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#chromosome alignment

9 public questions tagged with this topic.

Cytoskeleton

During mitosis, kinetochore microtubules:

Kinetochore microtubule fibers K fibers dynamic behavior changes across mitotic stages governed by tension sensing checkpoint signaling and motor forces generating chromosome movement. During prometaphase microtubules nucleated at centrosomal poles probe cytoplasm via dynamic instability growth at plus end at several microns per minute capture kinetochore through NDC80 complex forming bundles of 20 to 40 microtubules stabilized by CLASP and formins. Until anaphase kinetochore microtubules continue polymerization at plus end while minus ends depolymerize at poleward flux mediated by kinesin-13

Ref: Cheeseman & Desai, Annu Rev Cell Dev Biol – Kinetochore microtubules polymerize until anaphase then depolymerize.

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Cell Division

Which phase of mitosis is characterized by alignment of chromosomes at the metaphase plate?

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-kinetocho

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17, Metaphase Alignment Mechanisms.

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Cell Cycle Regulation

Which of the following prevents mitotic exit if chromosomes are not properly aligned?

Accurate mitosis demands anaphase initiation strictly after all chromosomes achieve stable amphitelic attachment generating tension. The spindle assembly checkpoint monitors this criterion. Unattached kinetochores catalyze assembly of Mitotic Checkpoint Complex composed of Mad2 locked as C-Mad2, BubR1 ortholog of yeast Mad3, Bub3 and Cdc20 coactivator of APC/C. Within MCC, BubR1 provides pseudosubstrate motif inserting KEN boxes into Cdc20 binding pockets plus direct inhibition of APC/C central cavity, thereby preventing ubiquitination of securin and cyclin B. BubR1 also functions as protein k

Ref: Musacchio, Spindle Assembly Checkpoint Structure of BubR1-MCC, Curr Biol 2015; NCBI Bookshelf, SAC component BubR1.

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