Research Institute, National Institutes
of Health, Bethesda, Maryland 20892, USA;4NIH Intramural Sequencing Center, National Human Genome Research Institute,
NIH, Rockville, Maryland 20852, USA
DNA methylation is an essential epigenetic mark that is required for normal development. Knockout of the DNA methyl-
transferase enzymes in the mouse hematopoietic compartment reveals that methylation is critical for hematopoietic differ-
entiation. To better understand the role of DNA methylation in hematopoiesis, we characterized genome-wide DNA
methylation in primary mouse hematopoietic stem cells (HSCs), common myeloid progenitors (CMPs), and erythroblasts
(ERYs). Methyl binding domain protein 2 (MBD) enrichment of DNA followed by massively parallel sequencing (MBD-seq)
was used to map genome-wide DNA methylation. Globally, DNA methylation was most abundant in HSCs, with a 40%
reduction in CMPs, and a 67% reduction in ERYs. Only 3% of peaks arise during differentiation, demonstrating a genome-
wide decline in DNA methylation during erythroid development. Analysis of genomic features revealed that 98% of pro-
moter CpG islands are hypomethylated, while 20%–25% of non-promoter CpG islands are methylated. Proximal promoter
sequences of expressed genes are hypomethylated in all cell types, while gene body methylation positively correlates with
gene expression in HSCs and CMPs. Elevated genome-wide DNA methylation in HSCs and the positive association between
methylation and gene expression demonstrates that DNA methylation is a mark of cellular plasticity in HSCs. Using de novo
motif discovery, we identified overrepresented transcription factorconsensus binding motifs in methylatedsequences. Motifs
for several ETS transcription factors, including GABPA and ELF1, are overrepresented in methylated regions. Our genome-
wide survey demonstrates that DNA methylation is markedly altered during myeloid differentiation and identifies critical
regions of the genome and transcription factor programs that contribute to hematopoiesis.
[Supplemental material is available for this article.]
Epigenetic mechanisms of gene regulation are heritable, reversible
modifications that are critical for the organization of chromatin
and regulation of tissue-specific gene expression. DNA methyla-
tion is a dynamic epigenetic mark primarily localized to cytosine
residues in the context of a CpG dinucleotide in mammals. Tar-
geted disruption of the genes responsible for de novo methylation
and maintenance of DNA methylation during replication dem-
in the mouse (Laget et al. 2010; Ma et al. 2010). While the critical
role for DNA methylation in early development is clearly estab-
lished, the role for DNA methylation in tissue specification is less
DNA methylation has long been recognized as an important
mark in establishing and maintaining imprinted gene expression
and X-chromosome inactivation. Apart from these specialized
roles for DNA methylation, little is known about how DNA
methylation leads to more general alterations in gene expression.
Methyl-binding domain proteins are a family of DNA-binding
proteins that recognize methylated DNA and modify gene ex-
pression by forming complexes with other regulatory proteins.
Studies of mouse knockout models of the MBD proteins demon-
strate unique but nonessential roles for most of these proteins
(Bogdanovic and Veenstra 2009). Of the MBD proteins, MBD2
appears to play an important role in hematopoiesis, with specific
roles in globin gene switching (Rupon et al. 2006).
The hematopoietic system is ideal for the study of methyla-
tion during differentiation because primary cells at specific stages
The hematopoietic stem cell (HSC) gives rise to all cells in the pe-
ripheral blood. The common myeloid progenitor (CMP) generates
only myeloid cells (red cells, platelets, granulocytes, monocytes,
and eosinophils), but not lymphoid cells (T- and B-lymphocytes).
Erythroblasts (ERYs) are nucleated red blood cells that have com-
mitted to terminal differentiation. Conditional knockout mice in
which the genes for the de novo methyltransferases Dnmt3a and
Dnmt3b are deleted in HSCs retain the ability to differentiate into
both myeloid and lymphoid lineages, but long-term repopulation
of the hematopoietic system is impaired (Tadokoro et al. 2007).
Serial transplantation of Dnmt3a deficient HSCs revealed impaired
Article published online before print. Article, supplemental material, and pub-
lication date are at http://www.genome.org/cgi/doi/10.1101/gr.132878.111.
22:1407–1418 ? 2012, Published by Cold Spring Harbor Laboratory Press; ISSN 1088-9051/12; www.genome.org
differentiation as well as impaired repopulation (Challen et al.
2012). Similarly, conditional knockout mice in which the gene
for the maintenance DNA methyltransferase Dnmt1 is deleted in
HSCs demonstrated severe impairment of repopulating ability
and inappropriate enhancement of mature myeloid lineages
(Broske et al. 2009; Trowbridge et al. 2009). Together these
studies demonstrate a profound role for DNA methylation in
While the importance of DNA methylation in hematopoietic
differentiation has been well established, the genome-wide local-
ization of methylated DNA at specific stages of myeloid differen-
tiation remains to be elucidated. Recent advances in sequencing
technology have allowed comprehensive surveys of DNA meth-
ylation with varying degrees of resolution. The highest-resolution
techniques use bisulfite sequencing approaches that have the ad-
vantage of single-base resolution but do not distinguish between
5-methylcytosine and 5-hydroxymethylcytosine (Kriaucionis and
Heintz 2009; Tahiliani et al. 2009). In this study, we used a recombi-
nant methyl-binding domain protein to enrich 5-methylcytosine
modified regions of the genome for massively parallel sequence
analysis (MBD-seq). Using this approach, we compared genome-
wide methylation in purified populations of murine HSCs, CMPs,
and ERYs. By focusing on methylation changes defined by peaks
as opposed to site-specific methylation, we were able to identify
discrete regions of the genome where dynamic methylation
changes occur during hematopoiesis. Our study reveals that the
greatest number of methylation peaks occurs in HSCs and that
these peaks are specifically and successively lost during myeloid
differentiation, consistent with the bias in myeloid lineages seen
in Dnmt1 knockout mice (Broske et al. 2009; Trowbridge et al.
