Copy Number Variant Analysis of Human Embryonic Stem Cells
HAO WU,a,bKEVIN J. KIM,a,bKSHAMA MEHTA,cSALVATORE PAXIA,dANDREW SUNDSTROM,d
THOMAS ANANTHARAMAN,dALI I. KURAISHY,eTRI DOAN,cJAYATI GHOSH,cAPRIL D. PYLE,f,g,h,i
AMANDER CLARK,g,h,i,jWILLIAM LOWRY,g,h,i,jGUOPING FAN,g,h,i,kTIM BAXTER,cBUD MISHRA,dYI SUN,a,b,g,h,i
MICHAEL A. TEITELLe,g,h,i
Departments ofaPsychiatry and Biobehavioral Sciences,bMolecular and Medical Pharmacology,ePathology and
Laboratory Medicine,fMolecular Immunology and Medical Genetics,jMolecular, Cell and Developmental Biology,
andkHuman Genetics, David Geffen School of Medicine,gMolecular Biology Institute,hJonsson Comprehensive
Cancer Center, andiBroad Center of Regenerative Medicine and Stem Cell Research, University of California, Los
Angeles, Los Angeles, California, USA;cAgilent Laboratories, Santa Clara, California, USA;dNew York
University/Courant Bioinformatics Group, Courant Institute of Mathematical Sciences, New York University, New
York, New York, USA
Key Words. Embryonic stem cells • Oligonucleotide array sequence analysis • Genome stability • Multipoint statistics •
Differences between individual DNA sequences provide the
basis for human genetic variability. Forms of genetic varia-
tion include single-nucleotide polymorphisms, insertions/du-
plications, deletions, and inversions/translocations. The ge-
nome of human embryonic stem cells (hESCs) has been
characterized mainly by karyotyping and comparative
genomic hybridization (CGH), techniques whose relatively
low resolution at 2–10 megabases (Mb) cannot accurately
determine most copy number variability, which is estimated
to involve 10%–20% of the genome. In this brief technical
study, we examined HSF1 and HSF6 hESCs using array-
comparative genomic hybridization (aCGH) to determine
copy number variants (CNVs) as a higher-resolution method
for characterizing hESCs. Our approach used five samples
for each hESC line and showed four consistent CNVs for
HSF1 and five consistent CNVs for HSF6. These consistent
CNVs included amplifications and deletions that ranged in
size from 20 kilobases to 1.48 megabases, involved seven
different chromosomes, were both shared and unique be-
tween hESCs, and were maintained during neuronal stem/
progenitor cell differentiation or drug selection. Thirty
HSF1 and 40 HSF6 less consistently scored but still highly
significant candidate CNVs were also identified. Overall,
aCGH provides a promising approach for uniquely identi-
fying hESCs and their derivatives and highlights a potential
genomic source for distinct differentiation and functional
potentials that lower-resolution karyotype and CGH tech-
niques could miss. STEM CELLS 2008;26:1484–1489
Disclosure of potential conflicts of interest is found at the end of this article.
