Kip Sluder received his A.B. from Middlebury College in 1968 andhis Ph.D. from the University of Pennsylvania in 1976. After an AmericanCancer Society post-doctoral fellowship with Dan Mazia at the Universityof California, Berkeley (1977 to 1980), he joined the faculty of the WorcesterFoundation for Experimental Biology in 1981. Since 1990, he has servedas co-director of the Analytical and Quantitative Light Microscopy Courseat the Marine Biological Laboratory, in Woods Hole Massachusetts.In 1997 Kip joined the Cell Biology Department at the University of MassachusettsMedical School as a Professor.
Our research is centered on the mechanisms that control various aspects of cell division. Applying microscopic and biophysical methods, we seek to elucidate the functional properties of control mechanisms as they operate in the living cell. Our results establish the basis for the integration of cell function with advances in the molecular biology of regulatory pathways. We use echinoderm zygotes, frog egg extracts, and cultured cells as model systems.
One of the major projects in the laboratory seeks to elucidate the controls that ensure that the interphase centrosome reproduces, or doubles, only once in each cell cycle in proper coordination with nuclear events. We have recently shown that centrosome reproduction is coordinated with nuclear events by activities that function during S phase of the cell cycle.
We have also developed the first Xenopus egg extract system that supports repeated rounds of centrosome reproduction in vitro. Using this system we have shown that the activity of the cyclin dependent kinase 2- cyclin E complex (Cdk2-cyclin E) is required for multiple rounds of centrosome duplication.
Figure 1: Mammalian cells. (A and B) Overlaid phase and fluorescence images showing BrdU incorporation in mononucleate and binucleate cells. (A) Cells were previously treated with 0.5 µM cytochalasin D and cultured on bare glass. Mononucleate cells have incorporated BrdU, whereas the binucleates have not. (B) Cells treated with 0.5 µM cytochalasin D and cultured on fibronectin-coated glass. Both the mononucleate and binucleate cells have incorporated BrdU. (C) Cells previously treated with 0.5 µM cytochalasin D and cultured on fibronectin-coated glass (images taken from Video 4, available at http://www.jcb.org/cgi/content/full/jcb.200403014/DC1). Frames from a video sequence of two binucleate cells in the same field progressing through mitosis. The first to enter mitosis (top row) divides into two, whereas the second (bottom row) divides into three. Phase-contrast microscopy. Times are in h:min after cytochalasin D removal. Bars, 50 µm.
Figure 2: Repeated rounds of centrosome duplication in an aphidicolin-treated Xenopus egg extract. Frames from a time-lapse video sequence, showing the increase in aster number over time in a microscope field. The decrease in aster number in panel d is due to the migration of asters from the plane of focus and field of view. Minutes after addition of sperm nuclei are seen in the lower right corner of each frame. Polarization optics. 10 microns per scale division.
In other studies we have characterized the cell cycle checkpoint controls for the metaphase-anaphase transition. These checkpoint pathways serve to ensure the equal distribution of chromosomes during cell division. We have demonstrated that signal transducing molecules in the kinetochore monitor chromosome attachment to the spindle and that even one unattached kinetochore will block the metaphase-anaphase transition.
Using GFP-cyclin B and confocal microscopy we are also investigating how the checkpoint pathway that monitors the completion of DNA synthesis controls nuclear envelope breakdown and entry of the cell into mitosis.