Skip to content
Login Register

#chromosome separation

4 public questions tagged with this topic.

Cell Division

What happens during anaphase II of meiosis?

Meiosis consists of two divisions following single S phase, with meiosis II equationally separating sisters after reductional meiosis I segregated homologs. Cells exit meiosis I entering interkinesis without replication, centrosomes duplicate, chromosomes recondense, and spindle reforms often orthogonal to first division axis. At metaphase II plate, sister chromatids align with kinetochores bioriented to opposite poles similar to mitosis, achieved despite haploid chromosome number. Protection of centromeric cohesion established in meiosis I by Shugoshin SGO2 bound to PP2A phosphatase that deph

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 21: Meiosis II Sister Chromatids.

View Details
Cell Cycle Regulation

Which protein is degraded by APC to trigger chromosome separation?

Chromatid cohesion must be maintained until synchronous separation at anaphase, requiring protection against premature cleavage. Securin, also called pituitary tumor transforming gene PTTG, functions as dual inhibitor and chaperone of separase. Securin sequence contains D-box and KEN motifs for APC/C recognition and binds separase HEAT repeats, occluding catalytic triad. Accumulation during S and G2 concentrates at centromeres. At metaphase, APC/C-Cdc20 polyubiquitinates securin, triggering rapid proteasomal degradation within five to ten minutes, concentration dropping precipitously. Simultan

Ref: Uhlmann et al., Nature 1999, Separase Cohesin Cleavage. Alberts 7th ed., Chapter 17, Securin.

View Details
Cell Cycle Regulation

Separase is activated when:

Separase activation integrates checkpoint satisfaction with physical separation of chromatids. Newly synthesized separase folds with assistance of securin chaperone, which inserts its own reactive site loop into catalytic pocket, blocking proteolysis and ensuring proper localization to nucleus. Parallel inhibition involves CDK1-Cyclin B1 binding phosphorylating separase at Ser1126 creating docking site for cyclin B. At metaphase, with all kinetochores amphitelically attached, spindle assembly checkpoint silencing allows APC/C-Cdc20 E3 ligase to become active. APC/C-Cdc20 recognizes KEN-box and

Ref: Peters, Control of Securin Degradation by APC/C-Cdc20, Nat Rev Mol Cell Biol; Hornig et al., Securin-Separase Complex Structure.

View Details