Human embryonic stem cells (hESCs) that have been cultured
for extended periods may retain a diploid karyotype [1–3] or
may demonstrate chromosomal instability, often marked by
translocations and aneuploidy. This chromosome-scale instabil-
ity probably reflects a selective advantage during growth over
time in suboptimal conditions [1, 4, 5]. Current approaches used
to evaluate hESC genome integrity include mainly G-banding
metaphase karyotyping and metaphase-based comparative
genomic hybridization (CGH). These techniques deliver a sen-
sitivity estimated at 5–10 megabases (Mb) for karyotype down
to 2–3 Mb for CGH [6, 7]. A recent study also evaluated
single-nucleotide polymorphisms (SNPs) for early- and late-
passage hESCs and determined that an SNP fingerprint could
uniquely identify samples . However, copy number variants
(CNVs), representing amplified or deleted regions ranging in
size from 1 kilobase (kb) up to 1.0 Mb or more [9, 10], have
been recently recognized as a major source of human genome
variability that potentially exceeds SNP differences between
individuals by more than threefold and is below the detection
threshold of most current techniques [11–14]. Using array-
comparative genomic hybridization (aCGH), a well-established
microarray-based nucleic acid hybridization method with kb-
scale resolution [15–18], studies of somatic cells from pheno-
typically normal individuals show, on average, ?11 CNV dif-
ferences between unrelated genomes [12, 14]. CNV differences
among individuals may at least partially explain human unique-
ness, whereas CNV similarities among individuals may indicate
subpopulation relatedness. This is because particular CNVs
have been shown to affect gene expression, influence pheno-
typic variation and adaptation by disrupting genes and altering
dosage compensation, cause a variety of diseases, and confer
risk to complex traits, such as HIV-1 susceptibility and glomer-
ulonephritis [19–29]. Positive environmental selection has been
postulated to impact CNV genes, such as amplification of the
salivary amylase gene from populations with high-starch diets
Correspondence: Michael A. Teitell, M.D., Ph.D., Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at
UCLA, 675 Charles Young Drive South, 4-762 MRL, Los Angeles, California 90095-1732, USA. Telephone: 310-206-6754; Fax:
310-267-0382; e-mail: email@example.com Received November 26, 2007; accepted for publication March 18, 2008; first published online
in STEM CELLS EXPRESS March 27, 2008. ©AlphaMed Press 1066-5099/2008/$30.00/0 doi: 10.1634/stemcells.2007-0993
EMBRYONIC STEM CELLS
. These observations on the extent and influence of CNVs in
the genomes of somatic cells leave open questions regarding the
extent to which CNVs account for hESC genomic variability
and whether individual hESCs have characteristic gains or
losses of genetic material that may influence their replication/
proliferation, differentiation, or functional potentials. It is also
unclear whether genomic regions below karyotype or metaphase
CGH detection limits are stable over culture time or with dif-
fering culture conditions, such as positive drug selection. There-
fore, in this brief technical assessment, we used a high-density
aCGH platform to determine the extent to which two hESC lines
with distinct neuronal differentiation potentials, HSF1 and
HSF6, display CNVs.
MATERIALS AND METHODS
NIH-registered hESCs HSF1 (46XY; UC-0001) and HSF6 (46XX;
UC-0006) were cultured on irradiated CF1 mouse embryonic fibro-
blasts (MEFs) in Dulbecco’s modified Eagle’s medium-high glu-
cose supplemented with 20% knockout serum replacer (Invitrogen,
Carlsbad, CA, http://www.invitrogen.com), basic fibroblast growth
factor (4–10 ng/ml), 1 mM glutamine, 1% nonessential amino acids
(with or without 1% penicillin/streptomycin), 0.1 mM 2-mercapto-
ethanol with daily medium changes. hESCs were passaged every
4–6 days by incubation with 1 mg/ml collagenase IV ? dispase
(Invitrogen) for 10–20 minutes at 37°C. Conditions for the differ-
entiation and maintenance of neuronal stem/progenitor cells (NPCs)
from HSF1 and HSF6 have been described . Drug-resistant
HSF1 lines were generated by culturing with 250 ?g/ml G418 or
100 ?g/ml hygromycin for 14 days on DR4 MEFs following trans-
duction with neomycin- or hygromycin-resistant lentiviruses, re-
spectively. Medium was changed every 2 days, and after 14 days,
drug-selected hESCs were passaged onto CF1 MEFs.
Genomic DNA (gDNA) was prepared and quantified from HSF1
and HSF6 cells by standard techniques. Sample (0.5–1.0 ?g) and
sex-mismatched normal reference gDNA (Promega, Madison, WI,
http://www.promega.com) was digested with AluI and RsaI and
labeled with either Cy3- or Cy5-dUTP (Agilent Genomic Labeling
Kit Plus; Agilent Technologies, Santa Clara, CA, http://www.
agilent.com). Labeled gDNA products were purified using Micro-
con YM-30 filtration devices (Millipore, Bedford, MA, http://www.
millipore.com) and volume-adjusted, and DNA yield and level of
dye incorporation were measured using an ND-1000 spectropho-
tometer (NanoDrop, Rockland, DE, http://www.nanodrop.com).
