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Prediction of Gene Expression in Yeast using Conserved Sequence Templates

Prediction of Gene Expression in Yeast using Conserved Sequence Templates. Derek Chiang & Alan Moses Molecular & Cell Biology, UCB Eisen Lab. PROBLEM. What information controlling gene expression is encoded in genome sequences?.

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Prediction of Gene Expression in Yeast using Conserved Sequence Templates

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  1. Prediction of Gene Expression in Yeast using Conserved Sequence Templates Derek Chiang & Alan Moses Molecular & Cell Biology, UCB Eisen Lab

  2. PROBLEM What information controlling gene expression is encoded in genome sequences? >Saccharomyces cerevisiae chr V CGTCTCCTCCAAGCCCTGTTGTCTCTTACCCGGATGTTCAACCAAAAGCTACTTACTACCTTTATTTTATGTTTACTTTTTATAGATTGTCTTTTTATCCTACTCTTTCCCACTTGTCTCTCGCTACTGCCGTGCAACAAACACTAAATCAAAACAGTGAAATACTACTACATCAAAACGCATATTCCCTAGAAAAAAAAATTTCTTACAATATACTATACTACACAATACATAATCACTGACTTTCGTAACAACAATTTCCTTCACTCTCCAACTTCTCTGCTCGAATCTCTACATAGTAATATTATATCAAATCTACCGTCTGGAACATCATCGCTATCCAGCTCTTTGTGAACCGCTACCATCAGCATGTACAGTGGTACCTTCGTGTTATCTGCAGCGAGAACTTCAACGTTTGCCAAATCAAGCCAATGTGGTAACAACCACACCTCCGAAATCTGCTCCAAAAGATACTCCAGTTTCTGCCGAAATGTTT Features?

  3. Gene Expression: Experiment

  4. Gene Expression: Mechanism Promoter Structure

  5. Conserved Sequence Rules Hidden Variables Sites S1, S2, …Positions P11, P12, …P21, P22, …

  6. Conserved Sequence Rules Hidden Variables Sites S1, S2, …Positions P11, P12, …P21, P22, … PRIORS from sequence conservation

  7. Conserved Sequence Rules S2 S1 Conserved Sequence Rules Hidden Variables Sites S1, S2, …Positions P11, P12, …P21, P22, … { S1 > 0; S2 > 0; min( | P1j – P2j | < 30 ) } j

  8. Conserved Word Pairs • Finding Conserved Words • Evaluate Word Pairs 1) Joint Conservation 2) Close Spacing • Validate with Gene Expression

  9. Finding Conserved Words • 3860 CLUSTALW alignments from MIT • Conserved wordCw Found in same position in 3+ genomes within 600 bp of gene start > MET28_YAP5 Scer AACCTAAAACCAAAAAAAA-A-AAATAAGTCACGTGCACT Spar AATAAAAAATAGACTAACA-A-ATTGCGGTCACGTGCACT Smik AATCCCAGGCCAAAAACCAGA-AATTGAGTCACGTGCAGT Sbay GTCACGTGCCCGACGGCCCCACAACTGTGGCATCCATCTT

  10. Conserved Word Pairs • Finding Conserved Words • Evaluate Word Pairs 1) Joint Conservation 2) Close Spacing • Validate with Gene Expression

  11. TEST: Joint Word Conservation Word 2 Conserved Y N S2 S1 Y Word 1 Conserved N

  12. TEST: Joint Word Conservation Y N Y 32 162 N 3226 134 Word 2 Conserved S2 S1 Word 1 Conserved Chi-square Test for Independence(Yates adjustment)

  13. TEST: Joint Word Conservation • 2090 words (Length 6: Word-Rev complement ) • 2.06  106 Word PAIRS (Exclude overlap) HISTOGRAM Empirical c20.005 = 30 Bonferroni c20.05 = 31 -log10( Frequency ) Yates adjusted c2

  14. TEST: Close Spacing For conserved genes g : 1 … N Jg = ( P1g, P2g ) sampled jointly from position distributions Test Statistic P1 P2 NULL: X obtained from random sampling ALT: Xsmaller than expected from sampling

  15. TEST: Close Spacing Nonparametric Bootstrap 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 Avg. Min. Distance X = 32 bp

  16. TEST: Close Spacing Nonparametric Bootstrap 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 7 8 2 4 1 6 3 5 2 3 6 8 1 4 7 5 Bootstrap Distance X*b = 65 bp

  17. TEST: Close Spacing • Position distributions P1 = { P11, … , P1v } P2 = { P21, … , P2w } • Data J1 = ( P11, P21 ), … , Jn = ( P1n, P2n ) • Bootstrap J1*b = ( P11*b, P21 *b ), … , Jn = ( P1n *b, P2n *b) resampled with replacement from P1, P2 • Record quantile of X in 100000 samples of X*b (empirical null distribution) Nonparametric Bootstrap

  18. TEST: Close Spacing HISTOGRAM of Bootstrap Quantiles for Word Pairs

  19. Conserved Word Pairs • Finding Conserved Words • Evaluate Word Pairs 1) Joint Conservation 2) Close Spacing • Validate with Gene Expression

  20. Validating Expression Subsets Conserved Sequence (SUBSETTING) Rules S2 Genome (6000 genes) S1 { S1 > 0; S2 > 0; min( | P1j – P2j | < d ) } ? j SUBSET (N genes) Assess gene expression

  21. Validating Expression Subsets Some Nonparametric Tests • Subset mean (Mann-Whitney) • Subset distribution (Kolmogorov-Smirnov) • Subset weighted correlation ( ? ) • Kernel density classification (Mixture of normals) • Find optimal word pair distance d* for each test …

  22. Validating Expression Subsets Kolmogorov-Smirnov Frequency log2(Gene expression)

  23. Conserved Word Pairs – EXAMPLES aa / N starv Cadmium Heat shock AACTGT-CACGTG (Cbf1-Met31) N 29Pair c2 55Spacing p 0.01 63 bp MET28_YAP5 189 bp YHR112C_YHR113 p < 10-7 p < 10-8

  24. Conserved Word Pairs – EXAMPLES Other DNA damage MMS AAACGA-CCGATA (Upc2-Hap1) N 32Pair c2 39.5Spacing p 0 34 bp 101 bp p < 10-5

  25. Pipeline Summary # Genes > 10 Spacing < 0.05 K-S < 10-5 & Improve > 10 Known TF

  26. Future Directions • Better gene expression subset tests (Timecourse) • More flexible sequence models (IUPAC, Self-dimer) • Automate distance cutoff (Distance d) • Parameter optimization: 8 threshold values!( Conserved: # aligned genomes & # upstream bp, Joint conservation c2, Bootstrap quantile, K-S probs, Min gene #, Distance d )

  27. Acknowledgements Michael Eisen Eisen Lab Justin Fay Audrey Gasch Hunter Fraser Venky Nandagopal Dan Pollard Ben Lewis

  28. Validating Expression Subsets Kolmogorov-Smirnov

  29. Comparing Expression Samples

  30. Comparing Expression Samples

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