Endoplasmic Reticulum Structure

The endoplasmic reticulum (ER) is found in all eukaryotic cells and is the largest organelle, consisting of more than half the total membrane content. Its structure is a continuation from the outer layers of the nuclear membrane, consisting of sac-like sheets called cisternae, and branched tubules [1]. The flattened sac-like sheet come in two forms: membrane bound by ribosomes (rough ER) or unbound by ribosomes (smooth ER). The ER has a central role in lipid and protein synthesis, protein chaperoning and folding, and calcium homeostasis [1].

ER-Tracker dyes are highly selective, cell-permeant, live cell endoplasmic reticulum stains. At low concentrations, these dyes have not been shown to be toxic to cells. When cells are stained using the protocol provided, the ER staining pattern is partially retained after fixation with formaldehyde.

ER-Tracker Blue-White DPX is highly selective and photostable. It has an excitation ~374 nm and is environment sensitive resulting in an emission range from 430 nm to 640 nm. While a standard DAPI filter works best and is recommended, a UV longpass filter can be used when visualizing ER staining.

ER-Tracker Green (Figure 1) and ER-Tracker Red (Figure 2) stains, BODIPY FL glibenclamide and BODIPY TR glibenclamide, respectively, are fluorescent sulfonylureas. These ER stains are targeted using glibenclamide, which binds to the sulfonylurea receptors of ATP-sensitive K⁺ channels that are prominent on the ER; however, they may have more disseminated tissue- and cell type-dependent distributions. It is important to note that the pharmacological activity of glibenclamide could potentially affect ER function.

CellLight fluorescent fusion proteins can be used for endoplasmic reticulum staining, allowing for identification and demarcation of the ER in live cells and to follow the dynamics of cellular behavior. CellLight ER-GFP (Figure 3) and CellLight ER-RFP (Figure 4) are ready-to-use constructs that express fluorescent proteins with ER-retention signals from calreticulin (1.8 kDa, N-term), a resident protein of the ER lumen, and KDEL (0.5 kDa, C-term). These fusion proteins are highly specific since localization is directed by cellular protein trafficking.

Introducing CellLight fluorescent fusion proteins involves a simple transfection step using the BacMam technology, and they work like cell stains with minimal toxicity or chemical disruption. These ER fusion proteins are compatible with other fluorescent probes for multiplex analysis in live cells, or after formaldehyde fixation for colocalization studies.

Learn more about these and other CellLight fluorescent proteins

Learn more about ER labeling

References

1. Schwarz DS and Blower MD (2016). Cell Mol Life Sci. 73:79-94. PMID: 26433683.