System Biology  

Cell motility is a fundamental function for body formation and maintenance of life. We systematically investigate mechanisms of cell motility. We also develop a new microscope system, which enables us to observe intracellular ions and molecules and track the cell at the same time. High-speed visual feedback control is an efficient technique for cell tracking.

3D cell tracking and fluorescent microscope system

A fluorescent microscope is a useful tool to estimate intracellular ionic and/or molecular dynamics. However, most of fluorescent microscopes lack a cell tracking function. Therefore, a freely moving cell easily escapes from a scope and fluorescent observation is often finished.

To solve this problem, we developed a new fluorescent and tracking microscope system (Fig. 1A). By using the developed system, we could observe emission lights to estimate intracellular dynamics, and we could simultaneously observe a transmission light to control an electrical XYZ stage for 3D single cell tracking.

To evaluate a performance of the developed system, we demonstrated a continuous recording of intracellular Ca2+ concentration in a freely moving Paramecium multimicronucleatum over 1.5 minute (Fig. 1B). Indo-1 was used as a Ca2+ indicator.

Fig. 1 (A) Schematic architecture of a fluorescent and tracking microscope system. (B) Time lapse of intracellular Ca2+ concentration of a freely moving paramecium.

Our works: T. Obara, Y. Igarashi, D. Wako, H. Tsubokawa, Y. Nakaoka, and K. Hashimoto: "Fluorescent and tracking microscope system", Focus on Microscopy 2008, p. 23, 2008.

Parallel Implementation of Contour Detection of Paramecia by using CPV System

We propose a 2D microorganism tracking system using a parallel level set method and a column parallel vision system (CPV). This system keeps a single microorganism in the middle of the visual field under a microscope by visual servoing an automated stage. We propose a new energy function for the level set method. This function constrains an amount of light intensity inside the detected object contour to control the number of the detected objects. This algorithm is implemented in CPV system and computational time for each frame is 2 [ms], approximately. A tracking experiment for about 25 s is demonstrated. Also we demonstrate a single paramecium can be kept tracking even if other paramecia appear in the visual field and contact with the tracked paramecium.

Fig. 2 A continuous image sequence and zero level sets. Zero level sets, which are computed contours of our method, are drawn as white curves. A single paramecium is tracked to be in the middle of a visual field, even if another one swims into the visual field and contact with the tracked paramecium at 3000 ms.

Our works: X. Fei, Y. Igarashi, and K. Hashimoto:"2D tracking of a single paramecium by using a parallel level set and a visual servoing" IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM2008), pp. 27-32, 2008.