An agent-based model of signal transduction in bacterial chemotaxis.

We report the application of agent-based modeling to examine the signal transduction network and receptor arrays for chemotaxis in Escherichia coli, which are responsible for regulating swimming behavior in response to environmental stimuli. Agent-based modeling is a stochastic and bottom-up approach, where individual components of the modeled system are explicitly represented, and bulk properties emerge from their movement and interactions. We present the Chemoscape model: a collection of agents representing both fixed membrane-embedded and mobile cytoplasmic proteins, each governed by a set of rules representing knowledge or hypotheses about their function. When the agents were placed in a simulated cellular space and then allowed to move and interact stochastically, the model exhibited many properties similar to the biological system including adaptation, high signal gain, and wide dynamic range. We found the agent based modeling approach to be both powerful and intuitive for testing hypotheses about biological properties such as self-assembly, the non-linear dynamics that occur through cooperative protein interactions, and non-uniform distributions of proteins in the cell. We applied the model to explore the role of receptor type, geometry and cooperativity in the signal gain and dynamic range of the chemotactic response to environmental stimuli. The model provided substantial qualitative evidence that the dynamic range of chemotactic response can be traced to both the heterogeneity of receptor types present, and the modulation of their cooperativity by their methylation state.

Interactive visualization of intercluster galaxy structures in the horologium-reticulum supercluster.

We present GyVe, an interactive visualization tool for understanding structure in sparse three-dimensional (3D) point data. The scientific goal driving the tool's development is to determine the presence of filaments and voids as defined by inferred 3D galaxy positions within the Horologium-Reticulum supercluster (HRS). GyVe provides visualization techniques tailored to examine structures defined by the intercluster galaxies. Specific techniques include: interactive user control to move between a global overview and local viewpoints, labelled axes and curved drop lines to indicate positions in the astronomical RA-DEC-cz coordinate system, torsional rocking and stereo to enhance 3D perception, and geometrically distinct glyphs to show potential correlation between intercluster galaxies and known clusters. We discuss the rationale for each design decision and review the success of the techniques in accomplishing the scientific goals. In practice, GyVe has been useful for gaining intuition about structures that were difficult to perceive with 2D projection techniques alone. For example, during their initial session with GyVe, our collaborators quickly confirmed scientific conclusions regarding the large-scale structure of the HRS previously obtained over months of study with 2D projections and statistical techniques. Further use of GyVe revealed the spherical shape of voids and showed that a presumed filament was actually two disconnected structures.