Abstract
The endoplasmic reticulum (ER) has dynamic structures; i.e., the polygonal network composed of sheets, tubules, and "three-way junctions". To identify the factors responsible for ER morphology, we isolated the mutants that showed defects in ER morphology, and designated them endoplasmic reticulum morphology (ermo). ermo1 and ermo2 developed a number of ER-derived spherical structures, while ermo3 developed a large aggregate within the cells. The spherical structures in ermo2 also formed a large aggregate. In ermo1 and ermo2, the genes involved in COPI and COPII formation, respectively, were mutated. However, we could not find any defects of membrane trafficking in these mutants, suggesting that ERMO1 and ERMO2 have a novel function in maintaining ER morphology. Alternatively, it is possible that ER-Golgi transport plays a crucial role in ER morphology. In addition, ERMO2 and ERMO3 were shown to be required for keeping organelles distributed throughout the cells.
