NASA satellite image strangeness

April 13, 2011 by · Leave a Comment 

I’ve set up a continuously updating satellite image of the earth as my gnome wallpaper. Every 3 hours it uses wget to ftp the latest image from world sunlight map over at die.net/earth. On Monday evening I noticed a strange artefact in the image. I haven’t noticed corruption in the images before but for a while there appeared to be a rather large contrail over north Australia:

If it’s a contrail it’s really big and really fast, not to mention covering several thousand miles. It’s most likely some glitch in the camera, but it doesn’t look like a digital error in the file.

I don’t know what it is. If anybody else does let me know.

XPPAUT

March 10, 2011 by · 10 Comments 

Recently, I’ve been playing about with some modelling tools but as time runs out it’s getting harder and harder to dedicate time to learning high level programming languages like Python and Matlab. I have recently made a return to xppaut, the X Windows interface to the famous AUTO package. At first, the software looks like it was built to control a 1957 nuclear power reactor, and it hasn’t really developed for the past 15 years. However, if it aint broke don’t fix it, and xppaut’s functionality still challenges the likes of Mathematica and Matlab. Copasi was initially conceived to supersede auto however despite it’s powerful parameter estimation and data fitting features Copasi still lacks some important features such as 3D plots, bifurcation and steady state analysis. After compiling the latest version 6.10 from source code on Linux I began wrestling with the interface, and made some progress with the example ode files. The interface is actually quite intuitive once you start using the keyboard shortcuts, and you can explore your models very quickly with a few key strokes. The operations are instantaneous and the software takes virtually no resources to run. The basic scripting language XPPAUT uses is very simple to build systems of ODE’s, as well as input mathematical formulas from text books and publications. You don’t require knowledge of the kinetics as you do for building reactions in Copasi. Once your model is in you can just button bash to start hunting out steady states and use various graphical trajectory tools. Within an hour or so of coffee and harsh language I made a plot of the Fitzhugh-Nagumo equations (a non-linear system used for modelling nerve conduction), added some Nullclines to find a fixed point, analysed it’s stability (finally understanding a bit of the mystery of eigenvalues) and plotted some field lines (a major achievement for a biologist!):
xppaut-interface

For the non-computer scientist / mathematicians, XPPAUT can provide some very fast results and give your matlab jedi colleagues a run for their money. There are a number of ODE solvers, including stochastic algorithms, and more advanced features include parameter fitting of experimental data using the Levenberg–Marquardt algorithm and even animations of your systems. Combined with Copasi’s range of parameter scanning and fitting features, these two tools are potentially very empowering for the biologists in systems biology. Personally, I think xppaut is much more diverse than Copasi, particularly the model script being able to input mathematical formulae, and I would have recommended it to our 1st year doctoral training program. The ability to visualize fixed points and watch the eigenvalues changing with the stability helped to understand this as a non-mathematician.

I’m off to find more Fitzhugh-Nagumo fixed points…

Update: For those interested in the software, there is an accompanying book: Simulating, Analyzing, and Animating Dynamical Systems by Bard Ermentrout which is really easy to read and goes through all the functions with worked examples and is clearly illustrated.

tired eyes

March 5, 2011 by · 1 Comment 

redshift logo
Growing time spent at the laptop have lead to increasing eye strain and migraine. This is just something a Ph.D student has to crack on with, however recently I’ve been experimenting with RedShift. Redshift is a handy Linux application that dynamically adjusts the screen’s colour temperature throughout the day to reduce the strain on the eyes as they fatigue. The software is inspired by f.lux which is available for Windows, Mac, and Linux, but Redshift attempts to improve on the Linux version a bit. At first it looks a bit pink, but after a few days (and particularly nights) I have experienced reduced pain after prolonged hours of reading journal articles and staring at maths.

Much recommended if you’re working the graveyard shift.

bedtime reading

March 3, 2011 by · Leave a Comment 

After our lab move we’re setting up from scratch. I was asked to provide a list of books that would be useful for new people to read in order to get an idea of modelling and systems biology. I thought I would put the list on here. I attempted to include a recommended levels of maths knowledge with each of the books. Beginner means you know basic high school maths. Intermediate means collage maths (A-Level), and advanced maths mean you like to self harm with numbers.

