But the nuclear membrane is regulating what material should be in the nucleus in contrast to what material should be in the cytoplasm. Julie A. Segre, Ph. Featured Content. You have authorized LearnCasting of your reading list in Scitable. Do you want to LearnCast this session? This article has been posted to your Facebook page via Scitable LearnCast. Change LearnCast Settings.
Scitable Chat. The nuclear membrane is a lipid bilayer enclosing the nucleus and physically isolating it from the rest of the cell, which enables important molecular processes to occur in the nucleus, without interference from the cytoplasm. Example images of proteins localized to the nuclear membrane can be seen in Figure 1. A Gene Ontology GO -based functional enrichment analysis of the nuclear membrane proteins shows enrichment of terms for biological processes mainly related to structural organization of the nucleus and nucleocytoplasmic transport.
The most common additional localization except for the nucleoplasm is vesicles. Figure 1. Examples of proteins localized to the nuclear membrane. TPR is part of the nuclear pore complex required in nuclear trafficking, and is specifically involved in nuclear export of mRNAs detected in A cells. SUN2 is known to be part of the LINC protein complexes that enables connection of the cytoskeleton to the nuclear membrane detected in A cells. Of these 37 show a variation in intensity and 4 a spatial variation.
Figure 2. Each bar is clickable and gives a search result of proteins that belong to the selected category. The nuclear membrane, also known as the nuclear envelope, consists of two lipid bilayers. The outermost membrane is contiguous with the endoplasmic reticulum ER , while the innermost membrane is lined by a fibrillar network consisting of nuclear intermediate filament proteins, known as nuclear lamins. The nuclear lamina provides structural support and acts as an anchoring point for chromatin, thus playing an important role in nuclear organization.
Lamins are classified as A- or B-type, and exhibit different biochemical and functional properties in terms of isoelectric points and behavior during mitosis. During the mitotic phase of cell division, B-type lamins will remain associated to membranes, whereas A-type lamins are solubilized and dispersed Gruenbaum Y et al.
A selection of proteins suitable as markers for the nuclear lamina and the nuclear membrane can be found in Table 1. A list of highly expressed nuclear membrane proteins, including lamins, are summarized in Table 2. Table 1. Selection of proteins suitable as markers for the nuclear membrane. Table 2. Highly expressed single localized nuclear membrane proteins across different cell lines. The space between the inner and the outer membrane is called the perinuclear space.
The membranes are connected to each other at large protein complexes, known as nuclear pore complexes, forming a large number of channels that allows for transport in and out of the nucleus. Each nuclear pore complex consists of proteins that form a characteristic eight-fold ring symmetry Paine PL et al.
When imaging an intersection of the cell, the nuclear membrane is visible as a thin circle along the outer rim of the nucleus, which is consistent between cell lines Figure 3. The membrane is however not perfectly smooth and the membranous cavities can appear as small circles or dots inside the nucleus, not to be confused with nuclear bodies.
Figure 3. Examples of the morphology of nuclear membrane in different cell lines, where the morphology is relatively consistent. Figure 4. The morphology of the nuclear membrane in human induced stem cells can be seen in the Allen Cell Explorer. The nuclear membrane serves as a barrier between the nucleus and the cytoplasm, separating gene regulation and transcription in the nucleus from translation in the cytoplasm CALLAN HG et al. The nuclear pores allow for diffusion of small molecules, but also active transport of larger molecules like RNA and proteins, across the nuclear membrane Paine PL et al.
In that sense, the nuclear membrane creates both a barrier, but also a linkage, between the nucleus and the rest of the cell. The nuclear membrane is a highly dynamic structure, with a composition that is altered throughout the cell cycle.
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