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Supplementary data
Spatio-temporal heterogeneity characterize the genetic landscape of
pheochromocytoma and defines early events in tumorigenesis.
Crona et al.
Patients and samples........................................................................................................... 3Tissue collection............................................................................................................................ 3Sample preparation and nucleic acid extraction...................................................................3
Sample Sequencing............................................................................................................. 4Targeted Deep Sequencing......................................................................................................... 4PCR amplification. fragment separation and Sanger Sequencing....................................5High throughput sequencing of selected PCR amplicons....................................................5
SNP array genotyping and raw data analysis...............................................................7
Pipeline for resolving absolute ploidy and purity in Pheochromocytoma...............7Determination of LogR intensities and B allele frequencies................................................7Copy number classification........................................................................................................ 8Determination of clonal proportions........................................................................................9Inferring allele specific copy number status by establishing relationships between logR and absolute ploidy............................................................................................................. 9
Results................................................................................................................................. 11SNP array Genotyping..............................................................................................................15Results and validation of absolute ploidy and clonal fractions........................................15Estimation of sample tumour cellularity...............................................................................17Comparison of robustness of the determination of variant frequencies........................19
References.......................................................................................................................... 23
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Supplementary Figure 1
Overview of the workflow executed in the current study.
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Patients and samples
Tissue collectionAll tumours samples were obtained from surgical specimens that had been collected
between 1988-2013 at the Unit of Endocrine Surgery, Uppsala Academic Hospital,
Uppsala, Sweden. Inclusion criteria were diagnosis of pheochromocytoma or
paraganglioma confirmed by routine histopathological investigation. Tumour
specimens were dissected directly upon resection and snap frozen in liquid nitrogen.
Tissue samples were then stored in low temperature freezers that maintained an
average temperature of less than -69°C. Peripheral blood was collected at the time of
patient admission for surgery and stored below -20°C.
Sample preparation and nucleic acid extraction Tumour cell content was quantified by light microscopy that was performed by two
independent observers. Selected samples were macro-dissected in order to reduce the
proportion of non-tumour cells. RNA and Genomic DNA were extracted using
DNeasy Blood & Tissue and/or AllPrep DNA/RNA kits (Cat. No. 69506 and 80204,
Qiagen, Hilden, Germany) as instructed by the manufacturer. Reverse transcription
was performed using RevertAid First Strand cDNA Synthesis Kit (Thermo Scientific,
Waltham, MA, USA). Nucleic acid quality and concentrations were assessed using
Nanodrop spectrophotometer (ThermoFischer Scientific, MA, USA).
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Sample Sequencing
Targeted Deep SequencingGenomic DNA from 131 PPGL samples were analysed with targeted next generation
sequencing. For this purpose a a Truseq Custom Amplicon (Illumina Inc. CA. USA)
targeted enrichment kit was designed to cover the protein coding sequences of the
SDHA. SDHB. SDHC. SDHD. SDHAF2. VHL. EPAS1. RET (Exons 8. 10-11 and 13-
16). NF1. TMEM127. MAX and H-RAS (Exons 2 and 3) genes. Genomic enrichment
and library preparation experiments were performed by the SciLifeLab core facility
(http://molmed.medsci.uu.se/SNP+SEQ+Technology+Platform/) as instructed by the
manufacturer (Part# 15027983). The generated 175bp paired end libraries were
indexed. pooled and sequenced twice on a MiSEQ instrument (Illumina Inc) as
instructed by the manufacturer (Part# 15027617). Read mapping to the human
reference sequence HG19 and subsequent variant calling were performed using
MiSEQ Reporter v2.1.43 (Illumina Inc) using default settings. Briefly reads were
mapped using a Smith-Waterman algorithm (reference sequence HG19) and variant
called using the Genome Analysis Toolkit (GATK). Results from generated .bam
and .vcf files were further analysed and visualized using CLC Genomics Workbench
5.51 (CLCbio. Aarhus. Denmark). Variant were processed by (1); excluding variants
not available in both sequencing runs. (2); excluding synonymous variants without a
probable splice site effect. (3); annotation for overlapping information in; Single
Nucleotide Polymorphism database (dbSNP) build 137. Catalogue of Somatic
Mutations in Cancer (COSMIC) (1). database of Human Gene Mutation Data
(HGMD) (2) and Leiden Open (source) Variant Database (LOVD). The impact of
non-synonymous amino acid substitution was further assessed in silico using
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Polymorphism Phenotyping v2 (Polyphen2) (3) and Sorting Intolerant from Tolerant
(SIFT) (4). Variants were classified as Benign. Pathogenic or Unknown (Variant of
Unknown Significance. VUS). Variant frequencies were determined from .bam files
generated by MiSEQ Reporter v2.1.43 using the CLC Genomics Workbench 7.5
quality based variant calling algorithm (lower variant threshold 5%. default settings).