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SYSTEMS BIOLOGY
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An Introduction to Systems Biology: Design Principles of Biological Circuits – Uri Alon.

Very good book for all things systems and synthetic biology. Modelling genetic interactions, enzyme kinetics, metabolic networks etc. The maths in the examples is very difficult for non-mathematicians and there are no answers (I believe there is an answers book in preparation). Intermediate – advanced maths required.
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Systems Biology in Practice: Concepts, Implementation and Application – Edda Klipp

Written by mathematicians. This book covers all kinds of areas leading students as well as advanced researchers from different disciplines to an understanding of current ideas in the complex field of comprehensive experimental investigation of biological objects, analysis of data, development of models, simulation, and hypothesis generation. Advanced maths and some experience of systems biology literature required.
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Mathematical Models in Biology (Classics in Applied Mathematics) – Leah Edelstein-Kreshet

Very nice general book on modelling. Illustrated, well written, extensive examples. General biology (not exclusively molecular / microbiology). Written for mathematicians applying themselves to biology. Advanced maths required. A “nice to have” book.
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Systems Biology: Properties of Reconstructed Networks – Bernhard Palson.

Bernhard Palsson is a pioneer of systems biology with Hans Westerhoff. Very well written book. The book focuses on network interactions. Written for mathematicians and computer scientists who are modelling metabolic networks. Intermediate – Advanced maths required.

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Stochastic Modelling for Systems Biology – Darren James Wilkinson

This is the best book for stochastic modelling in systems biology. The book has a very good introduction but the chapters after are very complex for non-mathematicians. Concise and well written. Superhuman maths and statistics required.
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Simulating, Analysing, and Animating Dynamical Systems. A guide to XPPAUT for Researchers and Students. Bard Ermentrout.

This book describes how to set up and use the graphical modelling tool XPPAUT. AUT can be quite a tricky thing to use and this book attempts to teach you how to do it with simple explanation and worked examples. The book covers several concepts from the field of dynamical systems, including chaos theory, how systems depend on parameters, and how simple physical systems can lead to complicated behaviour.

XPPAUT is about 15 years old but is still more capable than many modern software packages like matlab and mathematica, and fills in gaps in the likes of Copasi with bifurcation analysis using AUTO.

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GENERAL MATHS
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Basic Mathematics for Biochemists – Athel Cornish Bowden.

Introductory text for biochemists who want to revise algebra, plotting, solving equations, differentiation and integration. Primer for undergrad biochemistry. Basic – intermediate maths required. Recommended text for biologists on the Manchester DTC systems biology program.
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Engineering Mathematics – K.A. Stroud

Excellent comprehensive maths book. Starts at basic working knowledge of maths and goes right up to M.Sc level.
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Choosing and Using Statistics: A biologists Guide. – Calvin Dytham.

The best introduction to statistics I’ve found. Written for students. Worked examples in minitab, excel and spss. No equations. Practical applications and worked examples. Good reference text.
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Lab Math: A Handbook of Measurements, Calculations and Other Quantitative Skills for Use at the Bench – Dany Spencer Adams.

Useful book for all the lab calculations that you should know… but don’t!

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That’s my list. If anybody has any other recommendations, let me know.

