Mitotic Spindle Assembly: Building the Bridge between Sister K-Fibers

• Published in: Trends in biochemical sciences (Amsterdam. Regular ed.) Vol. 41; no. 10; pp. 824 - 833
• Main Authors: Simunić, Juraj, Tolić, Iva M.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-10-2016
• Subjects: Animals; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Chromosomal Proteins, Non-Histone - genetics; Chromosomal Proteins, Non-Histone - metabolism; chromosome congression; Gene Expression; Humans; Kinesin - genetics; Kinesin - metabolism; kinetochores; Kinetochores - metabolism; Kinetochores - ultrastructure; Microtubules - metabolism; Microtubules - ultrastructure; Mitosis; overlap microtubules; prometaphase; Spindle Apparatus - metabolism; Spindle Apparatus - ultrastructure; spindle formation; spindle formation; kinetochores; mitosis; prometaphase; chromosome congression; overlap microtubules
• ISSN: 0968-0004; 1362-4326
• DOI: 10.1016/j.tibs.2016.07.004

The mitotic spindle performs the task of physically dividing the genetic material between the newly formed daughter cells. To achieve this, bundles of microtubules and associated proteins orchestrate forces that spatially organize and then separate the chromosomes. In the classic view of the spindle, the kinetochore microtubules (k-fibers) are tensed and, thus, straight, whereas interpolar bundles are curved and do not interact with k-fibers close to the spindle equator. The updated view of the spindle depicts k-fibers as curved and interacting with newly identified interpolar bundles, called bridging fibers, along their length. In this Opinion, we propose and discuss scenarios for the origin of this structure in the context of known spindle assembly mechanisms.
A subset of interpolar fibers, called bridging fibers, connect sister kinetochore-attached microtubule fibers (k-fibers) and balance the force between them.
Most chromosomes in prometaphase begin their congression by lateral interactions with interpolar microtubules, which may become the bridging fiber.
Lateral interactions of kinetochores and interpolar microtubules promote subsequent biorientation by favorable positioning of the kinetochores in the prometaphase spindle.