Specific Cy5- and Cy3-labeled DNA sample pairs were combined
and mixed with human Cot-1 DNA (Invitrogen), 10 ? blocking
agent, and 2 ? hybridization buffer (Agilent Technologies). Sam-
ples were heated at 95°C for 3 minutes, incubated for 30 minutes at
37°C, and then hybridized to human genome microarrays using
Agilent SureHyb chambers. aCGH was performed on high-density
oligonucleotide microarrays containing ?236,000 (244K) coding
and noncoding 60-mer oligonucleotide sequences (G4411B; Agilent
Technologies). This 244K microarray was generated from human
genome assembly build 35 (March 2004; UCSC hg17) and has a
6.4-kb average probe spatial resolution that is biased for known
genes, microRNAs, gene promoters, intergenic regions, and telo-
meres. The 244K microarray is biased against regions of the ge-
nome that contain segmental duplications and repetitive elements,
which is where CNVs are often located, and has 63,900 of 236,000
array probes overlapping with known CNVs, for approximately
27% known CNV coverage. The hybridization chambers were
placed in a 65°C rotisserie oven and rotated at 20 rpm for 40 hours,
followed by washing according to the procedures described in
Agilent Oligonucleotide Array-Based CGH for Genomic DNA
Analysis protocol version 4. Microarray slides were scanned imme-
diately using an Agilent microarray scanner. Data were extracted
using Feature Extraction software, version 18.104.22.168 (Agilent Tech-
nologies, Santa Clara, CA, http://www.agilent.com).
aCGH data sets were analyzed with two independently developed
software packages, BuddhaCGH Pipeline and CGHAnalytics 3.4
(Agilent Technologies). BuddhaCGH Pipeline was developed to
analyze genomic array data in a technology-agnostic manner (S.
Paxia et al., manuscript in preparation) and has been used to
evaluate CNVs in cancer and to identify oncogenes and tumor-
suppressor genes from genomic data, either alone or in conjunction
with transcriptome data [32, 33]. CGHAnalytics 3.4, a software
platform developed by Agilent Technologies, provided an indepen-
dent statistical approach for determining genomic amplified and
deleted regions. These two statistical tools differed in subtle ways in
how they normalized the data, removed noise, partitioned the data
into segments of equal copy number values, and interpreted seg-
ments. Nevertheless, they were expected to concur on the statisti-
cally most significant conclusions, to thereby increase confidence in
the results of the joint analyses.
In CGHAnalytics 3.4, a data normalization step enables the
identification of probes that behave similarly with respect to both
the test and control samples (i.e., logarithms of their intensity ratios
are 0). Consequently, normalization of the log ratios also provides
a basis for identifying and characterizing those probes that signifi-
cantly deviate in copy number. Under the assumption that almost all
pairs of consecutive probes sample regions of similar copy number,
the log ratios of most pairs of consecutive probes are expected to be
equal, and significant deviations from near-equality (estimated with
respect to the expected probe-to-probe noise) were used to identify
genomic aberrations. The deviation is measured as the SD of the
derivative of the log ratio for an array and is used in estimating the
statistical significance of observed aberrations. All regions of sta-
tistically significant copy number changes are identified using the
aberration detection module-1 (ADM-1) algorithm . Stable re-
gions of amplification or deletion across multiple samples of each
hESC type were called visually, with a penetrance of 100% reported
in Tables 1 and 2.
Table 1. HSF1 CNV intervals identified by both BuddhaCGH Pipeline and CGHAnalytics 3.4 platforms
start Interval endSizeGenes
Amp20 q11.2129.309999 30.7800011.48 Mb
DEFB115–119, DEFB121, DEFB123, DEFB124,
REM1, HM13, ID1, COX4I2, BCL2L1, TPX2,
MYLK2, FKHL18, DUSP15, TTLL9, PDRG1,
XKR7, C20orf160, HCK, TM9SF4, TSPYL3,
PLAGL2, POFUT1, KIF3B, ASXL1, C20orf112,
Abbreviations: Amp, amplified; Chr, chromosome; CNV, copy number variant; Del, deleted; ID, identification; kb, kilobases; Mb, megabases.
Wu, Kim, Mehta et al.
BuddhaCGH uses a Bayesian maximum a posteriori (MAP)
algorithm to find segments of genomic amplifications and deletions,
under a set of noninformative priors regarding the distributions of
segmental breakpoints and segment lengths with penalty terms
determined by the intersegment t statistics. The optimization prob-
lem admits an efficient implementation under a dynamic program-
ming formulation and leads to a robust estimator by accounting for
outlier probe values. The data sets were normalized prior to seg-
mentation so that different hESC data sets could be directly com-
pared. Since in both analyses each segment was constrained to be no
smaller than three contiguous probes, the algorithms can catch a
segmental change at ?10–15-kb resolution.
