Fig. 3: Appearance of TNTs in culture cells and classification of TNTs by SEM analysis. | Laboratory Investigation

Fig. 3: Appearance of TNTs in culture cells and classification of TNTs by SEM analysis.

From: In vitro and in vivo detection of tunneling nanotubes in normal and pathological osteoclastogenesis involving osteoclast fusion

Fig. 3

SEM observation of TNT-like structures in 2 days (a) and multinucleated osteoclast-like cells (c) in 3 days of cultured RAW-D cells in osteoclastogenesis. b and d are high magnification views of the boxed areas in (a and c), respectively. Arrows show TNT-like structures formed in cultured osteoclast precursors. TNTs were classified into three types based on the diameter, length, morphology, and connected cell characteristics; e Small diameter nanotubes (Thin nanotubes): Thin nanotubes were observed mainly in small early osteoclast precursors. Straight and less branched TNTs were observed (arrow). f Middle diameter nanotubes (Medium nanotubes): Medium nanotubes were present in small or medium sized late osteoclast precursors or small-sized multinucleated osteoclast-like cells, which were observed as one relatively longer and thicker tube (arrows). Fine branches were observed in these TNTs (arrowheads in f). g Large diameter nanotubes (Thick nanotubes): Thick nanotubes were observed between two multinucleated osteoclast-like cells. These TNTs are thick and slightly shorter (arrow). h, i Quantitative demonstration of the three types TNTs observed in osteoclastogenesis: Difference in the diameter (h) and the length (i) of TNTs. Values represent mean ± SEM from at least three independent experiments. *P < 0.05 (n = 50). e-OCP: early osteoclast precursor. l-OCP: late osteoclast precursor. OC: multinucleated osteoclast-like cell. Scale bars: 10 µm (a–g).

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