The mean of the variant frequencies generated in sequencing runs 1 and 2 were
calculated and used for further analysis.
Variants predicted as pathogenic were validated with sanger sequencing using
genomic DNA and cDNA when appropriate. Primer sequences can be obtained by
request.
PCR amplification. fragment separation and Sanger Sequencing. Variants located outside the targeted regions could cause truncation of the NF1
protein through aberrant RNA splicing (5) and selecting tumours with LOH
overlapping the NF1 locus have been shown to enrich for NF1 mutated tumours (5,
6).
Primer sequences of NF1 cDNA (NM_001042492.2) were obtained from Welander et
al. (5). Amplified PCR products were sequenced using automated Sanger sequencing
(Beckman Coulter genomics. Takeley. UK). PCR amplified cDNA from tumours and
three normal controls were separated on 2.5% agarose gel. Those in which alternative
lengths of amplicons could not be excluded samples were selected for sequencing.
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High throughput sequencing of selected PCR amplicons. Genomic DNA from the tumours of two patients were selected for additional
validation; patient 8 with a 30bp deletion that was not detected using TSCA libraries
and Patient 29 with low allele frequency. Both variants occurred in exon 1 of the VHL
gene and were amplified by PCR using custom primer sequences designed in house
using NCBI primer. Nextera (Illumina inc) paired end sequencing libraries were
prepared from 1 ng of amplified dsDNA using an enzymatic fragmentation approach.
Briefly amplified DNA was fragmented and tagmented by transposomes. A limited-
cycle PCR reaction amplified the insert DNA and added index sequences. The
libraries were purified using Ampure XP beads (Beckman coulter genomics. CA.
USA). normalized and pooled into a single suspension. The sample pool was
sequenced on a single sequencing run on the MiSEQ (Illumina Inc) instrument.
Library preparation and sequencing were performed by SciLifeLab core facility
(Stockholm node). Read mapping and variant calling were performed using CLC
Genomics Workbench 5.5 mapping algorithm and quality based variants caller with
default settings.
Semi-Quantitative PCR
Experiments were performed in triplicates using SsoAdvanced SYBR Green
Supermix (Bio-Rad laboratories, Hercules, CA, USA) on a CFX96 Real Time system
(Bio-Rad laboratories). Expression of VEGFA was analysed and normalized to
HPRT1 expression. ΔΔCT values were calculated for further analyses.
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SNP array genotyping and raw data analysis. Genomic DNA from a total of 138 tumour samples were analysed with Illumina
infinium dual flourencence Single Nucleotide Polymorphism arrays
HumanOmniExpressExome-8v1_A. Omni1-Quad or Omni2.5-Quad (Illumina. CA.
USA) containing 730’525. 1.140.419 and 2.379.855 probes respectively. DNA
amplification. tagging and hybridization were performed according to the
manufacturer’s instructions and scanned on a HiScanSQ instrument (Illumina). The
experiments were carried out at Science for Life Laboratory core facilities.
SNP&SEQ Technology Platform in Uppsala. Sweden
(http://molmed.medsci.uu.se/SNP+SEQ+Technology+Platform/) according to the
manufacturer’s guidelines. Generated fluorescent raw signals were imported into
Illumina BeadStudio (version 7.5 build 2011) software and normalized against
reference data (ICF) provided by the manufacturer. Nexus copy number beadstudio
plugin was used to export total relative fluorescent intensities (logR) as well as the
relative intensity (BAF) for each individual probe.
Pipeline for resolving absolute ploidy and purity in PheochromocytomaWe utilized a workflow consisting of multiple commercially and publicly available
bioinformatics suites and algorithms as outlined schematically in figure S1.
Determination of LogR intensities and B allele frequenciesFurther analysis of SNP array results were performed using Nexus 7.5 (Biodiscovery.