The BuddhaCGH pipeline introduced a multilocus scoring
function to identify genomic intervals that show a stable or possibly
time-dependent signature, to detect the possible evolution of ampli-
fications or deletions over culture time. For example, a score func-
tion “rewarded” an amplified interval that emerged at an early
period in time but stabilized over time. The same score function also
“penalized” these values when measurements or biological noise
corrupted the signals. The results of this analysis for HSF1 and
HSF6 amplifications and deletions were tabulated, with the entries
sorted by score and filtered to include only score values above a
threshold. By visually comparing the spatial distributions of the
high-scoring intervals and by aiming to select no more than one or
two regions per chromosomal arm, we determined that a threshold
of 0.2 or above was reasonable. For a conservative interplatform
comparison, we used a more stringent threshold of 0.7 to lower the
number of false-positive intervals and genes.
We compared the results from BuddhaCGH and CGHAnalytics
3.4 to identify regions of concordance. Supplemental online Table 1
includes all of the data from the two different software systems,
including regions where only one or the other software platform
identified an amplified or deleted region above the cutoff threshold.
Quantitative Real-Time Polymerase Chain Reaction
Quantitative real-time polymerase chain reaction (qPCR) was per-
formed with an iCycler using iQ SYBR Green Supermix (Bio-Rad,
Hercules, CA, http://www.bio-rad.com) and male and female refer-
ence, HSF1, and HSF6 gDNA samples. Specificity for each primer
pair was examined by melting curve functionality and agarose gel
electrophoresis. To calculate gene copy number differences between
reference normal gDNA (Promega) and HSF1 or HSF6 gDNA, the
threshold cycle of each sample was normalized to a negative control
gene, SRC, which did not show copy number differences between
reference and HSF1 or HSF6 gDNAs in 10 independent aCGH
experiments. Fold change between reference gDNA and HSF1 or
HSF6 gDNA was calculated based on the 2???Ctmethod. Primer
sequences used for qPCR are listed in supplemental online Table 2.
Error bars represent the SEM.
HSF1 and HSF6 hESCs were recently shown to have normal
diploid karyotypes at passage 25 , with HSF1 further char-
acterized as 46XY to at least passage 29 (University of Califor-
nia, San Francisco, NIH Registry Stem Cells, http://www.
escells.ucsf.edu) and HSF6 further determined as 46XX to
passage 120 , indicating chromosome level genomic stabil-
ity. To determine subkaryotypic genome heterogeneity, aCGH
using ?236,000 feature, 60-mer oligonucleotide probe microar-
rays was used. The choice of this platform versus an SNP array
was not straightforward, as each approach offers advantages and
disadvantages. For example, SNP arrays can provide both copy
number estimations and genotype information in cases of copy-
neutral aberrations, such as uniparental disomy [36, 37]. In a
recent comparison, Agilent 60-mer oligonucleotide microarrays
provided the highest sensitivity and specificity of CNV detec-
tion, whereas the newer SNP arrays (e.g., Affymetrix SNP 6.0
[Affymetrix, Santa Clara, CA, http://www.affymetrix.com] and
Illumina Linkage IV [Illumina Inc., San Diego, http://www.
illumina.com]) require polymerase chain reaction-probe com-
plexity reduction, and their performance has yet to be deter-
mined, precipitating our platform choice [38, 39].
HSF1 gDNA was assessed from two pluripotent controls
grown in different laboratories with no in vitro manipulations,
from stably selected G418 or hygromycin-resistant subclones
following retroviral integration of resistance genes, and from
NPCs differentiated from HSF1 hESCs at passage 2, providing
five independent assessments under a variety of growth condi-
tions. HSF6 cells were differentiated to NPCs as recently de-
scribed , and gDNA was evaluated at passages 1, 2, 3, 4, and
9, also providing five independent assessments over a 2-month
period of continuous culturing after hESCs were converted/
differentiated into NPCs. An important aspect of this study was
the distinct culturing conditions and passage numbers used for
aCGH analysis, because a main study goal was to determine
CNV region stability in a variety of culturing contexts, as occurs
in laboratories worldwide.