2009). The identification of regions where methylation changes
during hematopoiesis will facilitate mechanistic studies of how
DNA methylation regulates hematopoietic differentiation.
Genome-wide DNA methylation declines during myeloid
Whole-genome sequencing in human embryonic stem cells has
demonstrated that as much as 80% of all CpG dinucleotides in the
genome are methylated (Laurent et al. 2010), yet it is unlikely that
all of these sites are relevant to differentiation. MBD-seq identifies
regions of the genome bound by a DNA methylation-binding
protein, highlighting loci containing multiple methylated CpG
sites. Recombinant MBD2 pull-down of methylated genomic DNA
combined with massively parallel sequencing was used to identify
methylated genomic loci in enriched populations of lineage neg-
ative Sca1+c-kit+cells (a population of cells enriched for long- and
short-term HSCs and multipotent progenitors, which we have
designated as HSCs), common myeloid progenitors (CMPs), and
erythroblasts (ERYs) (Fig. 1A). Two biological replicates were in-
cluded for each of the three cell types with the total number of
reads ranging from 32 to 46 million. A complete summary of the
sequencing reads is provided in Supplemental Table S1. Non-
enriched genomic DNA was sequenced to determine a standard
background for subsequent analysis. Supplemental Figure S2 il-
lustrates the sequencing results for a region containing the im-
printing control region of the imprinted gene Snrpn. Consistent
with the observation that Snrpn is imprinted within all cells,
specific peaks of DNA methylation were detected in all three cell
To quantify genome-wide DNA methylation levels, mapped
sequencing reads were analyzed to determine statistically signifi-
cant peaks of methylation. In a conservative filtering approach,
MBD-seq peaks were called if they were present in both biological
replicates and overlapped by at least 200 bp. The average distri-
bution of peak lengths was also investigated, with the average
peaks occupying slightly more than 800 bp in each cell type
(Supplemental Table S2). Comparison of overall peak count from
each cell type revealed that DNA methylation peaks were most
abundant in HSCs (85,797), with decreasing levels in CMPs
(50,638) and fewer in ERYs (27,839) (Fig. 1B). The decrease in
methylation reflects a global genomic decrease that is demon-
strated by the similar relative distribution of methylation peaks on
each chromosome between cell types despite the reduction in the
total number of methylation peaks (Fig. 1C). Among the auto-
somes, chromosome 5 has the greatest number of DNA methyla-
tion peaks in all cell types, while the fewest number of peaks was
found on chromosome 19. The X chromosome is subject to ran-
dom X-chromosome inactivation in females, a process associated
CMP data sets were female, the fetal tissues used for ERY also
included males resulting in a slightly lower density of peaks on the
X chromosome in ERYs.
Both in silico validation of CpG content within peaks as well
that the MBD-seq approach specifically recognizes methylated
DNA. The distribution of peak length is shown in Supplemental
TableS2, andthedistributionofCpGcontentis shownin TableS3.
At least 99.96% of all peaks called contained one CpG site with the
average CpG count ranging from 21 to 24 CpGs per peak (Sup-
plemental Table S3). Random sampling of sequences of similar
length revealed that the MBD-enrichment approach results in a
statistically significant higher percentage of peaks with CpG sites
than is expected by chance (P-value = 0.00507) and with a signifi-
cantly higher average CG content (P-value = 0.00391). Bisulfite
sequencing of 10 genomic loci containing MBD-seq peaks (five com-
mon to all three data sets, four peaks unique to HSCs or progenitors
sentation of hematopoiesis highlighting the three cell types enriched for
methylation analysis. HSC and CMP cell populations were lineage de-
pleted (Lin?) and then positively selected with the cell surface markers
Sca1 and c-kit. Erythroblast cells were positively selected with antibodies
forTer119 andCD71. (B) Total number of methylation peaks called in each
of the three cell populations. (C) Total methylation peak count per chro-
mosome for each cell population: HSC (blue); CMP (orange); ERY (red).
Overview of MBD sequencing results. (A) Schematic repre-
1408 Genome Research
Hogart et al.
[HSCs + CMPs], and one peak unique to ERYs) were found to have
at least 47% methylation at the CpG sites per region investigated
with an average of ;80% methylation (Supplemental Fig. S5;
Supplemental Table S4). Bisulfite sequencing at genomic regions
average of 30.7% methylated CpG sites, consistent with the ob-
servation that CpG methylation is relatively common throughout
the genome. The presence of low-to-intermediate levels of meth-
ylation in regions excluded from peaks confirms that the MBD-seq
approach identifies regions of the genome with high-density
methylation.An additionalvalidation ofour MBD-seqdatasetwas
achieved by comparing our methylation peaks to the recently
published (Shearstone et al. 2011) reduced representation bisulfite
sequencing (RRBS) data from mouse erythroblasts. Supplemental
Figure S6 shows the degree of overlap between the erythroblast
MBD-seq peaks and the RRBS data. Consistent with the conven-
40% methylation (Supplemental Fig. S6).
