Intracellular membrane movement and signalling

Our laboratory studies how the yeast lysosome (vacuole) is partitioned between mother and daughter cells during cell division. Yeast have been instrumental in determining the molecular basis of many biological processes in higher eukaryotes. These include events that are unique to complex, multi-cellular organisms. For example several advances in understanding the molecular basis of synaptic transmission came from studies in yeast. Studies of vacuole inheritance in yeast are likely to provide general insight into organelle movement, cell polarization/differentiation and cellular signaling Vacuole inheritance is a highly dynamic, regulated process. In order to identify the molecules required, we developed screens for yeast vac mutants. Studies of these mutants led to our discovery of a vacuole-specific transport complex. This complex is very similar to a complex that moves melanosomes in melanocytes, and synaptic vesicles in neurons. We have recently found that the regulated synthesis and turnover of this complex deposits the vacuole at the correct place at the proper time. We have also discovered a set of mutants that are defective in the phosphatidylinositol 3,5 bis-phosphate signaling pathway. Molecules required for this pathway include Fab1, Vac7, Vac14 and Fig4. Interestingly, while these proteins were first identified in yeast, higher eukaryotes also have genes encoding Fab1, Vac14 and Fig4. We are studying the functions of these human genes. Preliminary data suggests that these genes are essential. Our studies of vacuole inheritance in yeast has provided important clues to:

• The mechanism that allows myosin to associate with its cargo.
• The existence of a higher order regulation of diverse events that happen at a single membrane.
• The importance of phosphatidylinositol 3,5 bis-phosphate (PI3,5P 2) in cell signaling.
• The roles for PI(3,5)P 2 in response to cellular stress.

1. Weisman, L.S. (2006) Organelles on the move; insights from yeast vacuole inheritance. Nature Reviews Molecular Cell Biology (in press)
   
   
2. Pashkova, N., Ramaswamy, S., and Weisman, L.S. (2006) Structural basis for myosin V discrimination between distinct cargoes EMBO J (in press)
   
   
3. Duex, J. E., Tang, F. and Weisman, L.S. (2006) The Vac14p/Fig4p complex acts independently of Vac7p and couples PI3,5P2 synthesis and turnover. J. Cell Biol. (in press)
   
   
4. Tang, F., Kauffman, E. J., Novak, J.L., Nau, J.J., Catlett, N. L. and Weisman, L.S. (2003) Regulated degradation of a class V myosin receptor directs movement of the yeast vacuole. Nature 422:87-92
   
   
5. Pashkova, N., Catlett, N.L., Novak, J.L., Wu, G., Lu, R., Cohen, R.E. and Weisman, L.S. (2005) Myosin V attachment to cargo requires the tight association of two functional sub-domains. J. Cell Biol. 168:359-364
   
   
6. Ishikawa, K., Catlett, N.L., Novak, J.L., Tang, F., Nau, J.J., and Weisman, L.S. (2003) Identification of an organelle-specific myosin- V receptor. J. Cell Biol. 160:887-897
   
   
7. Pashkova, N., Catlett, N. L., Novak, J. L., Wu, G. M., Lu, R., Cohen, R. E., & Weisman, L. S. (2005). Myosin V attachment to cargo requires the tight association of two functional subdomains. Journal of Cell Biology, 168, 359-364.
   
   
8. Ishikawa, K., Catlett, N. L., Novak, J. L., Tang, F., Nau, J. J., & Weisman, L. S. (2003). Identification of an organelle-specific myosin V receptor. Journal of Cell Biology, 160, 887-897.
   
   
9. Tang, F. S., Kauffman, E. J., Novak, J. L., Nau, J. J., Catlett, N. L., & Weisman, L. S. (2003). Regulated degradation of a class V myosin receptor directs movement of the yeast vacuole. Nature, 422, 87-92.
   
   
10. Bonangelino, C. J., Nau, J. J., Duex, J. E., Brinkman, M., Wurmser, A. E., Gary, J. D., Emr, S. D., & Weisman, L. S. (2002). Osmotic stress-induced increase of phosphatidylinositol 3,5-bisphosphate requires Vac14p, an activator of the lipid kinase Fab1p. Journal of Cell Biology, 156, 1015-1028.
    
    
11. Wang, Y. X., Kauffman, E. J., Duex, J. E., & Weisman, L. S. (2001). Fusion of docked membranes requires the armadillo repeat protein Vac8p. Journal of Biological Chemistry, 276, 35133-35140.
    
    
12. Catlett, N. L., Duex, J. E., Tang, F. S., & Weisman, L. S. (2000). Two distinct regions in a yeast myosin-V tail domain are required for the movement of different cargoes. Journal of Cell Biology, 150, 513-525.
    
    
13. Wang, Y. X., Catlett, N. L., & Weisman, L. S. (1998). Vac8p, a vacuolar protein with armadillo repeats, functions in both vacuole inheritance and protein targeting from the cytoplasm to vacuole. Journal of Cell Biology, 140, 1063-1074.
    
    
14. Catlett, N. L., & Weisman, L. S. (1998). The terminal tail region of a yeast myosin-V mediates its attachment to vacuole membranes and sites of polarized growth. Proceedings of the National Academy of Sciences of the USA, 95, 14799-14804.
    
    
15. Bonangelino, C. J., Catlett, N. L., & Weisman, L. S. (1997). Vac7p, a novel vacuolar protein, is required for normal vacuole inheritance and morphology. Molecular and Cellular Biology, 17, 6847-6858.
    
    
16. Hill, K. L., Catlett, N. L., & Weisman, L. S. (1996). Actin and myosin function in directed vacuole movement during cell division in Saccharomyces cerevisiae. Journal of Cell Biology, 135, 1535-1549.
    
    
17. Wang, Y. X., Zhao, H. R., Harding, T. M., deMesquita, D. S. G., Woldringh, C. L., Klionsky, D. J., Munn, A. L., & Weisman, L. S. (1996). Multiple classes of yeast mutants are defective in vacuole partitioning yet target vacuole proteins correctly. Molecular Biology of the Cell, 7, 1375-1389.