Membrane microextension: a possible mechanism for establishing molecular contact in electrofusion

Intercellular interaction observed by atomic force microscopy

The cultured myoblasts, focusing on the microprocesses related to the intercellular interaction, were observed by taking topological images. For atomic force microscopy (AFM), cells were fixed and either dried as in usual scanning electron microscopy or kept in the buffer. The dried cells were used for observing intercellular interactions related to the fusion. The prefusing myoblasts aligned in a chain were mostly spindle in shape and were characterized by the presence of many microprocesses along the facing edges of adjacent aligned myoblasts. The space between fusing myoblasts and between myotubes and myoblasts were often traversed by filopodia and cellular bridges formed by the connection of microvilli. These results suggest that microprocesses may be involved in the fusion of myoblasts. The best images of the fixed cell in liquid were obtained using the contact mode of AFM. AFM observation is an efficient tool in the study on the interaction between cells, and the fixation, imaging in liquid is a good approach to understand the cellular dynamics.

Time scales of membrane fusion revealed by direct imaging of vesicle fusion with high temporal resolution

Membrane fusion is a vital process of life involved, for example, in cellular secretion via exocytosis, signaling between nerve cells, and virus infection. In both the life sciences and bioengineering, controlled membrane fusion has many possible applications, such as drug delivery, gene transfer, chemical microreactors, or synthesis of nanomaterials. Until now, the fusion dynamics has been elusive because direct observations have been limited to time scales that exceed several milliseconds. Here, the fusion of giant lipid vesicles is induced in a controlled manner and monitored with a temporal resolution of 50 micros. Two different fusion protocols are used that are based on synthetic fusogenic molecules and electroporation. For both protocols, the opening of the fusion necks is very fast, with an average expansion velocity of centimeters per second. This velocity indicates that the initial formation of a single fusion neck can be completed in a few hundred nanoseconds.