MTtbox documentation

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Why?

The aim is to model the growth of microtubules (and other dynamic organelles such as actin). Organelles grow through chemical reactions and growing organelles can collide with other organelles and membranes. To address these two features we adopted a data structure that stores microtubules as a list of vertices each of which is associated with a volume. Volumes are represented by a three dimensional array (lattice) of voxels. Regions within this volume are designated by numerical labels, e.g. 0 for cytoplasm, -4 for plasma-membrane. The size of the entire volume determines the resolution of both the collision detection system and chemical reaction/diffusion system. Resolution increases with the number of voxels. Increasing the number of voxels decreases the speed of computation and increases the demand for memory (>=16 Gbytes memory is highly desirable).

Current Status

MTtbox is currently under test and further development
The main data structure is called: 'data'. It can be accessed from the Matlab command line by declaring data to be global.

global data

at any time. The following documentation will refer to fields in data. It also refers to the custom menu items by menu:name.

The MTtbox graphical user interface (GUI) was created using the rapid prototyping system: DArT_Toolshed\ToolBag\Demo of JRK GUI\GuiDemo.m. This uses a text file GuiDemoLayout.txt to specify the GUI. The GUI has a control panel (handle: data.PanelH) and a graphics panel (handle: data.plotprops.AxesH) The MTtbox control panel is specified by MTtboxLayout.txt.

First view of the MTtbox

1 A

The toolbox is launched with the command MTtbox Which will cause the interface to appear at the top left of the monitor. The left panel (accessed through the handle: data.PanelH) provides control and the right panel (data.plotprops.AxesH) displays the output. They can be dragged anywhere and returned to the top-left using menu:View:Controls to top-left.

1 B

A default project is created by selecting: menu:File:New Project It forms a cell bounded by regions labelled: Outside, cell_wall, plasma_membrane, cytoplasm and vacuole. These are concentric volumes. Length is measured in microns (time in seconds). The axis labels indicate the thickness of each layer in terms of voxels in this particular model. This is extremely low resolution - it means that the microtubules will have to be unrealistically large. This is convenient for debugging and illustrating the system but not for simulations. The outer surface of each region is coloured, e.g. (Fig. on right) the vacuole is yellow and the cytoplasm is pale green. The cell can be rotated etc. using the panels at the top of the display panel. Fig. below: all the regions have been hidden (uncheck each item in menu:View) and the mesh associated with the cytoplasm outer surface is displayed (check menu:View:Organelle meshes)

1 C

A project is saved by selecting: menu:File:Save as Having first saved a project a default Interaction Function is created by selecting Edit. A default project file contains lots of comments to provide help on how to develop the project. At present the Interaction Functions is not copied to the new project on each Save as command - this has to be done manually.

The default file is largely a copy of MTtbox_BoilerPlate.txt which should be updated to reflect the latest ideas on how to build the function. Initial MTtbox interaction function is shown here

Modifying a default model using the Graphical User Interface

2 A Changing organelles in the cell

menu:Organelles shows a list of organelles, check those that are required and then re-establish the working volumes (used for collision detection) by using menu:Prefs:Cell size and shape

2 B Some cell shapes that can be selected using menu:Prefs:Cell size and shape

A) Coarse resolution (15k voxels) cubic cell. B) Coarse resolution spherical cell. C) Coarse resolution brick shape. D) Medium resolution (1M voxels) sheet of cytoplasm with plasma-membrane on one side. Blue spots are new microtubules nucleated in the plane of the cytoplasm. (Black bar: 1 micron scale bar.) Yellow: vacuole, green: cytoplasm, orange: plasma-membrane, pink: cell-wall. The axis labels report the thickness of outer regions and the half thickness of the central region (e.g. vacuole).

menu:Prefs:Cell size and shape establishes the shape of the cell and the arrangement of static organelles. The data structure it creates underpins the collision detection system. Current data structures data.cellprops.Vol is a volume filled with labels (range 0 to -7) representing regions: not-cell, cell-wall, plasma-membrane, cytoplasm, vacuole, etc. It is re-formed whenever the cell is redefined with pushbutton Initialise. data.working.Vol is a copy of data.cellprops.Vol which also contains regions representing dynamic organelles (microtubules and actin). It is re-zeroed by Restart. There are further volumes that supplement these two that are used for collision detection. Individual microtubule regions are recorded in data.cellprops.microtubules.Vol each microtubule region is represented by a unique ID. Factors and their associated diffusion constants are represented by data.factorprops.Concentration data.factorprops.DiffusionConst each column of which represents a factor - they must be reshaped to the same format as the volume data.