Background
All living things are propagated by cell division, the process by which a cell duplicates its contents and divides in two. Of central importance is the transmission of a complete set of chromosomes to each daughter cell, which in eukaryotes is achieved through the function of the mitotic spindle. The long-term goal of the laboratory is to elucidate the principles that underlie spindle assembly and function, and to identify and study the roles of individual proteins involved. Our primary approach is to reconstitute the process in a test tube by preparing functional cellular extracts that can be studied using biochemical and microscopy techniques. In addition, we are developing chemical genetic, proteomic and reconstitution approaches to identify and characterize the key factors important for cell division.
In order to study spindle assembly in vitro, we use eggs from the African frog Xenopus laevis to prepare cytoplasmic extracts that are open to cell cycle regulation, biochemical manipulation and high-resolution microscopy. We have found that plasmid DNA-coated magnetic beads assemble chromatin and function physiologically as "artificial chromosomes", inducing spindle assembly in mitotic extracts in the absence of paired cues such as centrosomes and kinetochores. Using this assay, we have seen that spindle assembly proceeds in two phases: microtubule polymerization and motor-dependent organization (see movies). Magnetic chromatin beads are ideal for characterization of chromatin-associated microtubule nucleation and stabilization activities, and can be used to evaluate how individual motors contribute to the organization of microtubules into a bipolar array. Current projects in the laboratory address the mechanisms behind the dramatic events of spindle assembly and function.
