High Throughput Sequencing: Microscope in the Big Data Era

High Throughput Sequencing: Microscope in the Big Data Era
Sreeram Kannan and David Tse Tutorial ISIT 2014 Research supported by NSF Center for Science of Information. TexPoint fonts used in EMF: AAAAAAAAAAAAAAAA

DNA sequencing …ACGTGACTGAGGACCGTG CGACTGAGACTGACTGGGT
CTAGCTAGACTACGTTTTA TATATATATACGTCGTCGT ACTGATGACTAGATTACAG ACTGATTTAGATACCTGAC TGATTTTAAAAAAATATT…

High throughput sequencing revolution
tech. driver for communications Faster than Moore;s Law Implication to the IT community

Shotgun sequencing read

Technologies Sequencer Sanger 3730xl 454 GS Ion Torrent SOLiDv4
Illumina HiSeq 2000 Pac Bio Mechanism Dideoxy chain termination Pyrosequencing Detection of hydrogen ion Ligation and two-base coding Reversible Nucleotides Single molecule real time Read length bp 700 bp ~400 bp bp 100 bp PE 1000~10000 bp Error Rate 0.001% 0.1% 2% 10-15% Output data (per run) 100 KB 1 GB 100 GB 1 TB 10 GB

High throughput sequencing: Microscope in the big data era
Genomic variations, 3-D structures, transcription, translation, protein interaction, etc. The quantities measured can be dynamic and vary spatially. Example: RNA expression is different in different tissues and at different times. HTS as the 21st century microscope Pachter diagram

Computational problems for high throughput data
measure data manage utilize Assembly (de Novo) Variant calling (reference-based assembly) Compression Privacy Genome wide association studies Phylogenetic tree reconstruction Pathogen detection Engineering challenges to manage massive data sets: Compression for storage, communication and retrieval. Distributed processing and inference. Sampling data. Enable data-sharing across multiple organizations (hospital, insurances, pharma,…) Preserve privacy Information processing challenges to enable optimal decision making: Joint assembly and quantification across many high-throughput experiments. Dynamic model building and inference from high-dimensional data. Extract actionable information: alerts, waste reduction, monitoring effect of intervention… Modeling complex healthcare delivery systems (hospitals) as networks to enable data-driven scheduling, demand forecast, staffing, …. Scope of this tutorial

Assembly: three points of view
Software engineering Computational complexity theoretic Information theoretic

Assembly as a software engineering problem
A single sequencing experiment can generate 100’s of millions of reads, 10’s to 100’s gigabytes of data. Primary concerns are to minimize time and memory requirements. No guarantee on optimality of assembly quality and in fact no optimality criterion at all. Include a paper with many authors

Computational complexity view
Formulate the assembly problem as a combinatorial optimization problem: Shortest common superstring (Kececioglu-Myers 95) Maximum likelihood (Medvedev-Brudno 09) Hamiltonian path on overlap graph (Nagarajan-Pop 09) Typically NP-hard and even hard to approximate. Does not address the question of when the solution reconstructs the ground truth.

Information theoretic view
Basic question: What is the quality and quantity of read data needed to reliably reconstruct?

Tutorial outline De Novo DNA assembly. Reference-based DNA assembly.
De Novo RNA assembly

Themes Interplay between information and computational complexity.
Role of empirical data in driving theory and algorithm development.

Part I: De Novo DNA Assembly
TexPoint fonts used in EMF: AAAAAAAAAAAAAAAA

Shotgun sequencing model
Transition: have people thought about these basic questions before? Basic model : uniformly sampled reads. Assembly problem: reconstruct the genome given the reads.

A Gigantic Jigsaw Puzzle

Challenges Long repeats Read errors Human Chr 22
Plots of repeat statistcs Plot of errors Human Chr 22 repeat length histogram Illumina read error profile

Two-step approach First, we assume the reads are noiseless
Derive fundamental limits and near-optimal assembly algorithms. Then, we add noise and see how things change.

Repeat statistics harder jigsaw puzzle easier jigsaw puzzle
How exactly do the fundamental limits depend on repeat statistics?