Because global DNA methylation peaks decrease with mye-
loid differentiation, we determined whether methylation peaks
were shared among the cell types or whether the peaks were
unique to each of the three cell types. Seven categories of DNA
methylation peaks based on presence in one or more cell types are
shown in Figure2. Thelargestcategory of DNAmethylation peaks,
composing nearly 40% of all peaks, were unique to HSCs. Meth-
ylation peaks common to all three cell types were the next largest
category, representing 28% of all methylation peaks. The third
ERYs (progenitor ;27%). Approximately 3% of the total methyl-
ation peaks were unique to either ERYs or CMPs, and an even
smallerfractionof peaks(0.3%)were absentin HSCsbutpresentin
the more differentiated cell types (myeloid). Figure 3A demon-
strates examples of HSCs and progenitor-specific methylation
peaks upstream of the important hematopoietic transcription
factor gene Gata2. An example of an ERY-specific peak in the Meis1
locus is shown in Figure 3B. Overall, the distribution of peaks
within each of the cell types demonstrates a progressive global de-
new methylation peaks during the later stages of differentiation.
DNA methylation is overrepresented in the coding portion
of the genome
We next investigated the genomic distribution of methylation
peaks. The genome was divided into five partitions defined by
RefSeq genes. The proximal promoter was defined as sequences
1 kb upstream of the transcription start site (TSS) through the first
50 bp past the transcriptional start site. Gene body methylation
was defined by the RefSeq gene coordinates minus the first 50 bp
of and downstream from gene boundaries because we expected
these flanking sequences to also contain cis regulatory elements.
The remainder of the genome constitutes the intergenic partition.
The distribution of methylation peaks in each cell-type category
was compared with the relative percentage of sequence in each
partition to the total nonrepetitive portion of the genome (geno-
mic average). Significant deviation from the expected distribution
was observed for common peaks and for peaks in all multipotent
categories (Table 1). An overrepresentation of methylation peaks
was seen in the RefSeq portion of the genome, and methylation
peaks were overrepresented in the downstream flanking regions
and were similar to the expected percentage in both the distal
promoter and 59-flanking regions in all peak categories.
portion of the genome. The RefSeq sequences were divided into four
categories: 59-untranslated sequences (8.7%), 39-untranslated se-
quences (6.8%), exons(5.3%), and introns(79.2%). Althoughexons
represent ;5% of the gene sequence, methylation peaks were sig-
nificantly overrepresented in the exons (7%–25% of all the genic
DNA methylation peaks) (Table1) and underrepresented in the in-
trons in most categories. Since the number of potential methylation
contribution of CpG dinucleotides in each partition and compared
this with peak distributions. Table 2 demonstrates that MBD-seq
peak density doesnot followCpGdistribution, because methylation
peaks exceed the relative contribution of CG in both exons and in-
trons, while methylation peaks are found at less than the expected
frequency in both the 59 and 39 UTR compartments (Table 2).
CpG island methylation is rare in hematopoietic stem
Previous studies have shown that CpG islands in characterized
promoters of genes remain unmethylated in most instances, while
CpG islands not associated with known promoters, orphan CpG
islands, are much more likely to be methylated (Illingworth et al.
2010). Consistent with a previous report of methylated CpG islands
in whole mouse blood (Illingworth et al. 2010), we found ;2% of
diagram illustrating the degree of overlap in methylation peaks between
cellpopulations. (B)Totalpeakcount foreachcell population, thenumber
of peaks shared between each cell type, and the percentage that each
category contributes to the total number. Progenitor peaks are defined as
present in HSCs and CMPs but absent in ERYs. Myeloid peaks are absent in
HSCs but present in CMPs and ERYs. (Other) Peaks that were absent in the
CMP but present in HSCs and ERYs.
Analysis of peak sharing between cell populations. (A) Venn
Genome-wide DNA methylation in hematopoiesis
promoter CpG islands methylated in HSCs, and a smaller percent
methylated in the more differentiated hematopoietic cell types
(Fig. 4A). Orphan CpG islands were around 10-fold more likely to
be methylated in each of the cell types, consistent with the greater
role in tissue-specific methylation.
Investigation of cell-type-specific methylation peaks revealed
that the vast majority of all promoterCpG islands are unmethylated
in all categories. Increased promoter-associated methylation observed
in the progenitor category (HSCs + CMPs) compared with com-
mon and HSC-specific promoters (Fig. 4B). In contrast, the meth-
ylation of orphan CpG islands varied between peak-type cate-
gories. The largest percentage of methylated orphan CpG islands
was among the common methylation peaks (20%) (Fig. 4B). Al-
though HSC is the most methylated cell type, the percentage of
less than common peaks and around threefold lower than the
sequencing data for each cell population: blue (HSC), orange (CMP), and red (ERY), with significant peaks shown as black bars below each sample. The
y-axis indicates peak height, defined by the maximum number of sequencing tags seen in the highest visible peak in each window. Transcription factor
consensus sites (TRANSFAC IDs) are indicated above the MBD-seq data in regions of significant peaks. The gene structure is indicated below the MBD-seq
data with CpG islands shown in green. Bisulfite sequencing data confirming the cell-type-specific methylation are shown below. (Black circles) Methylated
CpG sites; (open circles) unmethylated CpG sites. Each horizontal line indicates a unique clone.
MBD-seq peaks at selected loci. UCSC Genome Browser view of the Gata2 locus on Chr6 (A) and the Meis1 locus on Chr11 (B). Raw
Hogart et al.
1410 Genome Research
progenitor category (Fig. 4B). These results suggest that the re-
quirement of DNA methylation for maintenance of HSCs is not
primarily due to silencing of genes via methylated CpG islands.
DNA methylation in expressed genes varies
by genomic partition
To investigate the role that DNA methylation plays in gene ex-
pression, we compared the genomic distribution of DNA methyl-
ation peaks to gene expression data obtained from BloodExpress,
a database containing gene expression profiles from a large num-
ber of mouse hematopoietic cell types (Miranda-Saavedra et al.
