[Intravital multiphoton imaging of live bone tissues revealing hematopoietic cell dynamics in vivo]

During the last decade, multiphoton fluorescent microscopy has launched a new era in the field of biology. By using this advanced imaging technique we have established a system for visualizing the in situ behaviors of a diversity of living cells within intact tissues and organs. Among them we succeeded in visualizing the various dynamic phenomena within bones, a mysterious organ wherein various hematopoietic and immune cells are produced and functioning. However, these cell types are poorly understood with conventional methodologies such as histological analyses of decalcified bone sections. We have thus far focused on the behavior of osteoclasts, a type of specialized macrophage contributing to physiological turnover of bone tissues as well as pathological bone destruction, and have revealed novel mechanisms controlling the migration and function of osteoclasts in situ. Functional coupling between bone-destroying osteoclasts and bone-replenishing osteoblasts could also be visualized demonstrating a genuine mode of 'cross-talk' among these cell types. Furthermore, we have recently imaged in situ behaviors of different hematopoietic cells in bone marrow. Herein we present our latest data on cellular dynamics in the bone cavity, and discuss the applications of this novel methodology for future studies in the field of hematology.