Lower bound: coverage Introduced by Lander-Waterman in 1988.
What is the number of reads needed to cover the entire DNA sequence with probability 1-²? NLW only provides a lower bound on the number of reads needed for reconstruction. NLW does not depend on the DNA repeat statistics!

Simple model: I.I.D. DNA, G ! 1 normalized # of reads reconstructable
(Motahari, Bresler & Tse 12) reconstructable by greedy algorithm coverage 1 no coverage many repeats of length L no repeats of length L read length L What about for finite real DNA?

Example: human chromosome 22 (build GRCh37, G = 35M)
I.I.D. DNA vs real DNA (Bresler, Bresler & Tse 12) Example: human chromosome 22 (build GRCh37, G = 35M) data i.i.d. fit Can we derive performance bounds on an individual sequence basis?

Individual sequence performance bounds
(Bresler, Bresler, Tse BMC Bioinformatics 13) Given a genome s greedy deBruijn ML lower bound Lcritical simpleBridging Start with individual sequence, extract sufficient statistics, get curves repeat length multiBridging Lander-Waterman coverage Human Chr 19 Build 37

GAGE Benchmark Datasets
Rhodobacter sphaeroides Staphylococcus aureus Human Chromosome14 G = 4,603,060 G = 2,903,081 G = 88,289,540 What about the lower bound? multiBridging multiBridging lower bound multiBridging lower bound lower bound

Lower bound: Interleaved repeats
Necessary condition: all interleaved repeats are bridged. L m n In particular: L > longest interleaved repeat length (Ukkonen)

Lower bound: Triple repeats
Necessary condition: all triple repeats are bridged L In particular: L > longest triple repeat length (Ukkonen)

Individual sequence performance bounds
(Bresler, Bresler, T. BMC Bioinformatics 13) lower bound 4. Multibridging is the algorithm we propose, which is nearly optimal, at least for chromosome 19. Did we get lucky? length Lander-Waterman coverage Human Chr 19 Build 37

Greedy algorithm Input: the set of N reads of length L
(TIGR Assembler, phrap, CAP3...) Input: the set of N reads of length L Set the initial set of contigs as the reads Find two contigs with largest overlap and merge them into a new contig Repeat step 2 until only one contig remains

Greedy algorithm: first error at overlap
repeat contigs bridging read already merged A sufficient condition for reconstruction: Add some animations to illustrate the two extreme cases all repeats are bridged L

longest interleaved repeats
Back to chromosome 19 lower bound greedy algorithm non-interleaved repeats are resolvable! longest interleaved repeats at length 2248 longest repeat at GRCh37 Chr 19 (G = 55M)

Dense Read Model As the number of reads N increases, one can recover exactly the L-spectrum of the genome. If there is at least one non-repeating L-mer on the genome, this is equivalent information to having a read at every starting position on the genome. Key question: What is the minimum read length L for which the genome is uniquely reconstructable from its L-spectrum? Mention weight in L-spectrum

de Bruijn graph (L = 5) ATAGACCCTAGACGAT
AGCC AGCG GCCC GCGA CCCT CCTA CTAG ATAG CGAT AGAC ATAGACCCTAGACGAT Sreeram: Change figure 1. Add a node for each (L-1)-mer on the genome. 2. Add k edges between two (L-1)-mers if their overlap has length L-2 and the corresponding L-mer appears k times in genome.

Eulerian path (L = 5) ATAGACCCTAGACGAT Theorem (Pevzner 95) :
AGCC AGCG GCCC GCGA CCCT CCTA CTAG ATAG CGAT AGAC ATAGACCCTAGACGAT Sreeram: Change figure Theorem (Pevzner 95) : If L > max(linterleaved, ltriple) , then the de Bruijn graph has a unique Eulerian path which is the original genome.

Resolving non-interleaved repeats
Condensed sequence graph non-interleaved repeat Unique Eulerian path.

