Endosomal Markers

Endosomes represent a group of membrane-bound vesicles which serve as cargo sorting, processing and recycling stations, as well as centres of intercellular communication. Different proteins and functions are associated with specific endosomal compartments; namely: early endosomes; late endosomes; multivesicular bodies (MVBs); and recycling endosomes. Early Endosomes (EEs) act as the gatekeepers of vesicle sorting and recycling. Biogenesis starts at the cell surface following invagination of the plasma membrane to create an endocytic vesicle. These vesicles shed protein coats and fuse together as part of the EE maturation process. Rab5, a small GTPase protein, plays a crucial role in their formation and maturation. It controls vesicular trafficking, fusion events, and cargo sorting, ensuring the proper delivery of internalised molecules. EEs are also marked by EEA1, a tethering protein that facilitates fusion with incoming endocytic vesicles. Late Endosomes (LEs) serve as a sorting hub for intracellular cargo destined for different intracellular compartments. Certain LEs mature into lysosomes, specialised and acidified compartments critical for the degradation and turnover of cellular biomass. LAMP1, a lysosome-associated membrane protein, marks the membrane of late endosomes and lysosomes, contributing to their structural integrity. During this maturation process proton pumps are activated, lowering the luminal pH and critical hydrolase enzymes (nucleases and proteases) are delivered into the compartment. The latter can be achieved, both, by kissing fusion with transport vesicles, and fusion with pre-existing lysosomes. Rab7, another GTPase protein, regulates the trafficking of LEs and their fusion with lysosomes. Pallidin, an adaptor protein, interacts with Rab7 and is involved in LE maturation. Other LEs mature into MVBs through inward budding of the compartment membrane, creating intralumenal vesicles (ILVs). MVBs facilitate the degradation of cargo both independently and through fusion with lysosomes. Alternatively, some MVBs fuse with the plasma membrane, releasing ILVs as exosomes. CD63, a tetraspanin protein, is present on both MVBs and exosomes, serving as a marker for these structures. It acts as a key regulator in intercellular communication and cargo sorting within the MVB pathway. Additionally, Alix, a protein involved in MVB biogenesis promotes efficient ILV formation. Recycling endosomes (REs) specialise in the retrieval and recycling of specific molecules back to the cell surface. Rab4 coordinates the recycling pathway and maintains cellular membrane composition. Rab11 regulates the recycling of membrane proteins. Both REs and LEs contribute towards retrograde vesicular transport. While REs mainly recycle membrane components to the cell surface, LEs traffic cargo towards the Golgi apparatus and endoplasmic reticulum. We offer a range of antibodies against endosomal markers, including Caveolin-1 antibodies, Caveolin-2 antibodies, EEA1 antibodies, EGFR antibodies, and Rab5A antibodies, which can help researchers understand endosome localisation, dynamics and morphology. These reagents are powerful tools for studying the internalisation and transport of protein cargo or receptor-ligand complexes internalised during endocytosis. These reagents have been validated across multiple applications and cover various host species, isotypes, formats and conjugates.