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Role of ER in the Secretory Pathway

Role of ER in the Secretory Pathway

Eukaryotic cells have a special pathway that enables communication between various intracellular membrane-bound compartments and also with the extracellular environment. This pathway is termed as the secretory pathway.
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About a third of proteins synthesized in the cell are sorted via the secretory route. They shuffle between different compartments in membrane-bound vesicles until they reach their final destination. The main intracellular compartments involved...

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Secretory vesicles, also known as dense core vesicles (DCVs), are membrane-bound vesicles that transport secretory proteins, such as hormones or neurotransmitters. Regulated secretory vesicles transport proteins from the trans-Golgi network to the exterior of the cell. Proteins present in regulated secretory vesicles are required to be rapidly exocytosed in large amounts upon a specific stimulus.
Various proteins regulate the aggregation of molecules inside the secretory vesicles. Chromogranins...

Exocrine Glands: Methods of Secretion

Exocrine Glands: Methods of Secretion

Exocrine glands are those that release their secretions through ducts. Based on their mode of secretion, they can be classified into merocrine, apocrine, and holocrine.
Merocrine Secretion
Merocrine secretion is the most common type of exocrine secretion. The secretions are enclosed in vesicles and moved to the cell's apical surface, where the contents are released by exocytosis. For example, mucous, a watery secretion rich in the glycoprotein mucin, is a merocrine secretion. The eccrine glands...

Vesicular Tubular Clusters

Vesicular Tubular Clusters

After budding out from the ER membrane, some COPII vesicles lose their coat and fuse with one another to form larger vesicles and interconnected tubules called vesicular tubular clusters or VTCs. These clusters constitute a compartment at the ER-Golgi interface known as ERGIC (Endoplasmic Reticulum Golgi Intermediate Compartment). The ERGIC is a mobile membrane-bound cargo transport system that sorts proteins secreted from ER and delivers them to the Golgi.
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Endoplasmic Reticulum

Endoplasmic Reticulum

The Endoplasmic Reticulum (ER) in eukaryotic cells is a substantial network of interconnected membranes with diverse functions, from calcium storage to biomolecule synthesis. A primary component of the endomembrane system, the ER manufactures phospholipids critical for membrane function throughout the cell. Additionally, the two distinct regions of the ER specialize in the manufacture of specific lipids and proteins.

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Related Experiment Video

Updated: May 24, 2026

Visualization of Endoplasmic Reticulum Subdomains in Cultured Cells

Visualization of Endoplasmic Reticulum Subdomains in Cultured Cells

Published on: February 18, 2014

ERES (ER exit sites) and the "secretory unit concept".

M Langhans¹, T Meckel, A Kress

¹Department of Plant Cell Biology, Centre for Organismal Biology, University of Heidelberg, Germany.

Journal of Microscopy

|February 25, 2012

Summary

In higher plants, COPII proteins are found near Golgi stacks, not the endoplasmic reticulum (ER) surface. This challenges the "secretory unit" model of ER-Golgi transport.

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Area of Science:

Plant cell biology
Molecular and Cellular Biology
Biochemistry

Background:

The plant Golgi apparatus comprises numerous mobile stacks interacting with the cortical ER.
Transport between the ER and Golgi is mediated by COP-coated vesicles.
Previously, ER exit sites (ERES) were identified by COPII protein localization, suggesting association with Golgi stacks.

Purpose of the Study:

To investigate the precise localization of COPII proteins in higher plants.
To re-evaluate the existing model of ER-Golgi transport and the concept of the "secretory unit".

Main Methods:

High-resolution confocal laser scanning microscopy (CLSM) of tobacco leaf epidermis.
Utilized a novel COPII marker and YFP-SEC24, a known COPII coat protein.

Main Results:

COPII fluorescence was observed associated with Golgi stacks, not the ER surface.
This fluorescence likely represents transient accumulation of COPII vesicles within the Golgi matrix before cis-Golgi fusion.
Calculations indicate a low number of COPII vesicles (<20) are sufficient for the observed signal.

Conclusions:

The findings challenge the established view of ER exit sites being intimately associated with Golgi stacks.
The data suggests the