2009). Based ongene expressionprofilesformouse HSC,CMP, and
ERY cell types, the greatest number of genes is expressed in the
HSCs (8594), followed by CMPs (7122), and the fewest number of
expressed genes are seen in ERYs (4223). Peaks assigned to the
upstream 10 kb, proximal promoter, RefSeq gene boundary, and
downstream 10 kb were compared in expressed genes. Consistent
with the observations of Hodges et al. (2011), the majority of
expressed genes lacked methylation peaks in the proximal pro-
moter, with a similar trend seen in the more upstream 10 kb
(Fig. 5A,B). In contrast, the majority of expressed genes in HSCs
and CMPs contained methylation peaks within the gene body
(RefSeq) (Fig. 5A). Methylation peaks were also investigated in
genes that were not expressed in each cell type. Consistent with
the larger absolute number of nonexpressed genes, the number of
methylated nonexpressed genes exceeds the number of methyl-
ated expressed genes for each partition (Supplemental Fig. S7).
While the ratio of unexpressed methylated genes to expressed
methylated genes is similar between the upstream, downstream,
and RefSeq partitions, this ratio is elevated in the proximal pro-
moter for each cell type and markedly elevated in ERYs. These data
further supporttherolethat proximalpromotermethylationplays
in gene silencing.
On average, genes had multiple methylation peaks, with the
2.7 peaks in CMPs, and 2.1 peaks in ERYs. We investigated the
association of methylation peaks in multiple genomic partitions
simultaneously to ascertain if specific patterns were associated
with positive gene expression. Figure 5C shows the percentage of
expressed genes with methylationpeaks in two or more of the four
partitions: upstream 10 kb (UP), proximal promoter (PP), RefSeq
gene boundaries (CDS), and 10 kb downstream (DS). Consistent
with the single partition analysis, expressed genes are unlikely to
have methylation in the proximal promoter in combination with
any other genomic region. Of the two-partition correlations,
methylation most frequently occurred together in the gene bodies
(CDS) and the 10 kb downstream (DS) partitions, in each of the
cell types, with the minimal two-partition correlation occurring in
the proximal promoter and the downstream partitions (Fig. 5C).
Further analysis of genes with methylation in three or more par-
titions revealed that 10-fold more expressed genes had methyla-
tion in the gene body and flanking regions than in all four parti-
tions in each of the three cell types. Therefore, while proximal
promoter methylation is rare in expressed genes, methylation in the
gene body and flanking regions outside of the proximal promoter
occurs often in expressed genes.
De novo motif discovery reveals differentially methylated
transcription factor binding site signatures of hematopoietic
To elucidate developmental programs potentially modified by the
presence of DNA methylation, we investigated the sequences un-
derneath the methylation peaks for recurring motifs. De novo
motif discovery was performed on all data sets and genomic par-
titions independently. The top 25 overrepresented motifs were
queried against the TRANSFAC (Matys et al. 2006) transcription
factor database,and transcription factors with characterizedbinding
sites were identified. Figure 6 contains a summary of the tran-
scription factors with overrepresented motifs occurring at sites of
DNA methylation within the five genomic partitions (identified
highlights transcription factors that occurin only one peak category
(red) such as MATH1 in HSC proximal promoter peaks, two cate-
gories (green), three categories (teal), and transcription factors that
are overrepresented in almost all data sets (dark blue) such as
Comparison of the overrepresented transcription factor
binding sites revealed that >10% of all overrepresented motifs
corresponded to ETS transcription factors. Although the ETS
transcription factor (ELF1, ETS2, FLI1, and GABPA) binding
sites were overrepresented in all five genomic partitions, the
distribution within cell-type-specific categories was quite dif-
ferent. Common methylation peaks had overrepresentation of
all ETS factors in all partitions except in the intergenic partition.
In contrast, HSC-unique peaks lacked overrepresentation of
GABPA in the promoter and flanking partitions but exhibited
Distribution of methylation peaks in genomic partitions (% in partition)
promoterRefSeq59 UTRExonIntron39 UTR Downstream IntergenicP-value
1.61303 3 10?18
7.02049 3 10?05
Peak partition distribution within genes compared with
59 UTR Exon Intron39 UTRP-value
% of total CG
5.80995 3 10?17
1.94352 3 10?12
1.48518 3 10?11
7.10713 3 10?12
1.51578 3 10?13
1.09267 3 10?13
Genome-wide DNA methylation in hematopoiesis
overrepresentation of multiple ETS sites within the intergenic par-
tition. These complementary patterns of transcription factor motifs
suggest that DNA methylation may modulate ETS transcription
factor occupancy during hematopoietic
Other transcription factor motifs
such as the NFAT (nuclear factor of acti-
vated T-cells) were highlyspecifictosingle
site is overrepresented in CMP-unique
methylation and myeloid-specific peaks
located in the proximal promoter. The
NFAT2 motif is overrepresented in CMP-
unique methylation peaks located in the
proximal promoter and downstream re-
gions, and in the distal promoter of my-
eloid peaks. In contrast, the NFAT3 motif
is overrepresented in common and pro-
genitor methylation peaks located in the
proximal promoter. The striking differ-
ence between overrepresented motifs in
cell-type-specific methylation profiles
demonstrates that hematopoietic line-
ages contain unique signatures of methyl-
ation patterns that may regulate changes
that occur during differentiation.
