Endoplasmic Reticulum Structure

Schematic of cell structure with expanded view of the ER

The endoplasmic reticulum (ER) structure is composed from the outer nuclear envelope, and consists of sheets and tubules. Here we describe a variety of labels available to distinguish morphology in both live and fixed cells. These ER labels are highly selective, allowing researchers to identify the ER and follow cellular behavior.

See endoplasmic reticulum stains selection guide

Endoplasmic reticulum introduction

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].

Selection guide for endoplasmic reticulum stains

	ER tracker dyes			ER fluorescent fusion proteins
	ER-Tracker Blue-White DPX	ER-Tracker Green (BODIPY FL Glibenclamide)	ER-Tracker Red (BODIPY TR Glibenclamide)	CellLight ER-GFP, BacMam 2.0	CellLight ER-RFP, BacMam 2.0
Readout	Live cell ER staining			Expression of fluorescent fusion protein
Target	Binds to K+ channels in ER			Protein retained in ER lumen
Common filter set	DAPI	FITC	Texas Red	FITC	TRITC
Labels	ER-Tracker Blue-White	BODIPY FL	BODIPY TR	GFP	RFP
Ex/Em (nm)	374/430-640	504/511	587/615	488/520	555/584
Signal-to-noise ratio
Photostability
Multiplexing	Yes	Yes	Yes	Yes	Yes
Live cells	Yes	Yes	Yes	Yes	Yes
Fixed cells	No	No	No	No	No
Fixable	Yes	Yes	Yes	Yes	Yes
Platform	Imaging	Imaging	Imaging	Imaging	Imaging
Format	1 mM	100 μg	100 μg	1 mL	1 mL
Cat. No.	E12353	E34251	E34250	C10590	C10591
For ER labeling of fixed cells, SelectFX Alexa Fluor 488 Endoplasmic Reticulum labeling kit provides all the reagents required to fix and permeabilize mammalian cells and then specifically label the ER. This kit contains an antibody directed against the ER-associated protein disulfide isomerase (PDI) and Alexa Fluor 488 dye-labeled secondary antibody.

Endoplasmic reticulum tracker dyes

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.

Microscopic image of cells stained with deep red plasma membrane, green ER, red mitochondria, and blue nucleus

Figure 1. Organelle labeling in live cells. Human osteosarcoma (U-2 OS) cells were labeled with CellMask Deep Red plasma membrane stain, the endoplasmic reticulum-selective ER-Tracker Green dye, mitochondrion-selective MitoTracker Red CMXRos dye, and blue fluorescent NucBlue Live Cell Stain. Labeled cells were imaged in the Live Cell Imaging Solution on the Zeiss 710 point-scanning spectral detection confocal microscope.

Microscopic image of cells stained with green mitochondria, red ER, deep red tubulin, and blue nucleus

Figure 2. Organelle labeling in HeLa cells. HeLa cells labeled using NucBlue Live ReadyProbes Reagent, MitoTracker Green FM, ER-Tracker Red, and Tubulin Tracker Deep Red show multiplexing capability and staining specificity. Cells were imaged in Gibco HBSS buffer containing calcium and magnesium, supplemented with 1X Probenecid solution. Images were generated using an EVOS FL Auto 2 Imaging System with an Olympus 60X Super Apochromat Oil objective using DAPI, GFP, Texas Red, and Cy5 EVOS light cubes.

Endoplasmic reticulum fluorescent fusion proteins

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

Microscopic image of cells stained with green ER and blue nucleus

Figure 3. Live cell imaging with CellLight ER-GFP. USOS cells transduced with CellLight ER-GFP. The following day, cells were co-stained with Hoechst 33342 and imaging was performed on live cells using a DeltaVision Core microscope and standard DAPI/FITC filter sets.

Microscopic image of cells stained with red ER, deep red mitochondria, and blue nucleus

Figure 4. Live-cell imaging with CellLight ER-RFP and MitoTracker Deep Red FM. HeLa cells were transduced with CellLight ER-RFP and co-stained with MitoTracker Deep Red FM and Hoechst 33342. Imaging was performed on live cells using a Delta Vision Core microscope and standard DAPI/TRITC/Cy5 filter sets.

Learn more about ER labeling

References

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

Resources

Cell Staining Tool
Fluorescence SpectraViewer—Online tool for visualization of the excitation and emission of fluorescent reagents; allows for checking spectral compatibility for multiple fluorophores.
Cell Structure Information—Find educational resources such as application notes, webinars, videos, articles, and more to cover the use of many of our reagents for identifying cell structures.

BioProbes article