Three-dimensional ultrastructure of osteocytes assessed by focused ion beam-scanning electron microscopy (FIB-SEM)
The aim of this study is to demonstrate the application of focused ion beam-scanning electron microscopy, FIB-SEM for revealing the three-dimensional features of osteocytic cytoplasmic processes in metaphyseal (immature) and diaphyseal (mature) trabeculae. Tibiae of eight-week-old male mice were fixed with aldehyde solution, and treated with block staining prior to FIB-SEM observation. While two-dimensional backscattered SEM images showed osteocytes’ cytoplasmic processes in a fragmented fashion, three-dimensional reconstructions of FIB-SEM images demonstrated that osteocytes in primary metaphyseal trabeculae extended their cytoplasmic processes randomly, thus maintaining contact with neighboring osteocytes and osteoblasts. In contrast, diaphyseal osteocytes extended thin cytoplasmic processes from their cell bodies, which ran perpendicular to the bone surface. In addition, these osteocytes featured thick processes that branched into thinner, transverse cytoplasmic processes; at some point, however, these transverse processes bend at a right angle to run perpendicular to the bone surface. Osteoblasts also possessed thicker cytoplasmic processes that branched off as thinner processes, which then connected with cytoplasmic processes of neighboring osteocytes. Thus, FIB-SEM is a useful technology for visualizing the three-dimensional structures of osteocytes and their cytoplasmic processes.
KeywordsFIB-SEM Osteocyte Osteoblast Three-dimensional structure Bone
This study was partially supported by the Grants-in Aid for Scientific Research of JSPS (Hasegawa T and Amizuka N) and the Nanotechnology Platform Program of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan (Hasegawa T).
Compliance with ethical standards
The animal protocols used in this study were approved by the Hokkaido University Guidelines for Animal Experimentation (approval No. 15-0041).
Conflict of interest
No potential conflicts of interest exist.
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