Sample preparation for electron microscopy of internal cell structure.

Methods are reviewed for examination of internal cell structure by high-resolution scanning electron microscopy and compared with the rapid-freeze deep-etch replica technique used in transmission electron microscopy. Rapid freezing of fresh material, followed by freeze-fracture, provides a theoretically attractive approach in ultrastructure studies, but the high protein and solute content of most cells prevents a deep three-dimensional view for material frozen without some form of extraction. After discussion of other methods it is concluded that the most useful general approach, at least for cultured cells, is to first permeabilize or break open the cells in a medium which preserves the structure under study in a functional state as, for example, the movement of chromosomes along the division spindle, or transport of proteins within the Golgi region. After permeabilization, with attendant partial extraction, the preparation can be fixed, then viewed by either deep-etch replication, or by high-resolution scanning electron microscopy, with structure of interest revealed in deep view.