Cytokinesis performs an essential process to separate the cell in half and ensure that one nucleus ends up in each daughter cell. Cytokinesis starts during the nuclear division phase called anaphase and continues through telophase. A ring of protein filaments called the contractile ring forms around the equator of the cell just beneath the plasma membrane. The contractile ring shrinks at the equator of the cell, pinching the plasma membrane inward, and forming what is called a cleavage furrow. Eventually, the contractile ring shrinks to the point that there are two separate cells each bound by its own plasma membrane.
Animal Cell
Animal cell cytokinesis begins shortly after the onset of sister chromatid separation in the anaphase of mitosis. The process can be divided to the following distinct steps: anaphase spindle reorganization, division plane specification, actin-myosin ring assembly and contraction, and abscission. Faithful partitioning of the genome to emerging daughter cells is ensured through the tight temporal coordination of the above individual events by molecular signaling pathways.
Anaphase spindle reorganization
Animal cell cytokinesis starts with the stabilization of microtubules and reorganization of the mitotic spindle to form the central spindle. The central spindle (or spindle midzone) forms when non-kinetochore microtubule fibers are bundled between the spindle poles.
Division plane specification
The control of cell division plane orientation is crucial in biology and most particularly in plants, in which cells cannot rearrange their positions, as they are glued to each other by their cell walls. Cell geometry has long been proposed to determine cell division plane orientation. Here, using statistical analysis, modeling, and live imaging in the Arabidopsis shoot apex, we show that plant cells instead divide along maximal tension.
Actin-myosin ring assembly and contraction
At the cytokinesis furrow, it is the actin-myosin contractile ring that drives the cleavage process, during which cell membrane and wall grow inward, which eventually pinches the mother cell in two. The key components of this ring are the filamentous protein actin and the motor protein myosin II. The contractile ring assembles equatorially (in the middle of the cell) at the cell cortex (adjacent to the cell membrane). Rho protein family (RhoA protein in mammalian cells) is a key regulator of contractile ring formation and contraction in animal cells.
Abscission
The cytokinetic furrow ingresses until a midbody structure (composed of electron-dense, proteinaceous material) is formed, where the actin-myosin ring has reached a diameter of about 1–2 μm. Most animal cell types remain connected by an intercellular cytokinetic bridge for up to several hours until they are split by an actin-independent process termed abscission, the last step of cytokinesis.
Timing cytokinesis
Cytokinesis must be temporally controlled to ensure that it occurs only after sister chromatids separate during the anaphase portion of normal proliferative cell divisions. To achieve this, many components of the cytokinesis machinery are highly regulated to ensure that they are able to perform a particular function at only a particular stage of the cell cycle. Cytokinesis happens only after APC binds with CDC20. This allows for the separation of chromosomes and myosin to work simultaneously.
Plant Cell
Due to the presence of a cell wall, cytokinesis in plant cells is significantly different from that in animal cells, Rather than forming a contractile ring, plant cells construct a cell plate in the middle of the cell. The stages of cell plate formation include (1) creation of the phragmoplast, an array of microtubules that guides and supports the formation of the cell plate; (2) trafficking of vesicles to the division plane and their fusion to generate a tubular-vesicular network; (3) continued fusion of membrane tubules and their transformation into membrane sheets upon the deposition of callose, followed by deposition of cellulose and other cell wall components; (4) recycling of excess membrane and other material from the cell plate; and (5) fusion with the parental cell wall
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