Metaphase defined by alignment of condensed chromosomes along equatorial plate equidistant between spindle poles is visually hallmark of mitosis used for karyotyping. Following prometaphase, chromosomes undergo congression driven by opposing forces: CENP-E plus-end-directed kinesin transporting chromosomes toward plate, and dynein mediated poleward force, plus dynamic instability of microtubules causing oscillations. Correct amphitelic attachment where sister kinetochores bind microtubule bundles emanating from opposite centrosomes generates tension across centromere stretching inter-kinetochore distance, satisfying checkpoint. Erroneous syntelic or merotelic attachments lacking tension are destabilized by Aurora B kinase concentrated at inner centromere phosphorylating Ndc80 and KNL1 reducing microtubule affinity, giving second chance for proper biorientation. When all chromosomes aligned, metaphase plate forms, cyclin B-CDK1 activity remains maximal maintaining condensin activity and securin stability, and spindle assembly checkpoint silences awaiting anaphase trigger, ensuring synchronous segregation for equal genome distribution. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.
Ref:
Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17, Metaphase Alignment Mechanisms.
