CorpusHuman Anatomy
Cells & TissuesOrganelle

Nuclear envelope and nuclear pores

Involucrum nucleare

Also known as: nuclear membrane, nuclear pore complex, NPC, perinuclear space, nuclear lamina, lamins

Two concentric lipid bilayers around the nucleus, separated by the perinuclear space and fused at thousands of nuclear pore complexes that control traffic between nucleus and cytoplasm.

The Eukaryotic Cell

Overview

Nuclear pores per nucleus≈2000–4000 (mammalian)
NPC mass≈110–120 MDa; ≈30 nucleoporin types
Free-diffusion limit≈40 kDa

The outer nuclear membrane is continuous with the rough ER and is studded with ribosomes; the perinuclear space (≈20–50 nm) between the two membranes is continuous with the ER lumen. The inner nuclear membrane contains specific proteins (lamin B receptor, emerin, SUN proteins) that bind the nuclear lamina and chromatin. LINC complexes (SUN–nesprin) span the envelope and link the lamina to the cytoskeleton, transmitting mechanical forces to the nucleus.

Nuclear pore complexes (NPCs) are huge (≈110–120 MDa in vertebrates, ≈100–120 nm across) assemblies of ≈30 different nucleoporins arranged with eightfold symmetry, present at about 2000–4000 per mammalian nucleus. Their central channel is filled with disordered FG-repeat nucleoporins that form a selective barrier: ions, metabolites and small proteins (up to ≈40 kDa) diffuse through, whereas larger molecules require active, signal-mediated transport. Proteins with a nuclear localisation signal (short basic sequences, e.g. PKKKRKV) are carried in by importins; molecules with a nuclear export signal are carried out by exportins. Direction is set by the Ran GTPase gradient — Ran-GTP is high in the nucleus (its GEF, RCC1, is bound to chromatin) and low in the cytosol (Ran-GAP). Processed mRNAs leave as mRNA–protein complexes via a separate export receptor (NXF1/TAP).

At the start of mitosis CDK1 phosphorylates lamins and nucleoporins, causing the envelope to disassemble (prometaphase); it re-forms around the separated chromosomes in telophase after dephosphorylation.

Parts & subdivisions

  1. Outer nuclear membrane
    Continuous with RER; carries ribosomes.
  2. Perinuclear space (cisterna)
    ≈20–50 nm lumen continuous with the ER lumen.
  3. Inner nuclear membrane
    Bound to lamina and chromatin.
  4. Nuclear pore complex
    Gated channel for nucleocytoplasmic transport.
  5. Nuclear lamina
    Lamin A/C and B meshwork; mechanical support, chromatin anchorage, envelope reassembly.

Anatomy

Histology

By light microscopy the envelope appears as the sharp outline of the nucleus. EM shows the double membrane interrupted by pores, with heterochromatin lining the inner membrane except at the pores (channels for traffic).

Function

  • Separates transcription and RNA processing from translation.
  • Regulates import of proteins (histones, polymerases, transcription factors) and export of RNAs and ribosomal subunits.
  • Organises chromatin at the nuclear periphery (heterochromatin anchorage).
  • Mechanical protection and mechanotransduction.

Clinical significance

Laminopathies

LMNA mutations cause Hutchinson–Gilford progeria (a truncated, farnesylated lamin A — "progerin" — gives misshapen nuclei and premature ageing, atherosclerosis and death in the teens), autosomal dominant Emery–Dreifuss muscular dystrophy, dilated cardiomyopathy with conduction defects and familial partial lipodystrophy. X-linked Emery–Dreifuss dystrophy is due to emerin deficiency.

Anti-nucleoporin antibodies

Antibodies against gp210 and p62 nucleoporins (a "nuclear rim" ANA pattern) are highly specific for primary biliary cholangitis.

Compiled from standard anatomy and physiology references — see the Cells & Tissues sources. For education only; not medical advice.