High-resolution field-emission scanning electron microscopy of nuclear pore complex.

The nuclear pore complex (NPC) is a large macromolecular assembly inserted into the nuclear envelope (NE). It controls the traffic of proteins, RNA, and RNA proteins between nucleus and cytoplasm. It chemical composition and function are now intensively investigated in many organisms. To understand this unique membrane transport system, we must know the supramolecular organization of the NPC. In recent years, high-resolution field-emission scanning electron microscopy has made important contributions to our knowledge of NPC structure. It provided the first images of the complex and beautiful fish trap-like structure of its intranuclear surface, documented in this review. It also has provided the first images of a new intranuclear structure, a system of branching hollow cables connecting the nuclear interior with the NPCs at the nuclear surface. Most likely this is an intranuclear transport system, assuring efficient exchange between the nuclear interior and the NE, especially in large nuclei.