CA. USA). Briefly data was normalized for GC waves by array specific quantile
systematic correction algorithms that were provided by the manufacturer. A circular
binary segmentation algorithm SNP-RANK was used to call regions with copy
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number events and/or allelic imbalances (significance threshold 10-13). Samples with
Nexus QC score >0.13 were excluded. Marginal events (defined as <100 probes) were
excluded from further analysis in order to reduce false predictions. Generated
segments were reviewed by two independent observers and consensus was reached by
integrating LogR and BAF. BAF values <0.5 were transposed (to 1-BAF) and
homozygous SNP calls excluded. The median value was calculated from both the
upper and lower band. Segment coordinates and the corresponding median logR and
BAF (mean of the two bands) were then exported for further analysis.
Copy number classificationIn order to determine the underlying ploidy and clonal fraction of specific segments
we used a two-step approach. First all segments were analysed using a maximisation
of parsimony model. In regions where multiple different combinations of clonal
fractions and ploidy may explain the observed data the model assumes that the
solution with the smallest number of deviations from diploid have the highest
probability of being correct. Regions with no relative change in LogR and with BAF
0.5 were considered heterozygous copy number neutral (ploidy AB). Regions with
aberrant LogR/BAF calls were assigned classifications: relative decrease in logR and
BAF >0.54 (technical detection limit) were considered a heterozygous loss (ploidy
B/A) whereas a relative increase in logR and BAF >0.54 were considered as a copy
number gain (ploidy AAB/BBA). Segmentations showing decrease in logR with BAF
0.54 were considered a homozygous loss (ploidy 0). Increase in logR and BAF <0.54
were considered a balanced copy number gain (ploidy AABB). Segments with logR
of 0 and BAF >0.54 were considered as copy number neutral loss of heterozygosity
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(ploidy AA/BB). Ploidy classifiers A. B. AB. AAB. BAA. AABB will be denoted as
simple calls in the remains of this manuscript.
Determination of clonal proportionsPloidy and BAF values were used to calculate the proportion of cells (p) harbouring
the particular SCNA (7). Formula (1) was derived where (a) denotes ploidy of allele
A and (b) denotes ploidy of allele B.
(1) p= 1−2 BAF( BAF−1 )∗b+BAF∗a−2 BAF+1
Segments showing p=1 were considered germline events and were considered to be
outside of the scope of this manuscript and removed from the subsequent analyses.(8)
Inferring allele specific copy number status by establishing relationships between logR and absolute ploidyWe hypothesized that a minority of the generated segments could harbour complex
combinations of multiple different chromosomal aberrations with different clonal
fractions. In order to identify such segments we sought to compare each segment to an
empirical dataset. LogR and copy number have been previously described to have a
distinct relationship (9). We ruled that our dataset of segments would have the
robustness to generate a similar relationship. This was based on (I) the expected
robustness of the maximization of the theory of parsimony approach (especially as
majority of our samples had limited number of SCNA) and (II) the validation of our
results from copy number estimation provided by the existing literature.
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Absolute copy number for simple calls were calculated using ploidy and clonal
fraction in accordance with Formulae (2). CN represents the total copy number, p the
fraction of aberrant cells and Pt the ploidity of the segment.
(2) CN=2 (1−p )+ p∗Pt
For all individual samples LogR (X-axis) and copy number (Y-axis) were then plotted
to establish sample specific standard curves. Segments plotted as outliers on the
standard curve were excluded and the remaining values included for logarithmic
regression that was used to generate functions of the form shown in Formulae (3)
describing the relationship between Log R and total copy number. Similar array
specific curves were also produced using all the segments generated on a specific
array.
(3) LogR=A∗ln (CN )−B
For each sample the function from standard curve was used to calculate total copy
number from LogR for all segments. Allele specific copy number status of each
segment could then be estimated through multiplying the calculated total copy
number with the corresponding BAF in accordance with Formulae (4) and (5).
(4) CN A=(1−BAF )∗CN
(5) CN B=BAF∗CN
Allele specific copy number was then used to calculate the fraction of cells in the
sample carrying each aberration (clonal fraction) using Formulae (1.) For each
sample. the tumor purity was estimated to be equal to the highest clonal fraction of the
segments in the sample. Segments with clonal fraction within 10 percentage points of
the highest clonal fraction in a given sample were classified to be fully clonal while
segments with lower clonal fractions were considered to carry subclonal events.
