Section: New Results

Classification of diffusion dynamics from particle trajectories

Participants : Vincent Briane, Charles Kervrann.

In this study, we are currently interested in describing the dynamics of particles inside live cell. We assume that the motions of particles follow a certain class of random process: the diffusion processes. We have proposed a statistical method able to classify the motion of the observed trajectories into three groups: “confined”, “directed” and “free diffusion” (namely Brownian motion). This method is an alternative to the commonly used Mean Square Displacement (MSD) analysis. We assessed our procedure on both simulations and real cases; an example of confined diffusion is the Ornstein-Uhlenbeck process while an example of directed diffusion is the Brownian motion with constant drift. The method is currently applied to investigate membrane trafficking (Rab11/Langerin (see Fig. 10 ) and Rab11/TfR protein sequences) using the following procedure:

1. Tracking of particles with any competitive algorithm.

2. Statistical test /classification applied on tracks longer than ten time points.

3. Estimation of diffusion parameters (e.g. drift, diffusion, ...).

Each trajectory is labelled with the most likely process and the parameters of the underlying process are estimated. Future work will concern the detection of change of motion dynamic over time. Some results of our test on the Langerin protein sequence are shown in Fig. 10 .

Collaborator: Myriam Vimond (ENSAI Rennes).

Figure 10. Labelling of the dynamics of trajectories on the Langerin protein sequence (Courtesy of UMR 144 CNRS-Institut Curie and PICT IBiSA). We display only the trajectories appearing on the first 100 frames. The color code is red for directed Brownian, green for Ornstein-Uhlenbeck, blue for Brownian, cyan for motionless. Top panel is labelled with our test, bottom panel with the MSD method.