Thecell cortex, also known as theactin cortex, cortical cytoskeleton oractomyosin cortex, is a specialized layer ofcytoplasmicproteins on the inner face of thecell membrane. It functions as a modulator of membrane behavior and cell surface properties.^[1][2][3] In mosteukaryotic cells lacking acell wall, the cortex is anactin-rich network consisting ofF-actin filaments,myosin motors, and actin-binding proteins.^[4][5] The actomyosin cortex is attached to thecell membrane via membrane-anchoring proteins calledERM proteins that plays a central role in cell shape control.^[1][6] The protein constituents of the cortex undergo rapid turnover, making the cortex both mechanically rigid and highly plastic, two properties essential to its function. In most cases, the cortex is in the range of 100 to 1000nanometers thick.

In some animal cells, the proteinspectrin may be present in the cortex. Spectrin helps to create a network by cross-linked actin filaments.^[3] The proportions of spectrin and actin vary with cell type.^[7] Spectrin proteins and actin microfilaments are attached to transmembrane proteins by attachment proteins between them and the transmembrane proteins. The cell cortex is attached to the innercytosolic face of theplasma membrane in cells where the spectrin proteins and actin microfilaments form a mesh-like structure that is continuously remodeled bypolymerization,depolymerization and branching.

Many proteins are involved in the cortex regulation and dynamics, includingformins, with roles in actin polymerization,Arp2/3 complexes that give rise to actin branching andcapping proteins. Due to the branching process and the density of the actin cortex, the corticalcytoskeleton can comprise a highly complex meshwork such as afractal structure.^[8] Specialized cells are usually characterized by a very specific cortical actin cytoskeleton. For example, inred blood cells, the cell cortex consists of a two-dimensional cross-linked elastic network with pentagonal or hexagonal symmetry, tethered to the plasma membrane and formed primarily byspectrin, actin andankyrin.^[9] In neuronalaxons, the actin or spectric cytoskeleton forms an array of periodic rings^[10] and in thespermflagellum it forms ahelical structure.^[11]

Inplant cells, the cell cortex is reinforced by corticalmicrotubules underlying the plasma membrane. The direction of these cortical microtubules determines which way the cell elongates when it grows.

The cortex mainly functions to produce tension under the cell membrane, allowing the cell to change shape.^[12] This is primarily accomplished throughmyosin II motors, which pull on the filaments to generate stress.^[12] These changes in tension are required for the cell to change its shape as it undergoescell migration andcell division.^[12]

Inmitosis,F-actin and myosin II form a highly contractile and uniform cortex to drivemitotic cell rounding. The surface tension produced by the actomyosin cortex activity generates intracellularhydrostatic pressure capable of displacing surrounding objects to facilitate rounding.^[13][14]Thus, the cell cortex serves to protect the microtubule spindle from external mechanical disruption during mitosis.^[15] When external forces are applied at sufficiently large rate and magnitude to a mitotic cell, loss of cortical F-actin homogeneity occurs leading to herniation of blebs and a temporary loss of the ability to protect the mitotic spindle.^[16][17] Genetic studies have shown that the cell cortex in mitosis is regulated by diverse genes such as Rhoa,^[18] WDR1,^[19] ERM proteins,^[20] Ect2,^[21] Pbl, Cdc42, aPKC, Par6,^[22] DJ-1 and FAM134A.^[23]

Incytokinesis the cell cortex plays a central role by producing a myosin-rich contractile ring to constrict the dividing cell into two daughter cells.^[24]

Cell cortex contractility is key foramoeboidal type cell migration characteristic of many cancer cellmetastasis events.^[1][25]

In addition to cell cortex also plays essential roles in the formation of tissues, organs and organisms. By pulling on adhesion complexes, the cortex promotes the expansion of contacts with other cells or with theextracellular matrix. Notably, during early mammalian development, the cortex pulls cells together to drive compaction and the formation of themorula.^[26][27] Also, differences in cortical tension drives the sorting of theinner cell mass andtrophectoderm progenitors during the formation of themorula,^[28] the sorting ofgerm layer progenitors duringzebrafishgastrulation,^[29][30] the invagination of themesoderm and the elongation of thegerm band elongation during drosophila gastrulation.^[31][32]

Basic research into the cell cortex is done withimmortalised cell lines, typicallyHeLa cells,S2 cells,Normal rat kidney cells, andM2 cells.^[12] In M2 cells in particular,cellular blebs – which form without a cortex, then form one as they retract – are often used to model cortex formation and composition.^[12]

• Bray, Dennis (2000). "Actin and Membranes".Cell Movements. pp. 81–101.doi:10.4324/9780203833582-7.ISBN 978-0-203-83358-2.

• Cytoskeleton
• Cell biology

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