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Complex networks are found throughout biology
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Complex networks are found throughout biology

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  1. Complex networks are found throughout biology

  2. Can we define the basic building blocks of networks? Generalize the notion of MOTIFS, widely used in sequence analysis, to the level of networks. Sequence motif: a sequence that appears much more frequently than in randomized sequences. ‘Network motif’: a pattern that appear much more frequently than in randomized networks.

  3. X Y Z Database of direct transcription interactions in E. coli Transcription factors Directed graph X Y Z operons 424 nodes, 519 interactions Based on selected data from RegulonDB + 100 interactions from literature search Shen-Orr 2002, Thieffry Collado-Vides 1998

  4. Algorithm that finds n-node network motifs Examples of 3-node circuits N Find all n-node circuits in real graph X X X Y Y Z Y Z U X Z Y Z T M W And in a set of randomized graphs with the same distribution of incoming and outgoing arrows. Assign P-value probability of occurring more at random than in the real graph Randomization: Newman, 2000, Sneppen& Malsov 2002

  5. The thirteen 3-node connected subgraphs

  6. Two main types of feed-forward loops are found X X Y Y Z Z Incoherent Coherent

  7. Dynamics of the feed-forward loop system X(t) = time varying input dY / dt = F(X) – a Y dZ / dt = F(X) F(Y) – b Z F Mangan, PNAS, JMB, 2003 Threshold

  8. The feed-forward loop is a filter for transient signals allowing fast shutdown Mangan, PNAS, JMB, 2003

  9. GFP Reporter plasmid system for promoter activity Low copy plasmid Fast folding GFP Nontoxic Lutz, Bujard 1997 Zaslaver et al, Nat. Meth. 2006

  10. Construct strains, each reporting for a different promoter Plasmid with promoter for gene X controlling a reporter Gene X intact on chromosome High throughput cloning: Promoter PCR, restriction, ligation, preps all in 96-well format.

  11. Construct strains, each reporting for a different promoter Grow strains under same conditions and measure reporter fluorescence or luminescence Each well reports for a different promoter Commercial fluorimeter/luminometer shakes, temperature control, injectors. Measure at the same time cell optical density.

  12. Activity of 96 promoters across 20 h growth in 20 conditions 7 min resolution GFP/OD

  13. Day-day reproducibility of better than 10% GFP repeat 2 *2 *1.1 *0.9 *0.5 10% 2000 strains available Open BioSystems 2-fold GFP repeat 1

  14. Maximal response to a pulse of X is filtered by FFL Input pulse to X of duration T T Response X Z X Y Z Simulation Pulse duration T

  15. Sign-sensitive filtering by arabinose feed-forward loop Max response crp lacZ crp araC araB cAMP Pulse duration [min] Experiments: Mangan et al , JMB (2003).

  16. OFF pulse Feed-forward loop is a sign-sensitive filter Mangan et al JMB 2003

  17. Shen-Orr, et al Nature genetics 2002

  18. The single-input module can generate a temporal program of gene expression

  19. Flagella operons are activated in temporal order Kalir, Leibler, Surette, Alon Science 2001 Laub, McAdams, Shapiro Science 2000

  20. Temporal order matches position of proteins along the flagella motor

  21. Turn ON (arg removed) Turn OFF (arg added) Time [min] Time Temporal order in Arginine biosynthesis system with minutes between genes Zaslaver, Surette, Alon, Nature Genetics 2004

  22. Turn ON (arg removed) Turn OFF (arg added) Time [min] Time Temporal order matches enzyme position in the pathway Glutamate N-Ac-Glutamate N-Ac-glutamyl-p N-Ac-glutamyl-SA N-Ac-Ornithine Citrulline Arginine Klipp, Heinrich

  23. 199 4-node directed connected subgraphs

  24. 4-node motifs in E. coli network: overlapping regulation X X Y Y Z W Z2 Z1 Overlapping regulation Feed-forward loop with two output genes

  25. Hengge-Aronis

  26. Mapping Logic gates using GFP reporter arrays (LacZ) IPTG ANDGATE? LacZ cAMP Setty, Mayo, Surette, Alon, PNAS 2003

  27. Can we draw complex networks in an understandable way?

  28. X X X Y Y Y Z Z W Z2 Z1 E. coli and yeast transcriptional networks show the same motifs Feed-forward loop: coli 40, yeast 74, over 10 STDs from random networks! Same two types of FFLs. The same 4-node motifs Also SIMS and DORs The same network motifs characterize transcriptional regulation in a eukaryote and a prokaryote Milo et al 2002, Lee at al 2002

