Nuclear envelope

Human cell nucleus

A nuclear envelope (also known as the nuclear membrane, nucleolemma or karyotheca) is a double lipid bilayer that encloses the genetic material in eukaryotic cells. The nuclear membrane also serves as the physical barrier, separating the contents of the nucleus (DNA in particular) from the cytoplasm. Many nuclear pores are inserted in the nuclear envelope, which facilitate and regulate the exchange of materials (proteins such as transcription factors, and RNA) between the nucleus and the cytoplasm.

Each of the two membranes is composed of a lipid bilayer. The outer membrane is continuous with the rough endoplasmic reticulum while the inner nuclear membrane is the primary residence of several inner nuclear membrane proteins. The outer and inner nuclear membrane are fused at the site of nuclear pore complexes. The structure of the membrane also consists of ribosomes.

File:The three layers of the nuclear membrane proteins.jpg

The three layers of the nuclear membrane proteins. The nuclear pore complex (NPC) transverses the inner and outer nuclear membranes. Perinuclear space is clearly visible. INM proteins, including SUN1, LAP2, Emerin, MAN1 and LBR, are mostly associated with the nuclear lamina. Emerin, LAP2 and MAN1 harbor a LEM domain which interacts with BAF (barrier-to-autointegration factor), a chromatin-binding protein. The nuclear lamina forms a meshwork underlying the inner nuclear membrane. Chi et al. Journal of Biomedical Science 2009.

The inner nuclear membrane is connected to the nuclear lamina, a network of intermediate filaments composed of various lamins (A, B1, B2, & C). The lamina acts as a site of attachment for chromosomes and provides structural stability to the nucleus. The lamins have been associated with various genetic disorders collectively termed laminopathies.

The space between the two membranes that make up the nuclear membrane itself is called the perinuclear space (also called the perinuclear cisterna, NE Lumen), and is usually about 20 - 40 nm wide.

The nuclear membrane has been postulated to play a role in the organization and transcriptional activity of chromatin. The envelope's form is changing in cell reproduction, and is reforming after the division to daughter cells is completed.

External links

• Histology image: 20102loa – Histology Learning System at Boston University
• Animations of nuclear pores and transport through the nuclear envelope
• Illustrations of nuclear pores and transport through the nuclear membrane
• Nuclear+membrane at the U.S. National Library of Medicine Medical Subject Headings (MeSH)