Probing the Endoplasmic Reticulum with Green Fluorescent Proteins

Unlike certain specific organelles found in all animals, the endoplasmic reticulum (ER) does very different things depending on the kind of cell to which it is attached. About the most general you can get is that the rough ER makes various enzymes and receptor sites, while the smoother ER synthesizes cell membrane phospholipids, steroids and other lipids. All cells use the ER for transportation and storage of the various products it synthesizes and much of the lumen volume is simply dedicated to keeping "spare parts" until they are needed. In the digital videos presented above, human osteosarcoma epithelial cells (U2OS line) are expressing a fusion of mEmerald fluorescent protein and an endoplasmic reticulum targeting signal.