Elucidating the role of Ran.  In collaboration with the laboratory of Karsten Weis, we are studying one pathway important for spindle assembly that depends on the small GTPase Ran.  Analogous to its role in interphase nucleocytoplasmic transport, RanGTP generated by the chromatin-bound guanine nucleotide exchange factor RCC1 in mitosis functions to locally discharge cargoes from transport factors in the vicinity of chromosomes that promote spindle assembly.  We have used fluorescence energy transfer (FRET) probes to demonstrate a physical gradient of RanGTP and a released cargo surrounding mitotic chromosomes, and are identifying and functionally characterizing the many downstream effectors of this pathway.

Chromosome architecture and cell division.  Chromosomes play a critical role in their own transmission, yet the mechanisms determining their higher order organization and mitotic functions are not understood.  We are evaluating the roles of several factors including condensin, cohesin, and histone H1 in chromosome condensation and segregation, using microscopy, biochemical and biophysical approaches.

Using chemical and proteomic approaches to identify cell division factors and elucidate pathways.  We have combined phenotypic screening of chemical libraries with affinity chromatography in Xenopus egg extracts to identify compounds that disrupt spindle assembly and their molecular targets.  In a more directed approach, we are screening for inhibitors of the Ran pathway using a FRET assay.  Taking advantage of the latest advances in proteomic techniques, we are isolating subcellular structures from dividing mammalian cells, including the cell division remnant (midbody) and mitotic chromosomes to identify constituent proteins, whose function is then evaluated by RNA interference (RNAi) techniques.