What happens when you bake a cake without baking powder? That’s right…you get a flat, dense cake-shaped hockey puck. What about too much baking powder? Kablooey…the cake rises quickly then deflates. Approaching questions in cell biology this same way leads to amazing discoveries about cells, minus the cake. Today’s image is from a paper describing the roles of different dynactin subunits.
Dynactin is a multi-protein complex that is essential for the activity and binding of dynein, the microtubule motor. It has been suggested that dynactin is the key to dynein’s ability to bind countless different cellular cargoes throughout every stage of the cell cycle. Of the 11 subunits in dynein, 4 proteins (Arp11, p62, p27, and p25) make up the “pointed end complex,” a domain believed to be important in cargo specificity. A recent paper shows results on the importance and interactions of these pointed end complex proteins. By depleting levels—or overexpressing—these proteins in tissue culture cells, Yeh and colleagues found that p62 and Arp11 pair up and affect dynactin binding to the nuclear envelope prior to mitosis, while p27 and p25 pair up to regulate membrane binding (early and recycling endosomes). Yeh and colleagues also found that Arp11 and p62 are necessary for dynactin stability. In the images above, mitotic spindles lacking different subunits of the pointed end complex show various defects. The spindles (red, microtubules) of cells lacking Arp11 and p62 are multipolar, as compared to wild-type cells (top row). Spindles of cells lacking p27, however, appeared normal.
Yeh TY, Quintyne NJ, Scipioni BR, Eckley DM, & Schroer TA (2012). Dynactin's pointed-end complex is a cargo-targeting module. Molecular biology of the cell, 23 (19), 3827-37 PMID: 22918948