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Reports on Overseas' Conferences and Meetings
Report on the 9th International Microbeam Workshop

Keiji Suzuki, Department of Molecular Medicine

An international workshop on Microbeam experiments was organized in Darmstadt Technical University in Germany between July 15 and 17, 2010. This workshop was held every two years, and the last one was done in National Institute of Radiological Research, Chiba. This time, Prof. Marco Durante from GSI, organized 3-days' workshop. Approximately 100 scientists, including biologists, physicists, and mathematicians from all over the world came together. To my surprise, half of them were young scientists or PhD students.

The first half of the workshop was focused on the development of new microbeam facilities. Although more than 45 plans in all over the world were announced during the last meeting, and many of them have already started microbeam irradiation. The uniqueness of these newly developed devices was the beam quality, beam size, and particle species. For example, heavy-ion beam facility in GSI is now able to accelerate really heavy ions like U. Microbeam facility in Columbia University can now target submicron area. While these new beam lines were filled with future applications, the lack was its goal and the biological experimental designs. Thus, even though the physics has sufficiently forwarded in such facilities, the biology has failed to catch its progress.

The second day focused on the biological effects by targeted irradiation. Unique studies have been done in microbeam facility that have already been established. In the last meeting in Chiba, we did serious discussions on whether bystander effects were in deed induced by targeted irradiation or not. However, this time, such discussion has never been taken place. There seems to be a general consensus that bystander effects are not always necessary to be detected. It is expressed in certain combination of cells and culture conditions. Until now, several bystander factors have been listed, and most of them were cytokines, which requires membrane receptors to execute cellular response. Thus, it has been considered that a manifestation of bystander effects is partially dependent on the expression of such receptors. The points remained to be discussed include its physiological significance in tissues or organs, whose discussion needs unique experimental system using 3D-cultured cells.

During the meeting there were a couple of talks deal with 3D-cultured cells. As X-ray microbeam can not be used for this purpose because of its low energy penetration, all presentations were done by using heavy-ion beams. Although new experimental systems have been introduced, the biological outputs examined were cell death, chromosome aberrations and mutation. We presented the data, for the first time, which indicates bystander effects on cellular differentiation. We used neural stem cells and showed that targeted cells affected neurogenic differentiation of non-targeted neural stem cells.

The next workshop will be held in New York in 2012 by Prof. David Brenner from Columbia University. It is presumed that more studies used 3D-cultured cells and more studies examined bystander effects on differentiation. Stem cells must be the future target for studying non-targeted effects. Such studies are expected to advance our knowledge on the effects induced especially by low dose radiation.
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