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Literature Mining and Systems Biology

Literature Mining and Systems Biology

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Literature Mining and Systems Biology

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  1. Literature Mining and Systems Biology Lars Juhl Jensen EMBL

  2. Why?

  3. Overview • Information retrieval: finding the papers • Entity recognition: identifying the substance(s) • Information extraction: formalizing the facts • Text mining: finding nuggets in the literature • Integration: combining text and biological data

  4. Status • IR, ER, and simple IE methods are fairly well established • Advanced NLP-based IE systems are rapidly being improved • Methods for text mining and text/data integration are still in their infancy

  5. Example Mitotic cyclin (Clb2)-bound Cdc28 (Cdk1 homolog) directly phosphorylated Swe1 and this modification served as a priming step to promote subsequent Cdc5-dependent Swe1 hyperphosphorylation and degradation

  6. Information retrieval • Ad hoc information retrieval • The user enters a query/a set of keywords • The system attempts to retrieve the relevant texts from a large text corpus (typically Medline) • Text categorization • A training set of texts is created in which texts are manually assigned to classes (often only yes/no) • A machine learning methods is trained to classify texts • This method can subsequently be used to classify a much larger text corpus

  7. Ad hoc IR • These systems are very useful since the user can provide any query • The query is typically Boolean (yeast AND cell cycle) • A few systems instead allow the relative weight of each search term to be specified by the user • The art is to find the relevant papers even if they do not actually match the query • Ideally our example sentence should be extracted by the query yeast cell cycle although none of these words are mentioned

  8. Automatic query expansion • In a typical query, the user will not have provided all relevant words and variants thereof • By automatically expanding queries with additional search terms, recall can be improved • Stemming removes common endings (yeast / yeasts) • Thesauri can be used to expand queries with synonyms and/or abbreviations (yeast / S. cerevisiae) • The next logical step is to use ontologies to make complex inferences (yeast cell cycle / Cdc28 )

  9. Document similarity • The similarity of two documents can be defined based on their word content • Each document can be represented by a word vector • Words should be weighted based on their frequency and background frequency • The most commonly used scheme is tf*idf weighting • Document similarity can be used in ad hoc IR • Rather than matching the query against each document only, the N most similar documents are also considered

  10. Document clustering • Unsupervised clustering algorithms can be applied to a document similarity matrix • All pairwise document similarities are calculated • Clusters of “similar documents” can be constructed using one of numerous standard clustering methods • Practical uses of document clustering • The “related documents” function in PubMed • Logical organization of the documents found by IR

  11. Text categorization • These systems are a lot less flexible than ad hoc systems but can attain better accuracy • Works on a pre-defined set of document classes • Each class is defined by manually assigning a number of documents to it • Method • Rules may be manually crafted based on a very small set of manually classified documents • Statistical machine learning methods can be trained on a large number of classified documents

  12. Example Mitotic cyclin (Clb2)-bound Cdc28 (Cdk1 homolog) directly phosphorylated Swe1 and this modification served as a priming step to promote subsequent Cdc5-dependent Swe1 hyperphosphorylation and degradation Hints in the text • Strong: Cdc28 and Swe1 (“cell cycle” and “yeast”) • Weaker: mitotic cyclin, Clb2, and Cdk1 ( “cell cycle)

  13. Machine learning • Input features • Word content or bi-/tri-grams • Part-of-speech tags • Filtering (stop words, part-of-speech) • Singular value decomposition • Training • Support vector machines are best suited • Choice of kernel function • Separate training and evaluation sets, cross validation

  14. Entity recognition • An important but boring problem • The genes/proteins/drugs mentioned within a given text must be identified • Recognition vs. identification • Recognition: find the words that are names of entities • Identification: figure out which entities they refer to • Recognition without identification is of limited use

  15. Example Mitotic cyclin (Clb2)-bound Cdc28 (Cdk1 homolog) directly phosphorylated Swe1 and this modification served as a priming step to promote subsequent Cdc5-dependent Swe1 hyperphosphorylation and degradation Entities identified • S. cerevisiae proteins: Clb2 (YPR119W), Cdc28 (YBR160W), Swe1 (YJL187C), and Cdc5 (YMR001C)

  16. Recognition • Features • Morphological: mixes letters and digits or ends on -ase • Context: followed by “protein” or “gene” • Grammar: should occur as a noun • Methodologies • Manually crafted rule-based systems • Machine learning (SVMs) • But what can it be used for?