From dense reads to shotgun reads
[Idury-Waterman 95] [Pevzner et al 01] Idea: mimic the dense read scenario by looking at K-mers of the length L reads Construct the K-mer graph and find an Eulerian path. Success if we have K-coverage of the genome and K > Lcritical K-coverage condition and reads longer than L_ritical. Implies higher coverage than LW.

De Bruijn algorithm: performance
Loss of info. from the reads! greedy deBruijn lower bound 4. Multibridging is the algorithm we propose, which is nearly optimal, at least for chromosome 19. Did we get lucky? length Lander-Waterman coverage Human Chr 19 Build 37

Resolving bridged interleaved repeats
bridging read interleaved repeat Bridging read resolves one repeat and the unique Eulerian path resolves the other.

Simple bridging: performance
greedy deBruijn lower bound simpleBridging 4. Multibridging is the algorithm we propose, which is nearly optimal, at least for chromosome 19. Did we get lucky? length Lander-Waterman coverage Human Chr 19 Build 37

Resolving triple repeats
all copies bridged neighborhood of triple repeat triple repeat all copies bridged resolve repeat locally

Triple Repeats: subtleties

Multibridging De-Brujin
Theorem: (Bresler,Bresler, Tse 13) Original sequence is reconstructable if: 1. triple repeats are all-bridged 2. interleaved repeats are (single) bridged 3. coverage Necessary conditions for ANY algorithm: triple repeats are (single) bridged interleaved repeats are (single) bridged. coverage.

Multibridging: near optimality for Chr 19
greedy deBruijn lower bound simpleBridging 4. Multibridging is the algorithm we propose, which is nearly optimal, at least for chromosome 19. Did we get lucky? length multiBridging Lander-Waterman coverage Human Chr 19 Build 37

GAGE Benchmark Datasets
Rhodobacter sphaeroides Staphylococcus aureus Human Chromosome14 G = 4,603,060 G = 2,903,081 G = 88,289,540 Lcritical = length of the longest triple or interleaved repeat. What about the lower bound? Lcritical Lcritical Lcritical multiBridging lower bound multiBridging lower bound multiBridging lower bound

Gap Sulfolobus islandicus. G = 2,655,198 triple repeat lower bound
MULTIBRIDGING algorithm interleaved repeat lower bound

Complexity: Computational vs Informational
Complexity of MULTIBRIDGING For a G length genome, O(G2) Alternate formulations of Assembly Shortest Common Superstring: NP-Hard Greedy is O(G), but only a 4-approximation to SCS in the worst case Maximum Likelihood: NP-Hard Key differences We are concerned only with instances when reads are informationally sufficient to reconstruct the genome. Individual sequence formulation lets us focus on issues arising only in real genomes.

Confidence When the algorithm obtains an answer, can it be sure?
Under the dense read model, we can guarantee that when there is a unique Eulerian cycle, the reconstructed answer is correct. This happens whenever L > max(linterleaved, ltriple) Conversely, when L > max(linterleaved, ltriple), there are multiple reconstructions that are consistent with the observed data. Under the shotgun read model, there is ambiguity in some scenarios.

Read Errors ACGTCCTATGCGTATGCGTAATGCCACATATTGCTATGCGTAATGCGT T A T A C T T A Error rate and nature depends on sequencing technology: Examples: Illumina: 0.1 – 2% substitution errors PacBio: 10 – 15% indel errors We will focus on a simple substitution noise model with noise parameter p.

Consistency Basic question: What is the impact of noise on Lcritical? This question is equivalent to whether the L-spectrum is exactly recoverable as the number of noisy reads N -> 1. Theorem (C.C. Wang 13): Yes, for all p except p = ¾.

What about coverage depth?
Theorem (Motahari, Ramchandran,Tse, Ma 13): Assume i.i.d. genome model. If read error rate p is less than a threshold, then Lander-Waterman coverage is sufficient for L > Lcritical For uniform distr. on {A,G,C,T}, threshold is 19%. A separation architecture is optimal: error correction assembly

Why? noise averaging Coverage means most positions are covered by many reads. Multiple aligning overlapping noisy reads is possible if Assembly using noiseless reads is possible if M

From theory to practice
Two issues: Multiple alignment is performed by testing joint typicality of M sequences, computationally too expensive. Solution: use the technique of finger printing. 2) Real genomes are not i.i.d. Solution: replace greedy by multibridging.