Minimal genome-wide co-occupancy
of hematopoietic transcription factors
with DNA methylation peaks
To assess the relationship between ge-
nome-wide DNA methylation and tran-
scription factor binding, we compared
our methylation data with genome-wide
occupancy data for a set of 10 key hema-
topoietic transcription factors (Wilson
et al. 2010). Transcription factor binding
in Wilson et al. was ascertained in the
immortalized HPC-7 mouse hematopoi-
etic cell line, a multipotent cell that can be differentiated into
various myeloid lineages (Pinto do O´et al. 1998). Overlap between
transcription factor peaks and MBD-seq peaks in CMPs and HSCs
are shown in Table 3. The genomic coverage of each transcription
factor data set and methylation peak data set was used to generate
random data sets to calculatethe expected genomicoverlaps based
on chance. A significant underrepresentation of overlap between
transcription factor sites and methylation peaks occurred in both
CMPs and HSCs (Table 3). The only transcription factor with
significant co-occurrence with methylation was FLI1 in HSC
methylation peaks. Of the 10 key hematopoietic transcrip-
tion factors included in the study by Wilson et al. (2010), FLI1
is the only factor with an annotated consensus site that was
overrepresented in our DNA methylation peaks.
Chromatin immunoprecipitation of FLI1 and ELF1 reveals
co-occupancy of transcription factors and methylation
To further investigate the relationship between DNA methylation
and transcription factor binding, we next identified the presence
of CpG sites in the overrepresented transcription factor motifs.
Table 4 contains a list of all transcription factors with known
binding sites that were overrepresented in our analysis of the
proximal promoter partition. Of the 19 transcription factor motifs
associated with sequences overrepresented in methylated proximal
peaks in the three cell types compared with the complete genomic CpG
islands classified by Illingworth et al. (2010). The percent of methylated
promoter CpG islands (blue) or orphan (non-promoter) CpG islands (red)
is shown for each cell type. (B) Methylated promoter and orphan CpG
islands in common and cell-type-specific peaks, as a percentage of total
Overlap of MBD-seq peaks with CpG islands. (A) MBD-seq
BloodExpress (Miranda-Saavedraetal.2009)geneexpression databaseforeachcelltypeandcompared
with MBD-seq peaks. (A) The number of expressed genes (y-axis) in each cell type with methylation
peaks in the distal promoter, proximal promoter, RefSeq gene body, and downstream region. (B) The
type. (C) Combinatorial analysis of methylation peaks occurring in all four genic partitions in expressed
genes. (UP) Upstream 10 kb; (PP) proximal promoter; (CDS) RefSeq gene boundary; (DS) downstream.
The presence (+) or absence (?) of methylation in the indicated partition is shown below the x-axis. The
y-axis shows the percentage of expressed genes with each methylation pattern.
Methylation in genic partitions of expressed genes. Gene expression was obtained from the
Hogart et al.
1412 Genome Research
promoters, five contained CpG sites within the consensus rec-
ognition sequence, and five contained a CpG dinucleotide im-
mediately adjacent to the binding sequence. Many consensus
binding sites in our data set lack CpG sites; therefore, it is un-
clear if methylation directly impacts binding of the transcription
To test the hypothesis that differential methylation directly
impacts the binding of transcription fac-
tors revealed by our de novo motif dis-
covery, we performed chromatin immu-
noprecipitation of the ETS factors ELF1
and FLI1. Methylation peaks primarily
localized to promoter regions of 10 dis-
tinct genes, as well as several genic peaks
were selected for validation. ELF1 and
FLI1 occupancy was compared in these
regions of differential methylation in
chromatin from CMPs and ERYs. Figure
7A shows the data for the endoglin (Eng)
elements have been identified (Pimanda
et al. 2006, 2008). Consistent with pro-
moter methylation corresponding to
gene silencing, this gene is unmethylated
and expressed in CMPs, and uniquely
methylated and silenced in ERYs, as
determined by BloodExpress (Miranda-
Saavedra et al. 2009). Although silenced,
FLI1 and ELF1 was observed in the ERY
promoter methylation peak (Fig. 7B,C).
differentially methylated sites were observed in two intronic peaks
of Eng. The methylation peak in the first intron (site 2) does not
overlap a functional conserved element, while the methylation
peak in intron 11 (site 3) corresponds to a conserved element that
has not been assayed for function. In both cases, the more meth-
ylated site was occupied by FLI1 and ELF1 (Fig. 7B,C). Overall, we
found that four of six regions with statistically significant differ-
ences in transcription factor occupancy showed increased binding
in the methylated cell type, while two of six regions had signifi-
cantly more binding in the less methylated cell type (Fig. 7B,C;
Supplemental Fig. S8). We conclude that methylation does not
prevent the binding of ELF1 or FLI1.
led to breakthroughs in genomics, especially in the area of epige-
netic control of gene regulation. A variety of approaches have been
developed to map DNA methylation including whole-genome
bisulfite sequencing (MethylC-seq), reduced representation bi-
sulfite sequencing (RRBS), and the enrichment-based sequencing
methods MeDIP-seq and MBD-seq. MethylC-seq requires more
sequencing reads (503) than enrichment approaches to yield
a comparable level of genome coverage, but provides single-
nucleotide resolution (Harris et al. 2010). Reduced representation
bisulfite sequencing provides an alternative to whole-genome bi-
sulfite sequencing; however, it provides high-resolution data for
only a limited portion of the genome (Meissner et al. 2005). The
enrichment approaches detect methylatedDNA fragments genome-
wide and assume methylation of nearby CpG sites. Comprehensive
comparison of the genome-wide method of MethylC-seq to the
MBD-seq and MeDIP-seq enrichment methods revealed a >97%
concordance rate for methylation calls throughout the genome
(Harris et al. 2010). We conclude that the MBD-seq is an accurate
and cost-effective approach to survey genome-wide DNA methyl-
ation in small numbers of primary cells. In this study, we used
MBD-seq combined with peak calling algorithms to describe DNA
binding motifs. The top 25 overrepresented sequence motifs for each
peak category and each genomic partition are compiled into a heatmap.
