o

bub lab

e: gil.bub@mcgill.ca
p: 514 398 8148

Bub lab

e: gil.bub@mcgill.ca
p: 514 398 8148

Our aim is to understand the dynamics of excitable cell networks found in the heart and brain. A big part of the research program is to develop imaging and computational methods - in particular new microscopy modalities, analysis and simulation programs, optogenetic techniques, and new ultra-fast sensors - and use these tools to study complex cardiac and neuronal excitable systems. Research themes goes into detail on new imaging techniques ( instrumentation), the data we collect in cardiac tissues ( excitable systems), and how we can control cells in real-time ( optogenetics).

McIntyre Medical Building rm: 1128
3655 rue Sir William Osler
McGill University, Montreal, Canada, H3G 1Y6

affiliations:
Department of Physiology QLS CAMBAM Department of Physics Cell Information Systems

research themes

The lab works on several closely interrelated research themes. If you are interested in being involved as either undergraduate trainee, graduate student, or postdoc, please contact Dr Gil Bub (gil.bub@mcgill.ca).
instrumentation

Excitable cells in the heart and brain generate fast signals (action potentials) that have to be captured using specialized detectors at over a thousand frames per second. At the same time, the structure of these cells is complex, requiring high resolution detectors and advanced microscopy techniques. We're working on many technologies to help with these issues: two examples - temporal pixel multiplexing and remote focusing - are shown below.

Temporal pixel multiplexing (TPM) is an imaging method that embeds high speed information into still image frames. Camera chips have millions of pixels which integrate charge generated when light hits their surface over a set integration time. TPM controls the way individual pixels are exposed during a single frame to embed high speed information in static images. This allows a lower resolution high speed movie to be extracted, giving a high-res still and a high-speed movie in one shot.

The TPM prototype used a micro-mirror array (DMD) to selectively expose pixels. The blur in the high res image can be resolved into a moving ball after decoding. The queen isn't moving so she's captured at high resolution.

A cardiac cell is loaded with a calcium sensitive dye. A high resolution image is captured with the TPM prototype, which allows the pixel data to be re-arranged to show changes in cell calcium during an action potential.

The original TPM prototype was built using a micromirror array (similar to those used in many consumer overhead projectors) to control pixel exposure times in a off-the-shelf camera. We are now developing CMOS sensors that incorporate TPM technology at the pixel level. Unlike other imaging chips which store data every frame, TPM doesn't move data (or transfer charge) during acquisition allowing it to be extremely fast. Our new chips should be able to image activity at over a million frames/second.

Remote focusing is a microscopy technique, pioneered by Prof. Tony Wilson's Scanning Optical Microscopy group in Oxford, which allows tissue to be scanned in depth without moving the sample or the imaging objective. When combined with laser scanning two-photon microscopy, the technique allows capture of cell structure and function in living tissue.

Two-photon microscopy uses infrared lasers to image cells in living tissue. Many labs build their own setups allowing them to test new techniques. This is a high-speed remote focusing microscope currently under development.

Remote focusing can be used to measure cell structure in the heart. It does this by measuring two oblique images at 45 degrees to the image plane, and using the measured sarcomere angle to calculate the cell's orientation.

One of the main limitations of scanning microscopes is that they're slow as the laser has to visit each point in an image. We're developing new remote focusing microscopes which split the laser into many beamlets, so we can increase acquisition speed. The aim of this project is to be able to measure cell-cell communication in intact heart and brain tissues.

 
more TPM: see the Nature Methods paper, the original TPM pages, and articles in New Scientist & IO9 magazines.
more remote focusing: see Tony Wilson's group original PNAS paper and our Circ Res paper.
collaborators: Roger Light, Ed Mann, Bei Li, Alex Corbett , Leonardo Sacconi , Martin Booth, Tony Wilson
industry & licencing: Cordin Scientific Imaging, STFC, Oxford University Innovation.
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excitable systems

Excitable media are systems which have the ability to propagate signals spatially without damping. In the heart, waves of excitation synchronise cardiac muscle contraction with every heart beat, and changes in the spatial patterns of these waves cause potentially deadly arrhythmias. We study these waves using mathematical models, intact heart muscle and bioengineered sheets of tissue, using a variety of experimental techniques.

