page_title: Actomyosin ring
section_title: Variation between kingdoms
hierarchical_section_title: Actomyosin ring / Variation between kingdoms
caption_attribution_description: English: Original Figure legend: "A time series of ratio images of a wild type GFP-myosin-II expressing cell going through cytokinesis. The numbers indicate seconds with 0 defined as the point of nuclear division. Bar, 5 μm." From the numbers and images it follows that with "nuclear division" the onset of Anaphase is meant. The Organism is Dictyostelium discoideum. Cell division is similar for animal cells. Deutsch: Übersetzung der Original-Abbildungslegende: „Zeitserie einer Wildtyp-myosin-II exprimierenden Zelle, die durch die Cytokinese geht. Die Zahlen geben Sekunden an, 0 ist der Zeipunkt der Kernteilung. Maßstab: 5 µm.“ Aus den Zeitangaben und den Bildern erfolgt, dass mit „Kernteilung“ der Beginn der Anaphase gemeint ist. Der Organismus ist Dictyostelium discoideum. Die Zellteilung bei tierischen Zellen ist ähnlich
context_page_description: In molecular biology, an actomyosin contractile ring is a prominent structure during cytokinesis. It forms perpendicular to the axis of the spindle apparatus towards the end of telophase, in which sister chromatids are identically separated at the opposite sides of the spindle forming nuclei. The actomyosin ring follows an orderly sequence of events: identification of the active division site, formation of the ring, constriction of the ring, and disassembly of the ring. It is composed of actin and myosin II bundles, thus the term actomyosin. The actomyosin ring operates in contractile motion, although the mechanism on how or what triggers the constriction is still an evolving topic. Other cytoskeletal proteins are also involved in maintaining stability of the ring. Apart from cytokinesis, in which the ring constricts as the cells divide, actomyosin ring constriction has also been found to activate during wound closure. During this process, actin filaments are degraded, preserving the thickness of the ring. After cytokinesis is complete, one of the two daughter cells inherits a remnant known as the midbody ring.
context_section_description: In animals, the ring forms along the cleavage furrow on the inside of the plasma membrane then splits by abscission. In fungi, it forms at the mother-bud neck before mitosis. Septin is heavily involved in the formation of the fungal AMR. In most bacteria and many archaea a homologous structure called the z-ring forms out of FtsZ, a homolog of tubulin. Chloroplasts form an analogous structure out of FtsZ. These structures are not made out of actomyosin, but serve a similar role in constricting and permitting cytokinesis. In plant cells, there is no actomyosin ring. Instead, a cell plate grows centrifugally outwards from the center of the plane of division until it fuses with the existing cell wall.
caption: Fig. 2. The actomyosin ring induces  formation of the cleavage furrow (4th from top) to assist cell cleavage.
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