X-phased multibridging
Lam, Khalak, T. Recomb-Seq 14 Prochlorococcus marinus Lcritical Substitution errors of rate 1.5 %

More results Prochlorococcus marinus Helicobacter pylori
Lcritical Lcritical Methanococcus maripaludis Mycoplasma agalactiae Lcritical Lcritical

A more careful look Mycoplasma agalactiae Lcritical-approx Lcritical

Approximate repeat example: Yersinia pestis
exact triple repeat, length 1662 5608 approximate triple repeat length

Application: finishing tool for PacBio reads
PacBio Assembler HGAP raw_reads.fasta contigs.fasta Our finishingTool raw_reads.fasta contigs.fasta improved_contigs.fasta

Experimental results Before After Escherichia coli Meiothermus ruber
Pedobacter heparinus

More detail of the result
Species Before [Ncontigs] After [Ncontigs] % Match with reference Time Size Escherichia coli (MG 1655) 21 7 [finisherSC] 99.60 < 3 mins (laptop) ~ 4.6M Meiothermus ruber (DSM 1279) 3 1 99.99 < 1 min (laptop) ~ 3.0M Pedobacter heparinus (DSM 2366) 18 5 99.89 < 3 mins ~ 5.1M S_cerivisea (fungus) 252 78 [finisherSC] 95.46 < 3 hours (laptop) ~ 12.4M S_cerivisea (fungus) 55 [Greedy] 53.91

Part II: Reference-Based DNA Assembly
(Mohajer, Kannan, Tse ‘14) TexPoint fonts used in EMF: AAAAAAAAAAAAAAAA

Many genomes to sequence…
100 million species (e.g. phylogeny) 7 billion individuals (SNP, personal genomics) … but not all independent 1013 cells in a human (e.g. somatic mutations such as HIV, cancer) courtesy: Batzoglou

Reference Based Assembly: Formulation
ACGTCCCATGCGTATGCATAATGCCACATATGGCTATGCGTAATGAGTACC Target ACGTCCTATGCGTATGCGTAATGCCACATATTGCTATGCGTAATGCGTACC Side Information Assembler

Types of Variations Substitutions (Single Nucleotide Polymorphisms: SNP) Reference ACGTCCCATGCGTATGCATAATGCCACATATGGCTATGCGTAATGAGTACC Target ACGTCCTATGCGTATGCGTAATGCCACATATTGCTATGCGTAATGCGTACC

Types of Variations Small Indels (Insertions and Deletions) Reference
ACGTCCATGCGTATGCTAATGCCACATATTGAGCTATGCGTAATGCTGTACC ACGTCC___ATGCGTATGC_TAATGCCACATATTGAGCTATGCGTAATGCTGTACC Target ACGTCCTAGATGCGTATGCGTAATGCCACATATGCTATGCGTAATGGTACC ACGTCCTAGATGCGTATGCGTAATGCCACATAT___GCTATGCGTAATG__GTACC

Types of Variations Structural Variation Reference Inversion
Duplication Duplication (dispersed) Copy Number Variation

Mathematical Formulation
Focus on SNP version Define SNP rate Noiseless reads What is Lcritical for this problem? Want exact reconstruction Algorithm r (Reference DNA) SNP Rate Reads from target t Estimate of Target DNA Dense

Mathematical Formulation
For any given reference DNA and SNP rate, what is the read length required for reconstruction? In the worst case among target DNA sequences Lcritical is a function of r, SNP rate Dense Reads from target t r (Reference DNA) Algorithm Estimate of Target DNA SNP Rate

Necessary Conditions Let the reference DNA have a repeat of size lrep > 2L r lrep lrep Consider two possible target DNA sequences t1 and t2 L L t1 t2 Since L < lrep /2, the two targets D1 and D2 indistinguishable from reads Sanity check: interleaved repeat of length lrep /2 in D1 and D2

