The molecular mechanisms of nanotube formation and whether the process of nanotunneling-mediated fusion is the same as conventional mitochondrial fusion involved in both inner and outer mitochondrial membrane fusion merit further investigations. Furthermore, it should be noted that this technique has limitations in the detection of nanotubules. The diameter of nanotubules is reported to be 90 – 210 nm in adult cardiomyocytes, so the resolution of confocal microscopy may not be sensitive enough to catch all the nanotunneling events, if it is also in this case in skeletal muscle. In addition, we also found that mitochondrial network exists in skeletal muscle, evidenced by the KRX-0401 dynamic mtPAGFP study as well as static three-dimensional ultrastructure from EM picture. Photoactivated regions were usually larger than the expected areas of illumination, demonstrating that these mitochondria were physically connected networks. These mitochondrial networks may be important for the contraction or functions of skeletal muscle. Because materials within one network could be transferred rapidly, it has been considered to be an effective way to transmit energy, oxygen and substrates from periphery to the core of muscle cells. Often, skeletal muscle fibers are large and range from 5 to 100 mm in diameter and from 1 or 2 mm up to even several centimeters in length. And these cells need huge energy supply when they contract, so gradients of oxygen and substrates exist from the periphery to the core of the cell, which may limit work performance of cell contraction. Thus, the rapid transport of oxygen, substrates and H+ from the edge to the central through mitochondrial network can well solve this problem. More importantly, we found that mitochondrial dynamics is impaired in HFD-induced mice, which may provide us new insight to study the mechanism of obesity and diabetes. Skeletal muscle is the largest organ in the human body accounting for about 40% of the body weight, and recent studies have identified the central role of skeletal muscle in inducing whole-body insulin resistance and metabolic syndrome. Now the detailed mechanisms and causal relationship between mitochondrial dysfunction and insulin resistance in obesity and diabetes are not clear. Although the roles of mitochondrial shaping proteins in obesity and diabetes are somehow controversial, more and more evidences show that mitochondrial dynamics acts as a hub to bridge mitochondrial dysfunction and insulin resistance. The expression of MFN1, MFN2 and Drp1 was found not to be altered in obese subjects when compared with age-matched lean women by Holloway GP. A series findings by Zorzano’s group also showed that altered expression of OPA1 and decreased expression of MFN2 participated in the development of obesity and type 2 diabetes in both patients and rodent models, which highlighted the importance of MFN2 in metabolism.