L10: cytokenesis part 2 Flashcards
filaments?
17nm Filaments at the Site of Abscission: At the site of constriction, 17nm filaments are found. These filaments are believed to be formed by the ESCRT-III complex. They are present at the narrowest points just before abscission, as the two tubular cells prepare to separate from each other.
Helical Structure of Filaments: These filaments form a helical structure at the site of constriction. ESCRT-III is known to make spirals in vitro.
Membrane Remodeling Complex (ESCRT-III): The filaments at the abscission site are most likely pulled by the membrane remodeling complex known as ESCRT-III. ESCRT-III is an ancient membrane remodeling complex that is found at any type of membrane scission.
Assembly of ESCRT-III: The ESCRT-III complex assembles inside the membrane to facilitate membrane remodeling during abscission.
chatgpt: the ESCRT III forms spirals around the intercellular bridge and constrict it?
ESCRT-III?
ESCRT-III Complex and Filaments: These filaments are thought to be formed by the ESCRT-III complex, and Cep55 in mice plays a role in this process.
Neural Progenitors and Sensitivity to ESCRT-III: In the context of normal cells, neural progenitors are the only cell type highly sensitive to ESCRT-III. It seems that ESCRT-III is especially important in these cells compared to others.
Role of ESCRT-III in Tumor Cells vs Normal Cells: ESCRT-III is essential for abscission in cultured tumor cells, but its role in normal cells remains uncertain. It may be crucial for tumor cell abscission, but normal cells might not rely on it in the same way.
Uncertainty about Abscission Mechanism: While ESCRT-III is required for abscission in cultured tumor cells, it is not fully understood how abscission works, especially in normal cells.
ESCRT-III and Abscission in Normal Cells: Interestingly, it turns out that ESCRT-III is dispensable in most normal cells in the organism, suggesting that other mechanisms may be at play in these cells.
ESCRT + Midbody?
ATP Hydrolysis and ESCRT-III Activity: The hydrolysis of ATP to ADP and Pi provides the energy required for the ESCRT-III complex to undergo conformational changes. These changes are necessary for the complex to assemble and remodel the membrane during the final steps of cytokinesis (abscission).
Key Components in ESCRT-III Complex:
VPS4 AAA-ATPase is responsible for disassembling the ESCRT-III complex after it has completed its role in membrane scission, allowing for abscission to occur.
VPS20, SNF7, VPS24, VPS2 are all core components that facilitate the formation of the ESCRT-III spiral structure, which helps pull the membrane apart at the point of abscission.
Now, regarding your image of CEP55 and midbody, the CEP55 protein is crucial in recruiting the ESCRT-III complex to the midbody (the region between the two daughter cells). It helps in the final stages of membrane fission during cytokinesis. This is why your image showing CEP55 and midbody is relevant — it likely illustrates the region where the ESCRT-III complex is acting to facilitate membrane constriction and eventual abscission.
Midbody Constriction and Membrane Bulges: The midbody is where the two daughter cells are connected via interpolar microtubules. The ESCRT-III complex helps in constricting the membrane at this point. The membrane bulges you mentioned could be a result of the mechanical tension at the midbody, where the ESCRT-III complex facilitates the scission by pulling the membrane inward and narrowing it until the cells separate.
Contraction During Outgrowth: The midbody and the constriction occurring here could also relate to the outgrowth of new cell membrane, where the ESCRT-III complex ensures the membrane stays intact and properly segmented during abscission.
In summary, the ATP hydrolysis and the key ESCRT-III components are involved in the membrane remodeling and scission that occurs during cytokinesis, helping to ensure the two daughter cells separate properly. The image with CEP55 and the midbody illustrates this critical region where these processes are occurring, showing how membrane constriction and scission are facilitated by ESCRT-III.
cytokenesis failiure and cancer?
Cytokinesis Failure and Cancer:
Failure to divide the cytoplasm after the nucleus divides results in a binucleated cell.
When the cell enters the next mitosis, both nuclei disassemble, and chromosomes are present in the cytoplasm.
This leads to two spindles forming in the same cytoplasm, which can interact with each other.
Multipolar spindles can form due to the interaction of microtubules from the two spindles.
Multipolar mitosis can result in mitotic failure and DNA damage, contributing to cancer development.
Aurora B Inhibition and Cancer:
In cancer, Aurora B is often inhibited.
This inhibition can result in binucleated cells because it prevents the proper separation of the chromosomes during mitosis.
Inhibition of actomyosin also plays a role, as it disrupts the contractile ring formation, leading to defective cytokinesis.
Anaphase bridges may form, which are structures that bridge the gap between chromosomes, preventing proper separation and leading to chromosome missegregation and further genomic instability.
cytokenesis and cell fate?
Importance of Cytokinesis in Cell Fate:
Proper placement of the division furrow is critical for cell fate specification and development.
Cytokinesis does not always occur in the middle of the cell.
In C. elegans, the small cell inherits certain granules that eventually signal the formation of germ cells for reproduction.
This process does not necessarily happen in the center of the cell.
correct orientation of cytokenesis?
Correct Orientation of Cytokinesis and Cell Fate Specification:
Correct orientation of cytokinesis is critical for cell fate specification and development.
In the development of the brain, proper cytokinesis ensures the formation of a normal brain versus a microcephalic brain.
Epithelial cells must undergo several symmetrical divisions. Only when a sufficient number of neural epithelial cells are generated can they undergo asymmetrical division to produce neurons.
If cells do not undergo both symmetrical and asymmetrical divisions, neurons cannot be generated.
Cytokinesis Mechanisms in Different Organisms:
Budding in Yeast:
Yeast first specifies the division site and then grows and divides asymmetrically.
Plant Cells:
Plant cells divide in a unique manner: not centripetally, but from inside out.
Phragmoplast formation: Plant cells assemble a phragmoplast that grows outward during division.
Pregophase: A band of microtubules and actin filaments forms in the plant cells.
Remains of the interpolar spindle microtubules and a cortical array of interphase microtubules contribute to this process.
plant cell cytokenesis?
- Preprophase Band
A ring of microtubules and actin filaments forms just beneath the plasma membrane before mitosis begins.
This band marks the future site of cell division (where the new cell wall will form).
It disappears early in mitosis, but the division site remains “remembered” by the cell.
- Phragmoplast Formation
After chromosomes separate during mitosis, plant cells form a structure called the phragmoplast.
The phragmoplast is made from remnants of the interpolar microtubules left over from the mitotic spindle.
It forms between the two daughter nuclei and guides the assembly of the new cell wall (called the cell plate).
- Cell Plate Formation
Vesicles from the Golgi apparatus move along the phragmoplast microtubules and fuse at the center of the cell.
These vesicles contain materials to build the new cell wall.
The cell plate grows outward toward the edges of the cell until it connects with the original cell wall, dividing the cell in two.
- Cortical Microtubule Array
After division, the cell reorganizes its microtubules into a cortical array.
These interphase microtubules help with cell wall orientation and future cell shape.
common/critical factors for cytokenesis
common/ Critical Factors for Cytokinesis:
Timing:
Cytokinesis must occur only after chromosomes are segregated.
If cytokinesis is not timed properly and the division site is assembled before segregation, there is a risk of cutting chromosomes and causing DNA damage.
Placement:
Cytokinesis must occur between the segregated chromosomes.
The plane of division often determines the cell fates of the daughter cells.
Incorrect placement could result in one daughter cell with a nucleus, and the other without, or even cutting the nucleus in two.
Plasticity:
Cytokinesis mechanisms exhibit bewildering diversity across eukaryotes.