SB.OS

February 20, 2011 by · Leave a Comment 

sb.os logo
I was recently looking at combining some sbml model files together. You can do this in any text editor as sbml is just an xml flat file format (if that’s the correct terminology). Therefore, you could load each file into a text editor and cut and paste the components of the model. SBML however isn’t meant to be directly coded, and is more a method of transferring models between software tools. SBMLeditor however is a useful customized text editor for sbml files, and presents the file in a very visually accessible format. I haven’t got a great deal of experience of SBML however and no free time to go about editing big model files. I had a look on sbml.org and found semanticSBML; academic software designed for manipulating sbml models in a variety of ways. There’s a web based version as well as code that can be compiled locally on Windows and Linux. I attempted to install it on both operating systems but this was a bit of a nightmare. SymantecSBML also downloads a local copy of many databases such as chebi and kegg which makes the installation process very long and uses huge volumes of storage, and then ended with many errors for me. There’s a web based version using Java but this seems to not be running at the moment(?). I was about to take my usual approach to academic software and remove it when I happened upon SB.OS (“systems biology operational software”). SB.OS is a Ubuntu livecd containing many pre-installed systems biology tools, including symantecSBML. It’s a handy tool-kit to keep in your CD wallet. You can boot it up on any computer without installing anything, use the tools which are all pre-loaded, and not effect your primary operating system, making it excellent for the non-computer scientists like me. I fired up semanticSBML and had my models merged in a couple of minutes. SB.OS contains lots of tools from sbml.org including the systems biology workbench, SBMLeditor mentioned above, Taverna, Cytoscape and some simulators such as Cell Designer, Copasi, and XPPAUT. Hopefully it will continue to develop and update in the future.

PrimerPy

February 17, 2011 by · Leave a Comment 

I recently designed primers for my impending qPCR work. qPCR primers are typically shorter than normal PCR primers, with a higher melt temp and produce short 150-200bp amplicons. This requires some slightly different design than normal. There are infinite resources of information on designing primers for qPCR but I found PrimerPy a useful bit of software for mine. It’s free for use and open source, built using the Python programming language.
primerpy_interface
The current version uses Primer3 to do the calculations, optimized for SyBr green qPCR. I sent off my primers a couple of weeks ago and ran than them last week on the RotorGene and got a signal so they seem to be ok. Should be ready to go once the yeast get going.

PrimerPy is available to download here: http://code.google.com/p/oligobench/wiki/PrimerPy

stuck in a bad project

January 26, 2011 by · Leave a Comment 

God bless the Zheng Lab and their cheery lab monkeys. As I stare into the growing abyss each day this reminds me that dozens of other poor b******s do the same. God bless our PI’s.

parallel computing – biology style

January 25, 2011 by · Leave a Comment 

I’ve been reading Regot et al’s Nature paper, out last November which is very similar to my project. It’s very interesting if anybody is into building biological analogues of electrical circuits. The work by Regot, led by Ricard Solé and Francesc Posas at University Pompeu Fabra in Barcelona has used a distributed computing approach and built logic processing circuits as an emergent property of many cells working together with their own individual simpler circuits. I find this quite interesting as, as the author states, building complex circuits in single cell lines can be a complicated task. Many components must interact predictably and robustly within a complex matrix of pre-existing interactions that are poorly understood. Ron Weiss of MIT presented a workshop at FEBS in Alpbach 2 years ago and explained how he could build and model interactions between a promoter and a reporter gene, but going beyond 2 promoters the behaviour becomes almost completely unpredictable. There’s just too much stochastic noise and underlying lack of understanding of the cellular chassis (hence the push for Craig Venter’s synthetic cell) to build predictable and reliable behaviours that can be thoroughly characterised and remain stable over a prolonged time period. Using very simple interactions in individual cells is simple to build (theoretically!), and provides a library of simple constructs. These libraries can then be hot swapped (to use a computer geek term) with each other to make much more complex behaviours from the culture as a whole. This is a true combination of systems and synthetic biology. The individual circuits remain robust as they provide a lighter load on the cell line to maintain, and the emergent property subsequently remains robust (for >9h in the paper). The combinations can also be simulated and optimum mixtures designed for the desired circuit behaviour.

In systems as complex as yeast (compared with E. coli) this is a much more desirable framework to work, in my humble experience anyway. Libraries of strains can be collected and combined to explore complex behaviours or engineer interacting microbiomes with useful engineering applications like biosensing and biological computing. Previous papers in Nature to do with bio-computing have utilized RNA aptamers (e.g Win and Smolke, 2008) to enable switching on and off gene expression to replicate boolean logic, however RNA secondary structure can be difficult to predict, and can form many different conformations under different physiological conditions. Designing RNA aptamers can also be challenging, compared with cloning. One could imagine this leads to RNA aptamer structures being unstable or the results difficult to replicate across laboratories without highly skilled expertise. It is interesting to compare this kind of approach with using multi-cellular systems for biological computing.