  29. The incoherent FFL can act as a pulse generator X Z Y Z Incoherent Type 1 FFL t Mangan et al, 2006 Basu et al, 2004

  30. Developmental transcription network made of feed-forward loops: B. subtilis sporulation X1 Y1 AND AND Z1 X2 Y2 AND R. Losick et al. , PLOS 2004 AND Z2 Z3

  31. Feed-forward loops drive temporal pattern of pulses of expression X1 Z Z3 Z1 Z2 Y1 AND AND Z1 X2 time Y2 AND AND Z2 Z3

  32. Bacteria Fruit-Flies Yeast sH Ime1 smo dnaK dnaJ Ime2 Ptc Mammals HSF1 NFkB HIF p53 hsp70 hsp90 IkB iNOS Mdm2 Negative feedback loop with one transcription arm and one protein arm is a common network motif across organisms x y

  33. Negative feedback in engineering uses fast control on slow devices. Heater Power supply Temperature slow Thermostat fast Engineers tune the feedback parameters to obtain rapid and stable temperature control

  34. Negative Feedback can show over-damping, damped or un-damped oscillations, depending on parameters

  35. Negative Feedback can show over-damping, damped or un-damped oscillations, depending on parameters Engineers usually prefer damped oscillations- fast response, not too much overshoot

  36. Negative Feedback can show over-damping, damped or un-damped oscillations, depending on parameters Engineers usually try to avoid parameters that give Undamped oscillations

  37. real-time proteomics in single living cells for p53-mdm2 dynamics 0.2Kb 1.2Kb 0.7Kb pMT-I p53 CFP Hygro 3.5Kb 15Kb 0.7Kb pMdm2 Mdm2 YFP Neo P53-CFP Mdm2-YFP p53-CFP and Mdm2-YFP fusion protein allow imaging of p53 and MDM2 protein in living cells G. Lahav

  38. Food webs represent predatory interactions between species Skipwith pond (25 nodes), primarily invertebrates Little Rock Lake (92 nodes), pelagic and benthic species Bridge Brook Lake (25 nodes), pelagic lake species Chesapeake Bay (31 nodes), emphasizing larger fishes Ythan Estuary (78 nodes) birds, fishes, invertebrates Coachella Valley (29 nodes), diverse desert taxa St. Martin Island (42 nodes), lizards Source: Williams & Martinez, 2000

  39. Foodwebs have“consensus motifs” • Consensus motifs – different from transcription networks • Feedforward is not motif - omnivores are under-represented

  40. Links between WWW Pages –a completely different set of motifs is found • WebPages are nodes and Links are directed edges • 3 node results

  41. Each node represents a transistor Each node represents a transistor motif: Logic gate Full reverse engineering of electronic circuit from transistor to module level Each node represents a gate motif: D-flipflop Each node represents a gate-flipflop motif: counter Itzkovitz 2004

  42. Map of synaptic connections between C. elegans neurons White, Brenner, 1986

  43. ASH Feedforward loops in C. elegans avoidance reflex circuit Nose touch Noxious chemicals, nose touch Sensory neurons FLP AVD Interneurons AVA Backward movement Thomas & Lockery 1999

  44. Networks can be grouped to super-families based on the significance profile Normalized Z-score Milo et al Science 2004

  45. Summary –network motifs Network motifs, significant patterns in networks Three motifs in transcription networks and their functions High-accuracy promoter activity measurements from living cells algorithms at Review: Nat. Rev. Gen. 2007

  46. Acknowledgments Weizmann Institute, Israel Alex Sigal Naama Geva Galit Lahav Nitzan Rosenfeld Shiraz Kalir Alon Zaslaver Erez Dekel Avi Mayo Yaki Setty Ron Milo Adi Natan Shmoolik Mangam Shalev Itzkovitz Nadav Kashtan M. Elowitz, Caltech S. Leibler, Rockefeller M.G. Surette, Calgary H. Margalit, Jerusalem

  47. Dynamics of the p53-mdm2 loop in single living cells, and the design principles of biological feedback Galit Lahav Uri Alon Weizmann Institute Israel