distance

The formation of the mitotic spindle during cell division requires the assembly of microtubules to form a bipolar array that ultimately results in chromosomal segregation. Mechanisms that guide this process are difficult to visualize, but several lines of evidence suggest that chromatin can guide microtubule assembly from a distance. In the September 30 Current Biology, Rafael Carzo-Salas and Eric Karsenti at the European Molecular Biology Laboratory demonstrate that an at-distance effect occurs via signaling gradients that depend on size and orientation of chromatin, which could set up the centrosomal position and ultimately size, shape, and organization of the mitotic spindle (Current Biology, 13:1728-1733, September 30, 2003).

Carzo-Salas and Karsenti used a novel assay system whereby chromatin beads—artificial chromatin aggregates lacking kinetochores—were mixed with human centrosomes in Xenopus oocyte extracts inside a sealed glass chamber that could then be used for microscopic examination and time-lapse video recording. Centrosomal microtubule organization was ...