(Top) Transcription factors (TRANSFAC IDs) with confirmed consensus
sequences. (Right) Each genomic partition with cell-type categories. (Red
boxes) Transcription factor binding sites that are unique to one cell-
categories, teal boxes represent three categories, and blue boxes indicate
presence in three or more cell-type specific categories. Gray indicates that
the transcription factor is not overrepresented in the data set.
Heatmap of overrepresented methylated transcription factor
Overlap between transcription factor occupancy and methylation peaks
Methylation CMP (50,639)
2.16 3 10?96
3.70 3 10?101
2.81 3 10?23
1.23 3 10?28
5.81 3 10?49
7.98 3 10?18
2.86 3 10?29
9.91 3 10?14
5.61 3 10?29
7.42 3 10?35
Methylation HSC (85,797)
2.20 3 10?197
5.87 3 10?31
1.48 3 10?54
7.17 3 10?75
6.60 3 10?31
1.19 3 10?44
3.74 3 10?49
8.20 3 10?38
7.36 3 10?64
Genome-wide DNA methylation in hematopoiesis
methylation. Direct comparison of our MBD-seq data with the
reduced representation bisulfite sequencing (RRBS) data in pri-
mary mouse erythroblasts demonstrated that our MBD-seq peaks
are biased toward genomic regions with >30%–40% CpG methyl-
ation (Supplemental Fig. S6).
In mouse hematopoietic cells, we found 2%–3% methylated
promoter CpG islands in all cell types, consistent with MBD-seq
and MeDIP-seq studies in other mouse and human tissues (Weber
et al. 2007; Illingworth et al. 2010). Although only a few percent of
promoter CpG islands are methylated, CpG islands within genes
are more likely to be methylated in a tissue-specific manner
(Maunakea et al. 2010), and in our study, we identified that 20% of
non-promoter CpG islands were methylated in all hematopoietic
cells. Differential methylation of CpG islands, both promoter and
non-promoter, was less common in cell-type-specific peaks. This
observation is in agreement with the study recently published by
Deaton et al. (2011) in which differential methylation of CpG is-
lands between differentiated lymphoid cells was much less pro-
found than the differences observed between lymphoid cells and
brain cells. Our results are consistent with the hypothesis that
differential methylation at CpG islands
is more important for early stages of line-
age specification than for final cell fate
A comparison of DNA methylation
in pluripotent embryonic stem cells and
strated a positive association between
global DNA methylation levels and the
ability to differentiate into multiple cell
types (Lister et al. 2009; Laurent et al.
2010). Similar to what we have observed
in hematopoietic stem cells, studies of
embryonic stem cells have shown that
methylation is not restricted to tran-
expressed genes in stem cells contain
DNA methylation within the gene body
(Lister et al. 2009; Laurent et al. 2010).
Additionally, the correlation between
DNA methylation and the repressive his-
tone modification H3K27me3 is not ob-
served in pluripotent embryonic stem
cells (Laurent et al. 2010). These findings
suggest that DNA methylation in stem
cells is not directly involved in in-
activation of genes, but may instead be
a mark enabling genomic plasticity. Our
demonstrating high levels of methyla-
tion in the multipotent hematopoietic
stem cell with progressive loss of meth-
ylation during erythroid specification
supports the positive role for DNA
methylation in cellular plasticity.
DNA methylation dramatically de-
creases as differentiation proceeds from
hematopoietic stem cells to lineage-re-
and the terminally committed erythro-
blast. These data are consistent with the
observations of Shearstone et al. (2011),
whohave alsodemonstrated global demethylation in terminally
differentiating erythroid cells. These genome-wide profiles
methylation in primary lymphoid (B- and T-) cells (Ji et al. 2010;
Deaton et al. 2011; Shearstone et al. 2011). Ji et al. (2010) used an
array-based method to investigate methylation at ;4.6 million
multipotent progenitor cells, CMPs, lymphoid progenitors, and
differentiated T-cells. In contrast to the decreasing global DNA
methylation we observed in differentiating myeloid and erythroid
cells, both Ji et al. (2010) and Deaton et al. (2011) found little
difference in the methylation of primitive and mature lymphoid
cells. We conclude that methylation alterations play a much larger
role in the differentiation of myeloid and erythroid cells than in
the differentiation of lymphocytes. This conclusion is supported
by the observation that mice deficient in Dnmt1 have increased
production of myeloid and erythroid cells (Broske et al. 2009;
Trowbridge et al. 2009).
We observed that regions of DNA methylation were
overrepresented for ETS transcription factor binding sites and that
Overrepresented motifs in proximal promoter
Transcription factorTRANSFAC binding siteIdentified motifCpG proximity
CpG within binding site
GABPALPHA (GABPA) CpG immediately adjacent
IK CpG within 1 bp
KAISO (ZBTB33) CTCCTGC
NFAT1 (NFATC2) ggaaag
CpG 2+ bp
Where different from TRANSFAC IDs, Mouse Genome Informatics-approved symbols are listed in
Hogart et al.
there was less than expected overlap between methylation peaks
and transcription factor occupancy. The ETS transcription factors
are required for both the maintenance of hematopoietic stem cells
and for myeloid development (Yang et al. 2011; Yu et al. 2011).
While typicallyviewedasactivatorsoftranscription, severalrecent
studies have characterized repressive functions of ETS factors
(Dryden et al. 2012; Lee et al. 2012), suggesting that modulation of
the binding of these factors may have complex effects on gene
expression. Our negative correlation between methylation peaks
and global transcription factor binding suggests that methylation
negatively impacts the binding of these transcription factors.