  17. Identification • A good synonyms list is the key • Combine many sources • Curate to eliminate stop words • Flexible matching to handle orthographic variation • Case variation: CDC28, Cdc28, and cdc28 • Prefixes: myc and c-myc • Postfixes: Cdc28 and Cdc28p • Spaces and hyphens: cdc28 and cdc-28 • Latin vs. Greek letters: TNF-alpha and TNFA

  18. Disambiguation • The same word may mean many different things • Entity names may also be common English words (hairy) or technical terms (SDS) • Protein names may refer to related or unrelated proteins in other species (cdc2) • The meaning can be resolved from the context • ER can distinguish between names and common words • Disambiguating non-unique names is a hard problem • Ambiguity between orthologs can be safely be ignored

  19. Co-occurrence extraction • Relations are extracted for co-occurring entities • Relations are always symmetric • The type of relation is not given • Scoring the relations • More co-occurrences  more significant • Ubiquitous entities  less significant • Same sentence vs. same paragraph • Simple, good recall, poor precision

  20. Example Mitotic cyclin (Clb2)-bound Cdc28 (Cdk1 homolog) directly phosphorylated Swe1 and this modification served as a priming step to promote subsequent Cdc5-dependent Swe1 hyperphosphorylation and degradation Relations • Correct: Clb2–Cdc28, Clb2–Swe1, Cdc28–Swe1, and Cdc5–Swe1 • Wrong: Clb2–Cdc5 and Cdc28–Cdc5

  21. Categorization of relations • Extracting specific types of relations • Text categorization methods can be used to identify sentences that mention a certain type of relations • Filtering can be done before or after relation extraction • Well suited for database curation • Text categorization can be reused • High recall is most important • Curators can compensate for the lack of precision

  22. Relation extraction by NLP • Information is extracted based on parsing and interpreting phrases or full sentences • Good at extracting specific types of relations • Handles directed relations • Complex, good precision, poor recall

  23. Example Mitotic cyclin (Clb2)-bound Cdc28 (Cdk1 homolog) directly phosphorylated Swe1 and this modification served as a priming step to promote subsequent Cdc5-dependent Swe1 hyperphosphorylation and degradation Relations: • Complex: Clb2–Cdc28 • Phosphorylation: Clb2Swe1, Cdc28Swe1, and Cdc5Swe1

  24. An NLP architecture • Tokenization • Entity recognition with synonyms list • Word boundaries (multi words) • Sentence boundaries (abbreviations) • Part-of-speech tagging • TreeTagger trained on GENIA • Semantic labeling • Dictionary of regular expressions • Entity and relation chunking • Rule-based system implemented in CASS

  25. Semantic labeling • Gene and protein names • Cue words for entity recognition • Cue words for relation extraction Named entity chunking • A CASS grammar recognizes noun chunks related to gene expression:[nxgene The GAL4gene] Relation chunking • Our CASS grammar also extracts relations between entities:[nxexpr The expression of [nxgenethe cytochrome genes[nxpgCYC1 and CYC7]]]is controlled by[nxpgHAP1]

  26. [phosphorylation_activeLyn, [negation but not Jak2]phosphorylated CrkL] [phosphorylation_activeLyn, [negation but not Jak2] phosphorylated CrkL] [expression_repression_activeBtk regulates the IL-2 gene] [expression_repression_activeBtk regulates the IL-2 gene] [phosphorylation_activeLyn also participates in [phosphorylation the tyrosine phosphorylation and activation of syk]] [phosphorylation_activeLyn also participates in [phosphorylation the tyrosine phosphorylation and activation of syk]] [expression_repression_activeIL-10 also decreased [expression mRNA expression of IL-2 and IL18 cytokine receptors] [expression_repression_activeIL-10 also decreased [expressionmRNA expression of IL-2 and IL18 cytokine receptors] [phosphorylation_nominal the phosphorylation of the adapter protein SHC by the Src-related kinase Lyn] [phosphorylation_nominal the phosphorylation of the adapter proteinSHC by the Src-related kinaseLyn] [phosphorylation_nominalphosphorylation of Shc by the hematopoietic cell-specific tyrosine kinaseSyk] [phosphorylation_nominal phosphorylation of Shc by the hematopoietic cell-specific tyrosine kinase Syk] [dephosphorylation_nominal Dephosphorylation of Syk and Btk mediated by SHP-1] [dephosphorylation_nominalDephosphorylation of Syk and Btkmediated by SHP-1] [expression_activation_passive [expressionIL-13 expression] induced by IL-2 + IL-18] [expression_activation_passive [expressionIL-13 expression] induced by IL-2 + IL-18]

  27. Mining text for nuggets • New relations can be inferred from published ones • This can lead to actual discoveries if no person knows all the facts required for making the inference • Combining facts from disconnected literatures • Swanson’s pioneering work • Fish oil and Reynaud's disease • Magnesium and migraine

  28. Trends • Most similar to existing data mining approaches • Although all the detailed data is in the text, people may have missed the big picture • Temporal trends • Historical summaries • Forecasting • Correlations • “Customers who bought this item also bought …”

  29. Time

  30. Buzzwords

  31. Correlations • “Customers who bought this item also bought …” • Protein networks • “Proteins that regulate expression …” • “Proteins that control phosphorylation …” • “Proteins that are phosphorylated …” • Co-author networks

  32. Transcriptional networks 3592 79 32 83 Regulates Regulated P < 910-9

  33. Signaling pathways 3704 27 11 44 Phosphorylates Phosphorylated P < 210-7

  34. Integration • Automatic annotation of high-throughput data • Loads of fairly trivial methods • Protein interaction networks • Can unify many types of interactions • Powerful as exploratory visualization tools • More creative strategies • Identification of candidate genes for genetic diseases • Linking genes to traits based on species distributions