Investigators and Program Directors

Research Interests

During mitosis chromosomes undergo a complex series of movements that culminate in the migration of sister chromatids to opposite poles of the mitotic spindle. This orderly migration is necessary to ensure that newly forming daughter cells each receive a full complement of DNA. The mitotic spindle is constructed from microtubules (MTs), a subset of which attach to chromosomes at a specialized region known as the kinetochore. After each kinetochore from a pair of sister chromatids binds to the spindle, the chromosome migrates to the spindle equator where it awaits separation of sister chromatids at anaphase onset. Recent studies from several laboratories demonstrate that the kinetochore is the primary site of force generation for chromosome motion, and the site of a cell cycle checkpoint that delays anaphase until all chromosomes are attached to the spindle. My laboratory is using video light microscopy, same cell correlative light microscopy and electron microscopy, and 3-D reconstruction methods, to gain structural insight into interactions between the kinetochore and kMTs that produce and control bidirectional chromosome motions. We are also using immuno-electron microscopy to localize proteins found near the kinetochore. Thus far we have extensively characterized the number of kMTs per kinetochore on PtK1 cells throughout mitosis. The kMT number has been postulated to be a regulator of the direction of motion, and is thought to be critical for release from the anaphase checkpoint. Our 3D tomographic reconstructions suggest that the location of kMT ends varies with the direction of chromosome motion. If this latter observation is verified, it will provide an important clue about force generation and control of the direction of motion.

A second major research interest in my laboratory is microtubule based motility. Currently, in collaboration with Dr. Michael Koonce of the Wadsworth Center, we are investigating the ultrastructure of microtubule motor cytoplasmic dynein and its interaction with the microtubule lattice. Cytoplasmic dynein is a large mechanochemical ATPase (500 kDA in mass, approximately 11 nm in diameter) responsible for retrograde transport along microtubules. It also has critical functions during mitosis. We are initiating studies to determine the ultrastructure of the free and bound forms of dynein at moderate resolution (2 nm). Since Dr. Koonce has cloned the molecule we can compare native structure to structure with appropriate tag insertions and sequence alterations. We also plan to study dynein structure in the presence of ATP analogues to simulate different stages in the mechanochemical cycle.

Contact Information

E-mail: bruce@wadsworth.org.

Wadsworth Center's Featured Image - June 2002 -- Location of centromere protein E (CENP-E) in human lung cells