Necessary Conditions Let the reference DNA have an approximate repeat of size lrep,app > 2L r Can create r’ close to r but having exact repeat of size lrep,app r’ t1 t2 If L < lrep,app / 2: the two possible targets t1 and t2 indistinguishable Tolerance for approximate repeat depends on SNP rate

Algorithm lrep,app lrep,app r t Map reads to r
Let L > lrep,app / 2 t Map reads to r Keep only uniquely mapped reads Estimate t r ť

Condition for Success Loci covered by uniquely mapped reads are correctly called. Algorithm fails at a particular locus => None of the (L-1) possible reads uniquely mapped 2L 2L Case 1 Case 2 r Second case more typical in real genome => 2L length approximate repeat in r L > lrep,app / 2 => The algorithm succeeds. Tolerance for approximate repeat depends on SNP rate

Assembly Vs. Alignment: I
Necessary condition L ≥ lrep,app (r) / 2 Sufficient condition L > lrep,app (r) / 2 (subject to the assumption) => Alignment near optimal and Lref = lrep,app (r) / 2. De Novo algorithm achieves Lcrit (t) = max {linterleaved(t), ltriple(t) } In terms of r, for worst case t Lde-novo = max {linterleaved,app (r), ltriple,app (r)} Tolerance for approximate repeat depends on SNP rate

Assembly Vs. Alignment: II
Clearly Lde-novo ≥ Lref since Lref is necessary. Lde-novo = max {linterleaved,app (r), ltriple,app (r)} ≤ lrep,app(r) = 2 Lref Thus gain from reference is at-most a factor of 2 in the read length. The maximal gain happens when linterleaved,app (r) = lrep,app (r), i.e., when the largest approximate repeat is an interleaved repeat. This happens for example, when the DNA is an i.i.d. sequence Tolerance for approximate repeat depends on SNP rate

Reference based Assembly: Reprise
Complexity of alignment Very fast aligners using fingerprinting available when SNP rate small Better than alignment ? Theory shows alignment near optimal But alignment is what everyone uses anyway Nothing better is possible? The limitations of the worst case formulation! If we adopt a individual sequence analysis for both reference and target, better solution possible.

Part III: RNA (Transcriptome) Assembly
Kannan, Pachter, Tse Genome Informatics ‘13 TexPoint fonts used in EMF: AAAAAAAAAAAAAAAA

RNA: The RAM in Cells transcription translation
The instructions from DNA are copied to mRNA transcripts by transcription RNA transcripts captures dynamics of cell RNA Sequencing: Importance Clinical purposes Research: Discovery of novel functions Understanding gene regulation Most popular *-Seq DNA RNA Protein transcription translation

Alternative splicing DNA Exon Intron RNA Transcript 2 RNA Transcript 1
AC TGAA AGC DNA ATAC GAAT CAAT TCAG Exon Intron 1000’s to 10,000’s symbols long ATAC CAAT TCAG GAAT TCAG RNA Transcript 1 RNA Transcript 2 Alternative splicing yields different isoforms.

RNA-Seq Reads ATAC CAAT TCAG TCA ATAC CAAT TCAG GAAT TCAG ATT GAAT
(Mortazavi et al, Nature Methods 08) Reads ATAC CAAT TCAG TCA ATAC CAAT TCAG Assembler reconstructs GAAT TCAG ATT GAAT TCAG GAA GAAT TCAG Existing Assemblers Genome guided: Cufflinks, Scripture, Isolasso,.. De novo: Trinity, Oasis, TransAbyss,…

RNA Sequencing: Bottleneck
Popular assemblers diverge significantly when fed the same input 24243 7553 9741 6457 448216 59647 5588 IsoLasso Scripture Cufflinks Is the bottleneck informational or computational or neither? Source: Wei Li et al, JCB 2011, Data from ENCODE project

Informational Limits Lcritical for transcriptome assembly No algo. can
Read Length, L Lcritical No algo. can reconstruct Proposed algo. can reconstruct in linear time On many examples, these two bounds match, establishing Lcritical ! Mouse transcriptome: Lcritical = revealing complex transcriptome structure What can we do at practical values of L?