Resulting aCGH data were analyzed with two independently
developed software packages. CGHAnalytics 3.4 (http://www.
chem.agilent.com/Scripts/PDS.asp) uses the ADM-1 algorithm
, with a stringent scoring threshold of 8. BuddhaCGH Pipeline
is a custom data analysis package that includes a substrate-specific
data normalization module, a MAP segmenter module  to
partition the normalized copy-number data, and a multipoint sta-
tistical analysis module  that scores genomic intervals for how
well they support a particular biological hypothesis (supplemental
online text). With each analysis package, a CNV interval required
a minimum of three consecutive concordant probes to score posi-
tive for amplification or deletion. Variant segment chromosome
mapping and identification of genes contained within variant seg-
ments used human genome assembly build 35 (hg17). CNV tags
were obtained from the most recent (October 24, 2007) The Centre
for Applied Genomics (TCAG) Database of Genomic Variants
using build 35, which currently contains 11,784 CNVs (http://
Table 1 shows consistently amplified and deleted regions in
HSF1 over five biological and technical replicates, performed
once for each growth condition, as determined by both
CGHAnalytics 3.4 and BuddhaCGH Pipeline. Four candidate
genomic intervals, one amplification region and three deletion
Table 2. HSF6 CNV intervals identified by both BuddhaCGH Pipeline and CGHAnalytics 3.4 platforms
Amp/Del Chr LocusInterval startInterval end SizeGenesCNV locus Variation ID
Abbreviations: Amp, amplified; Chr, chromosome; CNV, copy number variant; Del, deleted; ID, identification; kb, kilobases.
Embryonic Stem Cell CNVs
regions, provide stable CNVs that could represent the genetic
makeup of the inner cell mass from which this line was derived
or that may be part of an early adaptation to derivation and
subsequent culturing in conditions that did not select against
these CNVs. This number of consistent CNVs is a conservative
underestimate of the likely number of CNVs because both
programs had to positively score at least a three-probe interval,
and each program was set with high stringencies for detection.
Thirty additional candidate HSF1 CNV intervals, at slightly
lower (and therefore detected in three or four aCGH runs instead
of all five) but still highly significant threshold scores, are
shown in supplemental online Table 1.
A 1.48-Mb stable amplified region involving 30 genes was
detected at 20q11.21 (supplemental online Figs. 1, 2), whereas
three stable deleted regions averaging 40–50-kb each and con-
taining at least part of a single coding gene were detected at
6p21.32, 7q34, and 22q11.23. Among the affected genes are
copy number variants in the BCL2L1 gene, which regulates cell
survival and death ; ID1, which encodes a protein that binds
helix-loop-helix transcription factors to inhibit lineage commit-
ment and affect cell growth, senescence, and differentiation; and
HLA-DRB5, which is part of the locus that encodes histocom-
patibility antigens (Table 1). The 1.48-Mb amplification at
20q11.21 is a new CNV locus providing a novel CNV variation
ID not previously reported in the TCAG Database of Genomic
Variants, whereas the 40-kb deletion at 6p21.32 provides a
novel CNV variation ID within the reported 1,673 CNV locus.
qPCR was used to evaluate five genes within the four
consistently identified HSF1 CNV regions, including two genes
from amplified regions and three genes from deleted regions
(Fig. 1). In each case, the aCGH result was confirmed. Interest-
ingly, CNV-associated genes at 7q34 and 22q11.23 showed
homozygous deletions, whereas HLA-DRB5 at 6p21.32 was
haploinsufficient and two genes at 20q11.21 showed low-level
copy number amplification.
Supporting a 1.48-Mb amplification at 20q11.21, 11 genes
within this CNV region, including a cluster of 6 linearly arranged
genes (HM13, ID1, COX412, BCL2L1, TPX2, and MYLK2) and a
smaller cluster of 3 linearly arranged genes (KIF3B, ASXL1, and
C20orf112), are all overexpressed by ?1.5–2.5-fold in HSF1
NPCs versus HSF6 NPCs , which lacks this unique CNV
amplification (Table 2). Tissue typing also shows that HLA-DRB5
is not an expressed allele of the HLA locus in HSF1 hESCs,
providing an example of a biallelic gene that is deleted in one allele
Fan, data not shown). HSF1 hESCs grown under selection or
Figure 1. Quantitative real-time polymerase chain reaction validation of consistent and variably detected CNV region genes. Abbreviations: aCGH,
array-comparative genomic hybridization; amp, amplified; Chr, chromosome; CNV, copy number variant; Ctrl, control; del, deleted.
