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Nuclear Envelope The nuclear envelope refers to the double membrane of the nucleus that encloses genetic material in eukaryotic cells. It separates the contents of the nucleus (DNA in particular) from the cytosol. The space between the two membranes that make up the nuclear envelope is called the perinuclear space, and is usually about 20 - 100 nm wide. The outer membrane is continuous with the rough endoplasmic reticulum. Numerous nuclear pores are present on the nuclear envelope to facilitate and regulate the exchange of materials (for example, proteins and mRNA) between the nucleus and the cytoplasm. The inner membrane is erected upon the nuclear lamina, a network of intermediate filaments made of lamin. This network of filaments is essential for the disarrangement of the nuclear envelope into vesicles during mitosis or meiosis, and its posterior reassembly. When, during the cell cycle, a certain cyclin-dependent kinase complex phosphorylates the lamins they undergo a conformational change that triggers the disassembly of the nuclear envelope. After the chromosomes have migrated to each pole, dephosphorylation of lamins causes the nucleus to reassemble. The nuclear envelope may also play a role in the disposition of chromatin inside the nucleus. Synonyms: karyotheca, nuclear membrane, nucleolemma, perinuclear envelope
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