Alternatively, the lack of co-occurrence of methylation and tran-
factors binding primarily in methylation-deficient regions such as
promoters. Our chromatin immunoprecipitation analysis of FLI1
and ELF1 binding in promoters of multiple genes with differential
methylation peaks in CMPs and ERYs demonstrated that the more
methylated cell type often exhibited significantly enriched bind-
ing, which indicates that neither interpretation is entirely correct.
Since our methylation peaks span regions of several hundred base
pairs, we do not know whether the exact nucleotides bound by
transcription factors are methylated. Despite these limitations, we
conclude that methylated regions may be important for differen-
tial regulation of genes by transcription factors.
While genomic methylation is most reduced in erythroblasts,
some functionally important sites of methylation are retained,
including the imprinted loci Snrpn (Supplemental Fig. S2) and H19
as CKROX, a factor important for specification of CD4 T-cells
(Sun et al. 2005), and the ETS transcrip-
tion factor ELF1 were overrepresented
in the relatively rare erythroblast-unique
methylation peaks. We studied two genes
that are silenced in erythroid cells, Meis1
and Eng, which have erythroid-specific
methylation peaks that contain consen-
sus sites for ELF1, and both of these sites
are bound by ELF1 in erythroblasts. Al-
though ELF1 has not yet been reported to
function as a transcriptional repressor,
the redundant binding of ETS factors
(Hollenhorst et al. 2007; Okada et al.
2011) combined with the recent de-
scriptions of repressive functions of re-
lated ETS factors leads us to hypothesize
that ETS factors may silence critical genes
for proper erythroid development.
In summary, we provide a compre-
hensive whole-genome map of DNA
methylation that can be easily integrated
with other occupancy data. The sequences
subject to differential methylation during
myeloid development lead us to suggest
that DNA methylation may offer an addi-
tional layer of modulation of key hema-
topoietic transcription factors. This study
provides insight into the interplay be-
tween DNA methylation and transcrip-
tional networks that are involved in he-
Enrichment of primary mouse cells
Hematopoietic stem cells and common myeloid progenitor cells
were harvested from adult female C57BL/6 bone marrow. After
lysis of red cells in ACK lysing buffer (BioWhittaker), ;109cells
were subjected to lineage depletion using the following rat anti-
mouse antibodies: CD8a, CD4, CD11b, Ly-6G/Ly-6C, CD45R, and
Ter119 (BD Biosciences). Lineage depletion was performed as pre-
viously described (Nemeth et al. 2003). Lineage-negative cells
(lin?) were stained with PE anti-mouse Sca1(clone D7) and APC
anti-mouse CD117 (clone 2B8; BD biosciences). Lin?Sca-1+c-kit+
(HSC; 1%–2% of lineage depleted cells) and lin?Sca-1?c-kit+
instrument. Images from a representative sort are shown in Sup-
plemental Figure S1. Cells from five sorts (HSC) and two sorts
(CMP) were combined to generate sufficient cells (;1 3 106to
2 3 106) for analysis. Erythroblasts were obtained from C57BL/6 d
13.5 embryonic fetal livers disrupted into a single-cell suspension
with a 21-gauge needle and stained with APC anti-mouse Ter119
and FITC anti-mouse CD71 antibodies (BD Biosciences). The cells
were sorted into the five populations described by Zhang et al.
(2003). Cytospins were stained with May-Grunwald Giemsa to
demonstrate that the R3 population (CD71+Ter119+) contained
late basophilic erythroblasts (Supplemental Fig. S1).
MBD2 enrichment of methylated DNA
Genomic DNA was isolated from enriched cells with the QIAGEN
Puregene kit and sonicated to 200- to 400-bp fragments. MBD2
view of the Eng locus on chromosome 2. Transcription factor consensus sites (TRANSFAC IDs) are in-
dicated above the MBD-seq data in regions of significant peaks. QPCR data verifying enriched ChIP
binding of FLI1 (B) and ELF1 (C) at three sites of methylation peaks throughout Eng. Site 1, an ERY-
specific peak, is within the proximal promoter; site 2, an ERY-specific intronic peak; and site 3, a pro-
statistically significant differences of P = 0.004 (site 1, FLI1), P = 0.009 (site 1, ELF1), P = 0.021 (site 2,
ELF1), and P = 0.012 (site 3, FLI1).
FLI1 and ELF1 occupancy of methylation peaks in the Eng gene. (A) UCSC Genome Browser
Genome-wide DNA methylation in hematopoiesis
enrichment was performed with the Active Motif MethylCollector
kit. Approximately 1 mg of sonicated genomic DNA was incubated
with MBD2-His-conjugated protein and magnetic beads according
to the manufacturer’s protocol. Between four and eight MBD2-
genomic DNA reactions for each biological replicate were purified
simultaneously and pooled post-enrichment. After enrichment,
both the methylated fraction and supernatant fractions were pu-
rified with QIAGEN DNA purification columns. Quantitative PCR
amplification of the differentially methylated regions regulating
the imprinting of Snrpn and Rasgrf1 and the unmethylated CpG
island promoter of Actb was performed with SYBR Green PCR
master mix (Applied Biosystems), and was used to validate the
enrichment of methylated DNA using the MBD2-pull-down ap-
proach (Supplemental Fig. S3).
Bisulfite sequencing validation
Genomic DNA from HSCs, CMPs, and ERYs was bisulfite-converted
with the EZ DNA Methylation-Direct kit (Zymo Research). Briefly,
500 ng of DNA was converted according to a standard protocol.
The converted DNA was PCR-amplified with bisulfite primers
designed using MethPrimer (Li and Dahiya 2002). The primer se-
quences are listed in Supplemental Table S5. PCR-amplified bi-
sulfite products were cloned using the TOPO TA Cloning kit
(Invitrogen) and sequenced. Bisulfite sequences were analyzed
with the Quantification Tool for Methylation Analysis (Kumaki
et al. 2008).
