Draft:Original research/Cytokinesis

Cytokinesis is a name applied to the cell separation phase of the cell division process.

Biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes within, and relating to, living organisms.

Mitosis
Mitosis is the process by which nucleated cells duplicate.

Mitosis is one of the phases of the cell cycle.

Def. the "division of a cell nucleus in which the genome is copied and separated into two identical halves" is called mitosis.

After S phase, there is another interphase, known as Gap 2, or G2. Then mitosis starts off the M phase. In M phase, the two copies of DNA are separated from each other and one copy each is given to each “daughter”. The daughters are actually the cell itself divided into two halves, each half having what a whole cell needs. During mitosis, the DNA becomes visible within the nucleus of the cell (its home) because the chromosomes are duplicates folded up tightly. They are lined up across the middle of the nucleus and the copies are pulled apart to opposite poles of the cell.

After this has occurred, cytokinesis can ensue. In this process, the cell itself divides, and each “pole” becomes a new nucleus in the new cells.

Theoretical cytokinesis
Def. a cytoplasmic division of a cell at the end of mitosis or meiosis bringing about the separation into daughter cells is called cytokinesis.

Def. the "process in which the cytoplasm of a cell divides following the division of the nucleus" is called cytokinesis.

Def. a "movement of an organism in response to an external stimulus" is called kinesis.

Def. forming "words regarding or pertaining to cells" is called cyto-.

In its perhaps simplest sense,

Def. a movement of a cell by that cell is called cytokinesis, or

Def. a self-propelled movement of a cell is called cytokinesis.

Animal cytokinesis
Animal cell cytokinesis which begins shortly after the onset of sister chromatid separation in the anaphase of mitosis can be divided to the following distinct steps: anaphase spindle reorganization, division plane specification, actin-myosin ring assembly and contraction, and abscission.

The process of mitotic spindle reorganization and central spindle formation is caused by the decline of CDK1 activity during anaphase.

The central spindle may have multiple functions in cytokinesis including the control of cleavage furrow positioning, the delivery of membrane vesicles to the cleavage furrow, and the formation of the midbody structure that is required for the final steps of division.

Rho protein family (RhoA protein in mammalian cells) is a key regulator of contractile ring formation and contraction in animal cells. The RhoA pathway promotes assembly of the actin-myosin ring by two main effectors. First, RhoA stimulates nucleation of unbranched actin filaments by activation of Diaphanous-related formins. This local generation of new actin filaments is important for the contractile ring formation.

The cytokinetic furrow ingresses until a so-called 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 bridge for up to several hours until they are split by an actin-independent process termed abscission, the last step of 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.

Ras homolog family members
Notation: let Rho stand for Ras homolog family members.

"Rho regulates cytokinesis".

Gene ID: 387 RHOA ras homolog family member A
"This gene encodes a member of the Rho family of small GTPases, which cycle between inactive GDP-bound and active GTP-bound states and function as molecular switches in signal transduction cascades. Rho proteins promote reorganization of the actin cytoskeleton and regulate cell shape, attachment, and motility. Overexpression of this gene is associated with tumor cell proliferation and metastasis. Multiple alternatively spliced variants have been identified."

Gene ID: 389 RHOC ras homolog family member C
"This gene encodes a member of the Rho family of small GTPases, which cycle between inactive GDP-bound and active GTP-bound states and function as molecular switches in signal transduction cascades. Rho proteins promote reorganization of the actin cytoskeleton and regulate cell shape, attachment, and motility. The protein encoded by this gene is prenylated at its C-terminus, and localizes to the cytoplasm and plasma membrane. It is thought to be important in cell locomotion. Overexpression of this gene is associated with tumor cell proliferation and metastasis. Multiple alternatively spliced variants, encoding the same protein, have been identified."

Gene ID: 29984 RHOD ras homolog family member D
"Ras homolog, or Rho, proteins interact with protein kinases and may serve as targets for activated GTPase. They play a critical role in muscle differentiation. The protein encoded by this gene binds GTP and is a member of the small GTPase superfamily. It is involved in endosome dynamics and reorganization of the actin cytoskeleton, and it may coordinate membrane transport with the function of the cytoskeleton. Two transcript variants encoding different isoforms have been found for this gene."

Hypotheses

 * 1) Cytokinesis uses all types of triphosphates.
 * 2) The genes that control cytokinesis also control melanoblast migration.