September 24, 2012

If you are a mitotic spindle aficionado or superfan, then you understand how the mitotic spindle has a life of its own. Information on the spindle’s composition, dynamics, and list of duties can fill entire volumes…and there is still so much we are learning about the spindle. Today’s image is from a paper that adds another chapter in our metaphorical mitotic spindle book.

The mitotic spindle is composed of dynamic microtubules and countless proteins that ensure chromosomes are equally segregated into identical daughter cells at the end of cell division. Because much of the structure of the spindle comes from the cytoplasm, the contributions from the nucleus have remained unclear. A recent paper identifies the long-elusive presence of a nuclear matrix—a viscous matrix of proteins that supports the formation and function of the spindle. The nuclear matrix is composed of nuclear proteins that reassemble after nuclear envelope breakdown into a pole-to-pole structure. By looking at the cell divisions in fruit flies, Yao and colleagues found that the nuclear matrix is distinct from spindle microtubules, and is found closely around chromosomes following drug treatments that depolymerized microtubules. The time-lapse images above show mitosis in the syncytial Drosophila embryo. The nuclear matrix (green, Chromator) has a spindle-like morphology as the microtubule spindle (red, tubulin) itself forms. 

Yao C, Rath U, Maiato H, Sharp D, Girton J, Johansen KM, & Johansen J (2012). A nuclear-derived proteinaceous matrix embeds the microtubule spindle apparatus during mitosis. Molecular biology of the cell, 23 (18), 3532-41 PMID: 22855526