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Results
Table S1. Sequence coverage of targeted NGS
MiSEQ batch
MiSEQ run
Coverage, mean number of
reads
Percentage of targets at X-fold coverage
1X 5X 10X 40X 80X
1 1 201.94 98.1 97.7 97.1 91.3 82.51 2 197.3 98.1 97.6 97.2 90.8 80.12 1 280.3 98.5 98.1 97.3 92.1 84.72 2 284.4 98.5 97.9 97.3 92.1 84.7
Supplementary Table 1Mean Coverage and percentage of targets with X-fold coverage from MiSEQ runs 1 and 2.
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Supplementary Figure 2Summary of the utilized sequencing workflow. All but one mutation previously
detected by Sanger sequencing could be confirmed. There were no additional variants
discovered neither in sequencing rounds number 2 or 3. Analysing the 30bp deletion
not detected by targeted NGS showed that this particular variant was located at the
overlap of two amplicons (data not shown) and could be validated using customized
enrichment. NEXTERA libraries and MiSEQ sequencing. In conclusion all variants
could be validated using two principally different sequencing chemistries.
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Supplementary Figures 3A-B
Sequencing reads and chromatograms from tumour and normal tissue showing (A)
validation of H-RAS, RET and VHL mutations. Figure 3B presents data from patient
29 that had previously been determined as wild type in the VHL locus by Sanger
Sequencing analysis. Targeted NGS detected a pathogenic VHL mutation c.[193T>G].
Multiple samples from geographically different regions from the same primary
tumour was analysed using Sanger sequencing revealing a secondary peak
corresponding to the mutated G. The mutation was validated to have a 14.6%
(sequence depth 58746) allele frequency using Nextera libraries sequenced on a
Miseq instrument.
Supplementary Figure 4Validation of NF1 mutations that was determined to cause a splice site disruption by
in silico analysis. cDNA from tumour tissue were amplified by PCR and separated on
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agarose gel that revealed aberrant fragments lengths for all three cases. Results were
validated by Sanger Sequencing that showed effect on protein structure: c.288+1G>T,
p.Arg69_Gly96del, c2252-2A>G, p.Gly751fs and c.4836-2delA, p.1613_1871del.
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SNP array GenotypingGenotyping was performed with a success rate (defined as a genotyping call rate of
>98% for individual SNPs) of 95%. Median quality score determined by Nexus Copy
number was 0.029 (range 0.1-0.015). A discrete asymmetry between the two
fluorescent dyes was observed. Increasing difference between the two bands
proportional to the distance from 0.5 were noted with the highest differences observed
when the bands were in proximity of 1 and 0. Normalization with established
bioinformatics scripts did not compensate for this asymmetry (10). The performance
of the workflow was tested using BAF derived from either the upper and lower bands
or from each individual single band only. BAF calculations from both bands were
considered to have the most robust performance and were selected for further
analysis.
Results and validation of absolute ploidy and clonal fractionsA total of 1191 segments were generated. 1064 affected one allele and 127 were bi
allelic. Absolute ploidy and purity of two samples could not be resolved even after
considering the interpretations generated by ASCAT and TAPS hence both samples
were excluded from further analysis. Sample and array specific curves were created
from the remaining samples and logarithmic regression was applied to generate
quantitative relationships between LogR and absolute copy number. A small number
segments were outliers and were classified to have unknown copy number state. The
remaining segments were plotted and the extracted function of the standard curve
were in line with that of previous studies (9).
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Supplementary Figure 5. Standard curve showing relationship between copy number
and Log R ratio generated by all segments included samples and arrays. Middle line
equals mean value. Coloured area denotes one standard error.
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Estimation of sample tumour cellularityCorrelation between the estimations of sample purity was found between study
workflow and ASCAT (figure S6. Pearson correlations test R=0.830). Compared to
ASCAT (considered as golden standard) the in house pipeline tended to overestimate
sample purity. Troubleshooting revealed that by analysing BAF derived from the
lower band only the study workflow showed a stronger correlation to ASCAT.
However as this increased the intra sample divergence of clonal fractions we decided
to use BAF derived from both bands. Histopathological investigation showed low
sensitivity to detect samples with low purity as determined from SNP array data
(Figure S7).
Supplementary Figure 6Correlation of study observations and ASCAT analysis in estimating the total fraction
of tumour cells within each individual tumour sample. ASCAT could not determine
the tumour purity for two samples. Pearson correlation test R=0.830.
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Supplementary Figure 7
Correlation of results from histopathological investigation and ASCAT in estimating
the total fraction of tumour cells. Pearson correlation test R=0.658.
