Area of Interest
Dr. Salmon has a long standing interest in the cell cytoskeleton and in particular, the mechanisms of mitotic microtubule assembly and chromosome movement. This work has significance because the accurate segregation of chromosomes by the mitotic spindle during cell division is essential to life. Errors produce unequal distribution of the genome resulting in birth defects or cancer. Currently, he is trying to understand how the interactions of kinetochores with spindle microtubules and microtubule motor proteins such as cytoplasmic dynein and CENP-E perform three essential functions in mitosis: 1) attach and orient sister chromosomes to opposite spindle poles; 2) generate forces for congression of chromosomes to the spindle equator prometaphase as well as segregation of the sisters to opposite poles in anaphase; and 3) turn off a "wait anaphase" signal that involves the mitotic checkpoint protein Mad2 to delay the cell cycle machinery until all the chromosomes have become properly attached and oriented on the spindle. Kinetochores are also pulled poleward by the poleward flux of their kinetochore microtubules coupled to depolymerization at the spindle poles. This motility mechanism is unknown, but most likely involves proteins that actively function in maintenance of the spindle pole: gamma-tubulin complexes, cytoplasmic dynein/dynactin, the kinesin-related protein Eg5 and the nuclear protein NuMA.
Dr. Salmon has also actively contributed to the development of new video and digital imaging light microscopy methods for the analysis of microtubule and motor protein dynamics both in vitro and in vivo. He recently developed a new microscopy method call fluorescence speckle microscopy (FSM) that for the first time allows visualization of the motility and assembly dynamics of microtubules within dense arrays like the mitotic spindle. He is using this technique in novel assays of kinetochore and poleward flux motility mechanisms. In collaboration with Kerry Bloom, he has been able to combine the power of digital imaging with green fluorescent fusion proteins to make budding yeast a very powerful genetic model system for addressing fundamental function questions related to how microtubule dynamics and motor proteins generate nuclear movements and mitosis.
The Salmon lab has several high resolution light microscopes: a VE-DIC optical bench microscope for video assays of microtubule dynamic instability in vitro (Salmon, E. D., and P. Tran. 1998. High resolution video-enhanced differential interference contrast (VE-DIC) light microscopy. Methods in Cell Biol. 56: 153- 184.); a multimode, multiwavelength fluorescence microscope which uses a cooled CCD and the mteaMorph digital image processing system to obtain 4-D images of living and fixed cells where DNA and proteins are labeled with different fluorescent probes (Salmon, E. D., S. L. Shaw, J. Waters, C. M. Waterman-Storer, P. S. Maddox, E. Yeh, and K. Bloom. 1998. Methods in Cell Biol. 185-215.); lasers for photobleaching marks on lluorescent structures to measure dynamics; several MetaMorph oif-line systems (PC computers) for image and data analysis (e.g. microtubule tracking); and a Tektronics dyesublimation printer for hardcopy of digital images. The Biology Department has a microscope resource containing a Zeiss Transmission electron microscope and a Zeiss laser scanning confocal fluorescence microscope.