Wu, Kim, Mehta et al.
induced to NPCs at passage 2 demonstrated the same four CNVs,
indicating stability for these previously altered genomic regions
under a variety of culturing conditions.
Table 2 shows the stable CNV regions for HSF6 hESCs detected
by both analysis programs over five biological and technical rep-
licate samples and includes one amplified region and four deleted
regions. A 20-kb amplified region was detected at 1q21.3, whereas
a 70-kb deleted region was seen at 19p12, and 40-kb deleted
regions were identified at 4q13.2, 6p21.32, and 22q11.23. Dele-
tions at 6p21.32 and 22q11.23 were shared with HSF1 hESCs and
include a copy number change in the biallelically expressed HLA-
DRB5 histocompatibility antigen locus, which is also not expressed
in HSF6 hESCs (Reed and Fan, data not shown). Two CNV
regions, 4q13.2 and 19p12, lack any known coding genes, whereas
CNV regions at 1q21.3 and 22q11.23 affect single genes whose
expression is unaltered in HSF1 NPCs versus HSF6 NPCs with
gene expression microarray analysis . Forty additional candi-
date HSF6 CNV intervals, at slightly lower (and therefore detected
in three or four instead of all five aCGH runs) but still highly
significant threshold scores are shown in supplemental online Ta-
ble 1. Because of the serial-passage component of HSF6 hESC
analysis, 18 regions that were altered in only one or two early
passages but not later passages were considered technical or scor-
ing artifacts. One small amplified region on 11p15.5 appeared
during passages 4 and 9 (supplemental online Table 1), suggesting
a potential subkaryotpic region of instability with extended culture
qPCR was used to evaluate five consistently identified HSF6
CNV regions (Table 2), including one amplified CNV gene and
four loci with two identified genes from four CNV deleted regions
(Fig. 1). In each case, the aCGH result was again confirmed.
Interestingly, homozygous deletions were identified at 4q13.2,
19p12, and 22q11.23 (glutathione S-transferase 1 [GSTT1]),
whereas HLA-DRB5 at 6p21.32 was haploinsufficient and LCE3C
at 1q21.3 showed low-level copy number amplification. Shared
CNVs containing HLA-DRB5 and GSTT1 showed identical copy
number aberrations between HSF1 and HSF6 cells for unknown
reasons. Two additional genes from lower threshold scoring CNV
regions (supplemental online Table 1) were also evaluated by
and NOTCH1 from HSF1 not confirming the lower scoring thresh-
old aCGH analysis. These results reveal the detection robustness
associated with stringent scoring from two independent data anal-
ysis packages and the likelihood that multiple lower threshold
scoring candidates also identify CNV regions.
The International Stem Cell Initiative has undertaken the initial
characterization of 75 hESC lines, which includes DNA finger-
printing of 10 short tandem repeat loci for each line to establish its
unique identity . Thus far, the genomes of most hESCs have
been characterized by relatively low-resolution, 2–10-Mb genome-
wide techniques. Here, we evaluated the utility of identifying
CNVs in hESCs using kb-resolution aCGH. Although SNP anal-
ysis provides nucleotide resolution, the sequence variation in ab-
solute nucleotide numbers between two independent human ge-
nomes, including by extension two different hESC genomes, is
estimated to be 5–10-fold higher because of amplified or deleted
CNV regions compared to SNP variations alone . Therefore,
CNV differences could contribute as much or more genetic vari-
ability than SNP differences to controlling hESC differentiation
Two independent analytic programs using five replicate sam-
ples with stringent scoring criteria showed that HSF1 and HSF6
have both shared and unique amplified and deleted genomic re-
gions. Two of the four stringently identified CNVs in HSF1 and
five stringently identified CNVs in HSF6 were shared between
these hESCs. Shared homozygous loss of GSTT1 (Fig. 1), which
catalyzes the conjugation of reduced glutathione to various elec-
trophilic and hydrophobic compounds and has been implicated in
carcinogenesis, could influence the selection of specific hESCs for
study or therapy. Additional CNV differences between these
hESCs are likely to emerge from the 30 candidate HSF1 CNVs and
40 candidate HSF6 CNVs that scored positively in three or four of
the five replicate samples for each hESC (supplemental online
Table 1; Fig. 1), such as a confirmed homozygous deletion in the
GALNT17 gene in HSF6, thereby increasing genome uniqueness
for these lines. In fact, the number of CNVs that ultimately distin-
guish HSF1 and HSF6 hESCs, and by extension that are likely to
distinguish all hESCs from one another, are likely to be similar to
the estimated average of 11 CNV differences between individuals
reported for somatic cells [12, 14].
