Nuclear envelope

The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes that in eukaryotic cells surround the nucleus, which encloses the genetic material. The nuclear envelope consists of two lipid bilayer membranes: an inner nuclear membrane and an outer nuclear membrane. The space between the membranes is called the perinuclear space. It is usually about 10–50 nm wide. The outer nuclear membrane is continuous with the endoplasmic reticulum membrane. The nuclear envelope has many nuclear pores that allow materials to move between the cytosol and the nucleus. Intermediate filament proteins called lamins form a structure called the nuclear lamina on the inner aspect of the inner nuclear membrane and give structural support to the nucleus. The nuclear envelope is made up of two lipid bilayer membranes, an inner nuclear membrane and an outer nuclear membrane. These membranes are connected to each other by nuclear pores. Two sets of intermediate filaments provide support for the nuclear envelope. An internal network forms the nuclear lamina on the inner nuclear membrane. A looser network forms outside to give external support. The actual shape of the nuclear envelope is irregular. It has invaginations and protrusions and can be observed with an electron microscope. The outer nuclear membrane also shares a common border with the endoplasmic reticulum. While it is physically linked, the outer nuclear membrane contains proteins found in far higher concentrations than the endoplasmic reticulum. All four nesprin proteins (nuclear envelope spectrin repeat proteins) present in mammals are expressed in the outer nuclear membrane. Nesprin proteins connect cytoskeletal filaments to the nucleoskeleton. Nesprin-mediated connections to the cytoskeleton contribute to nuclear positioning and to the cell’s mechanosensory function. KASH domain proteins of Nesprin-1 and -2 are part of a LINC complex (linker of nucleoskeleton and cytoskeleton) and can bind directly to cystoskeletal components, such as actin filaments, or can bind to proteins in the perinuclear space.