A
self-organization model for the transitional endoplasmic reticulum.
Daniel E. Strongin (1), Brooke J. Bevis (1), Jon F. Soderholm (1), Matthias Weiss
(2), Benjamin S. Glick (1)
(1) Molec. Genetics and Cell Bio., University of Chicago, 920 E. 58th St.,
Chicago, IL 60637, USA (destrong@uchicago.edu); (2) Cell Biology and Cell
Biophysics Programme, EMBL, Heidelberg, Germany
Transitional endoplasmic reticulum (tER) sites are morphologically and biochemically distinct ER subdomains that are continuous with the general ER. Secretory cargo is packaged into COPII-coated vesicles at tER sites. Despite this clear structural and functional definition, very little is known about how tER sites are organized at the molecular level. We are using computer simulations coupled with cell biological assays to explore the molecular mechanisms that underlie tER organization and dynamics. Cells of the budding yeast Pichia pastoris have 2-5 discrete tER sites, which can often be followed unambiguously over long periods of time using fluorescence microscopy. We have used 4-D confocal video microscopy to analyze tER dynamics in P. pastoris. These experiments show that tER sites can form de novo and can fuse with one another, suggesting that tER sites are composed of membrane components that self-associate to form patches. We are creating a computational model to test and extend this hypothesis. Additionally, photobleaching experiments using a fluorescently tagged version of the transmembrane tER protein Sec12p have provided the first insights into the exchange of membrane components between individual tER sites. Further in vivo and in vitro experiments are aimed at extending these observations and analyzing the biophysical properties of tER components. The interplay between the computational model and experimental data will improve our understanding of tER dynamics.