Isochronal map of spiral wave initiation in a cardiac monolayer. PNAS, 1998.

Cardiac monolayers are thin sheets of heart muscle tissue grown in a petri dish. After a short while in culture, cells form connections and can generate waves of excitation. These waves can propagate out from a initiating point (a target), or they can generate a re-entrant circuit, which often has a spiral shape. In the intact heart, re-entry and spiral waves of activation underly arrhythmias such as atrial tachycardia and ventricular fibrillation. Studying how these re-entrant waves are generated in monolayers increases our understanding of arrhythmias and could lead to new treatments. The lab grows these sheets from neonatal chick hearts or stem cells, and we also investigate co-cultures of neurons and myocytes.

Simulations: Target and spiral waves are seen in many physical excitable media due to the relatively simple rules that underpin the behaviour of connected cells, even though the physical processes that drive each system can be extremely complex. These rules can be coded into a simple discrete computer model called a cellular automata . You should see one in this page's background if your browser is running javascript. Although the model is simple, similar CAs are used to understand cardiac dynamics (e.g. see , and links below). More realistic models, which (unlike CAs) consist of systems of dozens of coupled partial differential equations , often show similar wave patterns of behaviour.

- Click here to control the CA -

  for more: the original excitable media pages, optical mapping database, the PNAS and PRL papers.
new software! Jakub Tomek's Ccoffinn Toolkit: paper and download:
collaborators: Leon Glass, Alvin Shrier , Emilia Entcheva , Kevin Webb, Rebecca Burton, Matt Daniels.
optogenetics

Nature Photonics, 2015.

The term optogenetics refers to a set of methods for controlling and imaging genetically modified living tissue with light. Optogenetics has revolutionised the neurosciences and now is becoming increasingly popular in other tissues. In close collaboration with Emilia Entcheva's COOL lab , we've been sensitizing cardiac monolayers to light and seeing how we can control their behaviour.

One goal is to use optogenetics to control macroscopic wave dynamics. Macroscopic excitation waves are found in chemical reactions, slime mold colonies, as well as cardiac and neuronal tissues. In cardiac tissue, the patterns formed by these waves are different in healthy and diseased states. The ability to control wave shape, direction and velocity in cardiac tissue would expose new research targets: for example, since conduction velocity variability often causes re-entrant waves, control of wave velocity allows us to test hypotheses on spiral wave formation in a precise way.

The animated image (top right) shows an example of chirality control (chirality refers to the spirals rotation direction). A spiral wave in a cardiac monolayer (green) is coaxed into rotating in the opposite direction by a projected (red) spiral. Chirality control allows us to observe how spirals respond to stimuli: in this case the new spiral meanders to a prefered location, suggesting that the spiral probes its environment.

Future projects include controlling sympathetic neurons in intact heart and co-cultures, and revisiting the many classical experiments done on light sensitive chemical systems.

  for more: the Nature Photonics paper and a review in the Journal of Physiology.
collaborators: Emilia Entcheva , Rebecca Burton, Elis Cooper, Leonardo Sacconi , and Alex Corbett .

papers

classes and teaching

Fall term: Mathematical Models in Biology (BIOL 309), and a module in Introduction to the Physical Biology of the Cell (BIOL 219).

A simple CCD simulator for Claire Brown's MLMC 2017 Microscopy Fundamentals course:
Implementations of a 1D CA and Conways Game of Life for Bio 309.
A HTML5 logistic map iterator, a webGL parameter space diagram of the sine map, and webGL cellular automata for Bio 309.

people

Interested in joining the lab? We're looking for physics / engineering students with an interest in instrumentation development.
researchers
current members:

Gil Bub (PI)
associate professor
Physiology Department
McGill University
p: 514 398 8148
Miguel Romero Sepulvida
Masters Student
Physiology Department
McGill University
co-supervised with Alvin Shrier
Adrienne Caldwell
Masters Student
Physiology Department
McGill University
co-supervised with Alvin Shrier
Khadi Diagne
Masters Student
Physiology Department
McGill University
co-supervised by Leon Glass
past members:

Jakub Tomek
DPhil student - graduated 2017
(supervised with Drs Rodriguez & Paterson)
DPAG
University of Oxford
web page

collaborators and support
updated: Jan 2017 gil.bub@mcgill.ca