March 22, 2013

If there was an NCAA-type bracket of cool things to image in a cell, I’m pretty sure a spindle would make it pretty far in the tournament—if not take the whole thing.  They are extremely photogenic, and their important role and dynamic nature make them a top seed for sure.  Today’s image is from a paper identifying a new player in spindle positioning.

The position of the mitotic spindle serves as the guide to where the cell will be divided into two daughter cells in cytokinesis.  The spindle is positioned with the help of astral microtubules—microtubules that grow from the centrosomes toward the cell periphery.  The interaction of these microtubules with machinery at the cell’s cortex can generate pulling or pushing forces that position the entire mitotic spindle, yet this interaction isn’t completely understood.  A recent paper identifies a protein called MISP as a player in the microtubule-cortex interaction.  Zhu and colleagues found that depletion of MISP, an actin-binding protein, resulted in shortened astral microtubules and rocking, misoriented spindles, among other mitotic defects.  Zhu and colleagues showed that MISP is phosphorylated by Plk1, a major kinase important in many mitotic processes.  The images above show MISP (gray, red in merged images) localization throughout mitosis.  MISP is localized to cortical actin (green).  Boxed regions are shown in higher magnification in the insets.  

Zhu M, Settele F, Kotak S, Sanchez-Pulido L, Ehret L, Ponting CP, Gönczy P, & Hoffmann I (2013). MISP is a novel Plk1 substrate required for proper spindle orientation and mitotic progression. originally published in the Journal of Cell Biology, 200 (6), 773-87 PMID: 23509069