Next-generation sequencing of MBD2-enriched genomic DNA
Two biological replicates of each enriched cell population and one
supernatant sample per cell type were submitted for high-
throughput sequencing analysis. Between 225 and 540 ng of
MBD2-enriched DNA and 1 mg of supernatant for each cell type
were used to construct DNA libraries according to the Illumina
protocol. The libraries were sequenced on the Illumina Genome
Analyzer platform, and 36-bp single-end reads were used to
Mapping and peak calling for MBD2 enrichment
Sequenced reads were mapped to the mouse genome (UCSC as-
sembly mm9, NCBI build 37) using the ELAND (AJ Cox, unpubl.)
short-read alignment program. Peaks for each cell type were called
using MACS (Zhang et al. 2008) with a P-value threshold of P <
10?5. Sequenced reads from the matched supernatant were used as
a control for each cell type. When MACS was unable to build a
model for a given treatment/control pair, the model restrictions
were lowered to compensate. Peak calls made on replicates were
post-processed to generate a confident set. Replicate peaks that
overlapped by >200 bp were considered for further analysis; at
this cutoff the majority of overlaps were retained (Supplemental
The final sets of peaks were partitioned according to the ge-
nomic segments they occupy based on the RefSeq gene coordinate
map available for the mm9 genome build. Since DNA methylation
peak lengths average 800 bp (Supplemental Table S2), peaks often
span intron and exon segment boundaries. To assess the distribu-
tion of DNA methylation within the context of more discrete se-
quences within genes, the mean value of a peak range was used to
assign it to a partition.
In silico gene expression analysis
Gene expression was determined using the BloodExpress database
(Miranda-Saavedra et al. 2009). Briefly, data sets representing cells
obtained from similar purification strategies were selected and
compiled for each cell type. HSC gene expression represented the
union of the LT-HSC, ST-HSC, and MPP data sets from multiple
gene expression studies (Akashi et al. 2003; Chambers et al. 2007;
Mansson et al. 2007; Ficara et al. 2008). CMP gene expression
represents the compilation of similarly purified c-kit+, sca1?pro-
genitor expressed genes (Akashi et al. 2003; Jankovic et al. 2007)
and ERY gene expression was determined based from Ter119+
normoblasts (Chambers et al. 2007). Full details of the cells used in
the BloodExpress databaseare availablefrom http://hscl.cimr.cam.
The complete set of putative binding sites of length 5–10 were
enumerated using the WordSeeker approach (Lichtenberg et al.
2010). Each site was evaluated for its overrepresentation in regard
to its sequence coverage using Markov chain background models
(Lichtenberg et al. 2009) of varying order, ranging from 0 to the
order = site length ? 2).
The set of enumerated and scored binding sites was sorted in
according to a word factor–based maximization [a site y is dis-
carded if it is completely contained in a site x of equal or longer
length and larger overrepresentation: x > y if x = uyv and score(x) >
score(y), with u and v being non-empty factors themselves]. The
top 25 putative binding sites were retained for further analysis.
The setof predicted binding sites was comparedwith the setof
known transcription factor binding sites annotated in TRANSFAC
sites were corrected for overlap to ensure that the TRANSFAC sites
colocalized to the predicted sites in the input sequences.
For each known and putatively involved transcription factor, the
number of input data sets in which it occurs was computed. Using
the matrix2png application (Pavlidis and Noble 2003), a heatmap
was created correlating each of the transcription factors with the
input data sets characterizing the different stages of differentia-
data sets that share the transcription factor involvement to allow
highlighting of unique combinations.
Occupation-methylation correlation analysis
ChIP-seq localization data obtained by Wilson et al. (2010) were
overlapped with the methylation peaks. Random peaks of equal
cardinality and size were generated and used to quantify the
overlap expected by chance. Based on 1000 bootstrapping itera-
tions, the tabulated expected average overlap and standard de-
viation were computed. In congruence with the observed overlap,
Z-scores were inferred and subsequently used to compute P-values
using the R toolkit (Ihaka and Gentleman 1996).
Primary mouse CMP and ERY cells were sorted as described above
and fixed with 1% formaldehyde for 10 min at room temperature.
Fixation was quenched with 0.125 M glycine for 10 min at room
temperature. Cells were washed twice in 13 PBS containing pro-
tease inhibitor and frozen at ?80°C. Chromatin immunoprecipi-
tation was performed using the Magna ChIP A/G kit (Millipore).
Briefly, cells were lysed and sonicated to 200- to 400-bp fragments;
Hogart et al.
1416 Genome Research
1 3 106cells were used for each IP. Antibodies for FLI1 (rabbit
polyclonal,Abcam) andELF1(C-20) (rabbitpolyclonal;SantaCruz
Biotechnology) were used for immunoprecipitation according to
control, and enrichment was determined by quantitative PCR as
described above.Alist of allof theChIP primersused is availablein
Supplemental Table 6. All reactions were performed in duplicate,
and IgG pull-down was used for normalization with the DCT
method. Significant differences in occupancy between cell types
was determined by a Student’s t-test.
The data have been submitted to the NCBI Gene Expression
Omnibus (GEO) (http://www.ncbi.nlm.nih.gov/geo/) under ac-
cession no. GSE38354 and are also available on our website at
This work was funded from NHGRI intramural funds. A.H. is
funded by the National Institute of General Medical Sciences
Pharmacology Research Associate Training Program. We thank
thank the NHGRI Embryonic Stem Cell and Transgenic Mouse
Core Facility for animal resources.
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1418 Genome Research