The nuclear envelope and nuclear pore complex as seen by high-resolution field emission SEM and high voltage TEM

Abstract

The nuclear envelope (NE) consists of an inner membrane and an outer membrane continuous with the endoplasmic reticulum. The membranes are fused at the nuclear pores, which connect cytoplasm with nuclear space. Located in these pores is the nuclear pore complex (NPC) which controls the transport of macromolecules across the NE. Attached to the inner surface of the NE is a network of 10 nm lamin filaments, the nuclear lamina. Recent studies using high voltage TEM and field emission “in lens” SEM have greatly advanced our knowledge of NPC structure, particularly the components facing the cytoplasm and nuclear space. The cytoplasmic face consists of a 120 nm ring carrying 8 twisted filaments condensed into 20×40 nm cylinders. On the nuclear side is another 120 nm ring, from which 8 filaments, 5 nm thick and 50 nm long, extend into the nuclear space. Each filament ends in a 10 nm bead. The 8 beads are joined into a 50 nm ring, forming the top of a fishtrap-like structure. Usually this ring is obscured by distorted pore connecting fibers.