Endoplasmic reticulum

The endoplasmic reticulum (ER) is contiguous to the outer nuclear membrane and consists of a membraneous network that is divided into two parts: the rough (rER) and the smooth endoplasmic reticulum (sER). The rER has ribosomes attached to its cytoplasmic surface and is responsible for protein synthesis. Synthesized proteins are controlled for their quality in the rER – misfolded proteins are degraded while correctly assembled proteins can be sent to the Golgi apparatus. The sER is involved in the synthesis of different lipid classes. In addition, the ER is a major storage site for intracellular calcium ions. It is maintaining the Ca2+ homeostasis in the cell by a regulated release and uptake of ions from the cytosol.

Immunofluorescent staining

The ER is recognizable by a network-like staining in the cytoplasm. The network consists of thin tubular strands at the edges of the cell and is denser close to the nucleus. The ER also often shows a similar staining pattern as the nuclear membrane, as both are contiguous to each other.

Read more about the proteome of the endoplasmic reticulum.