Supplementary Figure 8
Correlation between TAPS and the study workflow in the estimation of clonal
fractions for specific segments. Data from sixteen samples were selected because of
high levels of aneuploidy and/or subclonal fractions in order to validate the study
workflow.
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Comparison of robustness of the determination of variant frequenciesOnly samples in which both SNP array and deep sequencing analysis had been
performed on the identical batch of genomic DNA were considered for integrative
analysis. In order to determine the overlap between the two methods we selected
variants present in dbSNP and plotted the corresponding variant frequency (VAF)
generated from deep sequencing to the median transposed BAF observed at the
corresponding location by SNP array. Pearson correlation test confirmed satisfactory
overlap between the two methods (Figure S9A. Pearson correlation R=0.945).
Relative differences between the two methods were plotted against deep sequencing
read coverage. As expected this confirmed that variants with high read coverage
showed less variability than its counterparts (Figure S9B).
Supplementary Figure 9A and B. (A) correlation of allele frequencies of germline
SNPs between SNP array and deeps sequencing methods. (B) relative difference
between SNP array and deep sequencing variant frequencies dependent on deep
sequencing read coverage.
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Determining clonal architecture from integrated data
Allele frequencies of a total of 58 pathogenic mutations were included for further
analysis. Ploidy and purity from overlapping SNP array segments were utilized to
calculate the expected variant frequency of somatic alleles in a scenario were the
pathogenic allele would be present in 100% of cells that harbour the specific
structural variation. The following formula was derived (2).
(2) f =p∗a/ (p∗(a+b)+(1−p)∗2)
(f) denotes the expected variant frequency. (p) proportion of cells harbouring
structural variation. (a) ploidy of allele A (pathogenic allele). (b) ploidy of allele B.
Numbers denotes ploidy calls of alleles A and B.
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Supplementary table 2. Statistical correlations
Mutation subgroup §
Germline or somatic
mutation §§Malignant §§
Laterality (right vs left) §§
Gender, §§
Size (≤60mm/>6
0mm) §§
Age (≤50y/>50
y) §§PCC vs PGL §
p=Tumour Cellularity Study observation 0.003 0.023 0.313 0.444 0.545 0.018 0.154 0.304 ASCAT <0.001 0.042 0.856 0.168 0.782 0.048 0.197 0.878Histopathology 0.006 0.031 0.019 0.301 0.738 0.173 0.546 0.877SCNA events, n 0.023 0.35 0.393 0.121 0.053 0.004 0.023 0.068SCNA fraction of the genome, % 0.415 0.415 0.844 0.907 0.031 0.360 0.072 0.062
Fraction of changes with subclonal status, %
0.923 0.075 0.957 0.343 0.297 0.081 0.107 0.916
Supplementary table 2. Patient statistics calculated from primary tumours
Table shows statistical calculations of mutation subgroup, malignant status and PCC or PGL type to genomic parameters. Tumour cellularity
analysed with the workflow of the current study and ASCAT workflows as well as that of histopathological examination was included. SCNA;
Somatic Copy Number Aberrations, PCC; Pheochromocytoma, PGL; Paraganglioma. §; Kruskal-Wallis test, §§ Mann-Whitney U test.
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Supplementary table 3. Statistics on a tumour lesions basisMutation
subgroup§ Malignant§§ PCC vs PGL§§
PTumour cellularity Study observation <0.001 0.198 0.146 ASCAT <0.001 0.234 0.705 Histopathology 0.002 0.142 0.609SCNA events, n <0.001 <0.001 0.036SCNA fraction of the genome 0.053 <0.001 0.892Fraction of changes with subclonal status 0.114 0.174 0.059
Supplementary Table 3. Statistics on a tumour lesion bases
Table shows statistical calculations of mutation subtype, malignant status and PCC or
PGL type to genomic parameters. Eighty different tumour samples were classified
accordingly to mutation subgroup into; 9 HRAS, 29 NF1, 20 RET and 22 VHL. There
were 35 samples from tumours classified as malignant and 99 from those classified as
non-malignant. One hundred and twenty three samples were derived from PCC and
12 from PGL. Tumour cellularity analysed with study workflow and ASCAT
workflows as well as that of histopathological examination was included. SCNA;
Somatic Copy Number Aberrations. PCC; Pheochromocytoma. PGL; Paraganglioma.
§; Kruskal Wallis Test. §§ Mann-Whitney U test.
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