Near-Optimality at Practical L
Fraction of Transcripts Reconstructable Read Length Read Length

Fraction of Transcripts Reconstructable Upper bound without abundance Upper bound on any algorithm Upper Bound Read Length Read Length

Fraction of Transcripts Reconstructable Proposed Algorithm Read Length Read Length

Necessity of Abundance Information
Fraction of Transcripts Reconstructable Upper bound without abundance Upper bound without abundance diversity Read Length Read Length

Transcriptome Assembly: Formulation
M transcripts s1,..,sM with relative abundances α1,..,αM which are generic (rationally independent). Dense read model: Look at Lcrit Get all substrings of length L along with their relative weights . s1 s2 sM α1 α2 αM α1+α2 αM

What is Lcritical for transcriptome?
Lcritical is lower bounded by the length of the longest interleaved repeat in any transcript It can potentially be much larger due to inter-transcript repeats of exons across isoforms. ATAC CAAT TCAG GAAT TCAG

The Information Bottleneck
s1 s3 s4 s2 s5 s1 s3 s4 s2 s5

s4 s4 s1 s3 s1 s3 s5 s5 s2 s3 s2 s3

s5 s1 s3 s2 s4 s5 s1 s3 s4 s2 s3 Unless L > s3 these two transcriptomes are confused

s1 s3 s4 s5 s1 s3 s4 s2 s2 s3 s5 Sparsity can help rule out this four transcript alternative But first two possibilities still confusable unless L > s3

How to Distinguish the Two

lymphoblastoid cell line
Abundance diversity lymphoblastoid cell line Geuvadis dataset

Abundance Diversity s4 s1 s3 s5 s1 s3

Abundance Diversity s5 s4 s1 s3 s1 s3 s5 s4 s1 s3 s1 s3 This transcriptome is not a viable alternative (non-uniform coverage) Even if L < s3 these transcriptomes are distinguishable.

Fooling Set under Abundance Diversity
a+c b-c Fooling Set under Abundance Diversity a s1 s2 s3 s1 s2 s4 b s4 s5 s2 s3 c These two transcriptomes are still confusable if L < s2

Achievability: Algorithm
From the reads we construct a transcript graph 0.1 Reads ATCCA ATCCA GATTC GATTC ATTCG ATTCG 0.3 0.3 TCCAT TCCAT 0.3 0.3 CCATT CATTC CATTC Weight edges based on relative frequencies

From the reads, we construct a transcript graph 0.1 Reads ATCCA GATTC ATTCG 0.3 0.3 TCCAT 0.3 0.3 CCATT CATTC Weight edges based on relative frequencies

From the reads, we construct a transcript graph 0.1 Reads ATC GAT TCG 0.3 0.3 CAT Weight edges based on relative frequencies

Transcripts from Graph
Paths correspond to transcripts Naïve Algorithm: Output all paths from the graph GAT TCG GAT 0.1 ATC TCG 0.3 0.3 CAT ATC CAT TCG

Utility of Abundance Consider the following splice-graph
Not all paths are transcripts Node frequencies give abundance information First idea: Use continuity of copy counts 0.12 s1 s3 s4 s1 0.12 s4 0.12 s3 0.88 s2 0.88 0.88 s5 s2 s3 s5

Utility of Abundance: Beyond Continuity
s0 s3 s4 5 More complex splice graphs: s0 s3 s5 s0 s1 s3 s4 s5 12 9 5 7 s2 6 s6 15 7 9 s1 s3 s6 6 s2 s3 s6 In general, we are given values on nodes /edges. Need to find sparsest flow (on fewest paths).