HSF1 and HSF6 hESCs were chosen for this study because
they were derived under similar protocols from a single institution
and yet they exhibit unique neuronal differentiation potentials un-
der identical culturing conditions . Although the HSF6 line
tends to produce midbrain GABAergic (PAX2- and GAD67-pos-
identities (e.g., dopaminergic, serotonergic, and cholinergic neu-
rons from midbrain, hindbrain, and spinal cord), the HSF1 line
tends to generate forebrain-like glutamatergic and GABAergic
neurons. It is not yet known what genetic or epigenetic factors
influence these distinct neuronal fate decisions. However, CNV
differences could participate in these differential outcomes. Al-
though it is tempting to consider a direct copy number-gene ex-
pression relationship for controlling distinct differentiation fates,
and approximately twofold increased expression of BCL2L1 is
retained in 20q11.21 amplified HSF1 hESCs and NPCs compared
with HSF6 hESCs and NPCs (data not shown), this is almost
certainly an oversimplification. For example, there are numerous
reports of wide variation in gene and protein expression associated
with genes within CNV regions. Because gene expression depends
on lineage, state of differentiation within a lineage, and a variety of
genetic (copy number, point mutation, and rearrangement) and
epigenetic (DNA methylation, histone modification, and post-tran-
scriptional stability) factors, a strictly linear correlation between
gene expression level and CNV status is unlikely. This is also true
for cells in two different differentiation states, such as hESCs and
NPCs. If such a linear relationship did occur, it would tend to
negate the impact for all of these affiliated factors beyond simple
increased or decreased gene copy number. Clearly, additional stud-
present in distinct CNV regions between HSF1 and HSF6 hESCs
control differentiation potential, such as the impact of specific
gain-of-function and loss-of-function alterations followed by NPC
CNVs detected from somatic cells and tissues, like SNPs detected
from similar sources, could represent variations of normality, or
so-called “benign CNVs, ” as opposed to “pathogenic CNVs” .
A benign CNV or SNP is the likely interpretation when a genomic
imbalance is detected in an individual and that person’s healthy
parent(s). However, for most if not all hESCs, tests on the parent(s)
of origin are not available, and the CNV in question may or may
not affect not only the differentiation potential and function of a
Embryonic Stem Cell CNVs
particular hESC but also any derivative therapeutic cells or tissues. Download full-text
The observation that 16 of 34 (47%) of the genes listed in the
consistent CNV intervals of Tables 1 and 2 are represented in the
Online Mendelian Inheritance in Man (http://www.ncbi.nlm.nih.
gov/omim) database, without even considering any noncoding
RNAs within these CNV intervals, suggests that many copy num-
ber variant regions within HSF1 or HSF6 could have significant
disease relevance as well.
This study was supported by California Institute for Regenera-
tive Medicine (CIRM) Predoctoral Training Grant T1-00005
(H.W.) and CIRM Seed Grant RS1-00313 (to M.A.T.). Work
from the New York University/Courant Bioinformatics group
was supported by two National Science Foundation (NSF) ITR
grants and an NSF-EMT grant (to B.M.). M.A.T. is a Scholar of
the Leukemia and Lymphoma Society (White Plains, NY).
H.W. and K.J.K. contributed equally to this work.
DISCLOSURE OF POTENTIAL CONFLICTS
K.M., T.D., J.G., and T.B. are employees of Agilent Technol-
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Wu, Kim, Mehta et al.