What is Cytokinesis?
The cytoplasmic division of a cell at the end of mitosis or meiosis, bringing about the separation into two daughter cells. It is the final step of cell division during which the two daughter cells become physically separated. It begins just after chromosome segregation in anaphase and continues through telophase.
Step 1: Positioning and formation of contractile ring
The first event in animal cell cytokinesis is the formation
of a contractile ring.
What is a contractile ring?
It is a ring-shaped structure made up of actin, myosin
filaments and many structural and regulatory proteins. that
constricts to form cleavage furrow. The positioning of contractile ring at the
center is determined by the central spindle microtubules and astral microtubules.
Step 2: Cleavage furrow ingression by actomyosin
contractile ring
The contraction of these actomyosin filaments is one
of the major driving forces that triggers furrow ingression or pinching of the
plasma membrane inward, and forming a cleavage furrow. Many other proteins like
Rho A proteins are also involved in this process. Rho A activates
Rho-associated kinase (ROCK), which phosphorylates the myosin regulatory light
chain (MRLC), thereby promoting myosin contractility. Actomyosin filaments disappear soon after completion
of furrow ingression.
Step 3: Formation of midbody
The midbody is a temporary structure that
connects two daughter cells at the end of cytokinesis. It consists of tightly
bundled antiparallel microtubules. The function of mid body is to localize the
site of abscission, which physically separates two daughter cells. When
furrow ingression is complete, the midbody appears like a “dark region” with
dense cluster of microtubules.
Step 4: Abscission forming two daughter cells
Cell
division ends with the cutting of the microtubule and membrane intercellular
bridge connecting the 2 daughter cells at specific locations called
constriction sites. This process is known as cytokinetic abscission
(abscission). Endosomal sorting
complex required for transport (ESCRT III), a protein complex mediates the
process of midbody abscission finally forming two daughter cells.
Reference
D'Avino PP, Giansanti MG, Petronczki M.
Cytokinesis in animal cells. Cold Spring Harb Perspect Biol. 2015
Mattissek C, Teis D. The role of the endosomal
sorting complexes required for transport (ESCRT) in tumorigenesis. Mol Membr
Biol. 2014