Human Osteosarcoma Cells with mRuby-ER
The endoplasmic reticulum (ER) is an organelle that chiefly functions in the modification of proteins, production of lipids and macromolecules, and distribution of various cellular materials. The ER is comprised of an intracellular membrane system that includes an extensive network of sac-like cisternae and branching tubules. The inner lumen of the ER is quite large, sometimes encompassing 10 percent or more of a cell's total volume. There are generally considered to be two basic types of ER, smooth ER, and rough ER. However, a specialized type of smooth ER, termed sarcoplasmic ER, found in smooth and striated muscle, is sometimes distinguished as a third major type of ER.
Proteins that are moved by the endoplasmic reticulum and from there on through the cell are indicated with a signal sequence, or an address tag. The N-terminal of a protein holds a small number of amino acids that are an address tag, but are detached when the polypeptide arrives at its destination. In the featured digital video sequence, human osteosarcoma cells (U-2 line) are expressing mRuby fused to endoplasmic reticulum.
The red fluorescent protein employed to fluorescently tag the endoplasmic reticulum in the featured digital video, mRuby, is a monomeric derivative of eqFP611, which was originally isolated from a sea anemone. Excitation and emission maxima of mRuby occur at 558 and 605 nanometers, respectively. Similar to its parent protein, mRuby displays a large Stokes shift, but it also benefits from improved intrinsic brightness.