Kernmembran

Kernmembran, or nuclear envelope, is the double membrane that surrounds the nucleus in eukaryotic cells, separating the nucleoplasm from the cytoplasm. It consists of an inner and outer lipid bilayer separated by the perinuclear space. The outer membrane is continuous with the endoplasmic reticulum and often studded with ribosomes, while the inner membrane supports a lattice known as the nuclear lamina.

The envelope hosts nuclear pore complexes, large protein assemblies that span both membranes and regulate traffic between the nucleus and cytoplasm. Transport through these pores is mediated by karyopherins (importins and exportins) and driven by a Ran GTPase gradient, enabling selective import of proteins with nuclear localization signals and export of RNA and ribonucleoprotein particles.

Attached to the inner membrane are lamins and other transmembrane proteins that anchor chromatin and influence gene regulation, nuclear organization, and genome stability. The Kernmembran thus contributes to DNA replication, repair, and transcriptional control, while also providing mechanical support to the nucleus.

During cell division, the nuclear envelope's behavior varies by organism. In open mitosis, the envelope disassembles to allow chromosome segregation and reassembles around daughter genomes afterward. In closed mitosis, the envelope remains intact while chromosomes segregate. Reformation of the envelope occurs during telophase or cytokinesis in many cells.

Clinical relevance exists for defects in nuclear envelope components, notably lamins and associated proteins, which can cause a range of diseases known as laminopathies, including certain muscular dystrophies and metabolic disorders.

Etymology: Kernmembran is German for nuclear membrane; in English, the term is nuclear envelope.