I wonder if the type of systems being built by Ragot et al could combine eukaryotic and prokaryotic systems and exploit features of each, such as the fast growth of E. coli with the signal processing abilities of yeast. One could exploit the environmental robustness of Saccharomyces or Candida with motile prokaryotes etc. I imagine the growth cultures and the potential for each to attempt to out compete the other would be somewhat complex!

pressure

January 22, 2011 by · Leave a Comment 

pressure
Still no data from the lab, and many broken plasmids to sort out. Just ordered some additional components that will need to be investigated. They should arrive next week.

There is less than 10 months remaining to submission and many of my colleagues are sorting out their final experiments before beginning to write up. There’s no denying this project has been a disaster from start to finish. The months of lost time during the lab move compounded the problem, but I’m hoping to get something out of the new qPCR machine, couple it with some westerns, throw it in a model and get the hell out of dodge. I’m not sure if any Ph.D student has come this close to the wire, but it’s certainly an exercise in mental stability. If I can generate data by end of February then it should be a good stress reliever. Game on, I guess….

Python and Systems Biology

January 13, 2011 by · 3 Comments 

python logoRecently I’ve tried to pick up Python again as a generic programming language that I could use to do some modelling and supplement Copasi. Currently Copasi can’t do bifurcation analysis which I’ve been interested in using to explore models of MAP kinase cascades. I had a look at xppAut and worked through some tutorials, and also Matlab which is perfectly capable of doing this kind of analysis but I have always wanted to pick up a language that I could use to get a programming skills. Matlab’s code repository is comprehensive and pretty much anything you want to do has been done already, with infinite web site and forum discussions. Matlab however is BIG and challenges the bank account when not on an academic license. Python was mentioned at a few conferences in systems biology and many tools seem to be being developed with it and I had also used Python many years ago for data analysis so I had had some experience with it (I have no preference in particular for Python over Perl, Java, C, Fortran, or whatever, it just was going that way). Copasi also has Python bindings that enable you to script its functions and I thought I might be able to supplement Copasi’s simulators with additional features.

When I started my Ph.D many of the Python based systems biology tools were still emerging and I struggled to get them running, so I always defaulted back to Copasi or Matlab. There also weren’t many available other than scipy and numpy and the ODE integrators just didn’t compete with Matlab’s ODE45 (or I couldn’t seem to find ODE45 for Python). More recently however a number of tools have continued to develop and look very interesting.

I started up with the standard installation of python 2.6 in Ubuntu and added SciPy and NumPy from the repositories, with matplotlib. I then installed PySCes, Stompy, PyDSTools, and the Copasi language bindings.

PySces (Brett G. Olivier et al, Stellenbosch University) is a general toolset for all things to do with simulating cellular systems. It’s now compatible with SBML so I could import all the models I had built up in Copasi. (The process of exporting from Copasi to SBML and into PySCes however loses the names of all the species which is annoying in larger models). PySCes can do timecourse simulations with LSODA and CVODE, calculate steady state with HYBRD and NLEQ2, do MCA, structural analysis, bifurcation analysis with PITCON, and n dimensional parameter scans.

Stompy (Timo Maarleveld and B. G. Olivier, also Stellenbosch University) is in extension to PySCes that adds stochastic modelling to the above tools. It includes Direct, next reaction, and Tau leaping algorithms. Stompy can also plot the simulation output and do data analysis such as propensities, distributions, waiting times etc. The website includes a number of clear tutorials and is quite simple to use.

PyDSTool (Prof. Rob Clewley lab, Georgia State University) is another modelling toolbox with ODE/DAE/discrete map simulation tools, bifurcation analysis, symbolic expression utilities, and is compatible with SciPy and the SBML file format.

I’m not sure how much overlap there is between PySCes and PyDSTool in terms of functionality. I have not used either in great depth yet. PyDSTool has a nice tutorial for finding and investigating a bifurcation point.

Both tools appear to be being integrated into the graphical application Tinkercell (which also has a number of handy Python scripts for interrogating models of biological systems).

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