General Splice graphs Principle for general splice graphs:
Find the smallest set of paths that corresponds to the node / edge copy counts Network routing, snooping, societal networks How to split a flow? Edge-flow: Flow value on each edge (satisfying conservation) Path-flow: Flow value on each path Given a edge-flow, find the sparsest path flow 0.12 s1 s4 0.12 0.12 0.12 0.12 Start End s3 0.88 s2 0.88 0.88 s5 0.88 0.88

Sparsest Flow Decomposition
Problem is NP-Hard. [Vatinlen et al’ 08, Hartman et al ’12] Closer look at hard instances: most paths have same flow Equivalent to: Most transcripts have same abundance (!) This is not characteristic of the biological problem Our Result: Assume that abundances are generic Propose a provably correct algorithm that reconstructs when: L > Lsuff Algorithm is linear time under this condition Approximately satisfied by biological data !

Iterative Algorithm The algorithm locally resolves paths using abundance diversity Error propagation? Decompose a node only when sure If unsure, decompose other nodes before coming back to this node The algorithm solves paths like a sudoku puzzle Solving one node can help uniquely resolve other nodes! Can analyze conditions for correct recovery L > Lsuff

Algorithm: Example Run
4 6 7 a+b a b 3 5 1 2 b+c c 4 6 7 a+b a b 3 5 1 2 b+c c 46 47 a b 3 5 1 2 b+c c 46 47 a b 3 5 1 2 b+c c 1346 235 2347 a b c 346 35 a c 1 347 b 2

Practical Implementation
Multibridging to construct transcript graph Condensation and intra-transcript repeat resolution Identify and discard sequencing errors Aggregate abundance estimation Node-wise copy count estimates Smoothing CC estimates using min-cost network flow Transcripts as paths Sparsest decomposition of edge-flow into paths Deals with inter-transcript repeats

Practical Performance
Simulated reads from human chromosome 15, Gencode transcriptome Hard test case 1700 transcripts chosen randomly from Chr 15 Abundance generated from log-uniform distribution Read length=100, 1 Million reads 1% error rates Single-end reads / stranded protocol

Practical Performance
Fraction of Transcripts Missed False Positives Coverage Depth of Transcripts

Complexity Sparsest flow problem known to be NP-Hard
Can show using similar reduction that RNA-Seq problem under dense reads is also NP-Hard, assuming arbitrary abundances Reasons why our formulation leads to poly-time algorithm: Our assumption that abundances are generic Only worry about instances where there is enough information Individual sequence formulation lets us focus on issues arising only in real genomes.

Confidence Can we be sure when the produced solution is correct?
Assume dense read model We are finding the sparsest set of transcripts that satisfy the given L spectrum Under the assumption of genericity Theorem: If the sparsest solution is unique, then it is the only generic solution satisfying the L-spectrum (!) s1 s2 s3 s4 s5 0.12 0.88

Summary An approach to assembly design based on principles of information theory. Driven by and tested on genomics and transcriptomics data. Ultimate goal is to build robust, scalable software with performance guarantees.

Problem Landscape measure manage utilize data Assembly (de Novo)
Noisy reads RNA: Finite N Variant calling (reference-based assembly) Indels Large variants Metagenomic assembly Genome wide association studies Information bounds Phylogenetic tree reconstruction Pathogen detection Compression Compress memory? Privacy Information theoretic methods? Engineering challenges to manage massive data sets: Compression for storage, communication and retrieval. Distributed processing and inference. Sampling data. Enable data-sharing across multiple organizations (hospital, insurances, pharma,…) Preserve privacy Information processing challenges to enable optimal decision making: Joint assembly and quantification across many high-throughput experiments. Dynamic model building and inference from high-dimensional data. Extract actionable information: alerts, waste reduction, monitoring effect of intervention… Modeling complex healthcare delivery systems (hospitals) as networks to enable data-driven scheduling, demand forecast, staffing, ….

Acknowledgements DNA Assembly RNA Assembly Abolfazl Motahari Sharif
Soheil Mohajer Guy Bresler MIT Lior Pachter Berkeley Ma’ayan Bresler Berkeley Joseph Hui Berkeley Kayvon Mazooji Berkeley Eren Sasoglu Ka Kit Lam Berkeley Asif Khalak Pacific Biosciences

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