Late Endosome Markers

Late endosomes (LEs) are membrane-bound organelles with a heterogeneous appearance. These compartments serve as central hubs in the endocytic pathway, receiving cargo from early endosomes and directing it to various cellular compartments. LE fusion with lysosomes, autophagosomes, and the trans-Golgi network facilitate receptor trafficking, lysosomal maturation, autophagy, and inter-organelle communication. The specific fate and function of LEs depends on a combination of specific sorting sequences within cargo proteins and upstream signalling events. In cases where cargo is not immediately returned to the plasma membrane via recycling endosomes, early endosomes containing endocytosed material will mature into LEs. Here, LEs themselves are subject to maturation, acquiring lysosomal characteristics in preparation for lysosome fusion. The LE luminal pH is lowered through activation of proton pumps and cargo may be separated into intraluminal vesicles creating a muti-vesicular body (MVB). By maintaining an acidic pH, late endosomes contribute to the efficient degradation of cargo by lysosomal hydrolases. Additionally, LEs can indirectly deliver cargo for lysosomal degradation through autophagosome fusion; an organelle central to the process of macroautophagy. In either case, LE/MVB tethering and fusion is regulated by the small GTPase Rab7, an established marker for these compartments. Not all LEs channel cargo towards lysosomal degradation, instead proteins and lipids may be diverted through retrograde transport. Membrane trafficking in this form can involve direct localisation of MVBs to the plasma membrane where, upon fusion, ILVs are released into the extracellular space as exosomes. Alternatively, cargo may be shuttled back towards the trans-Golgi network by LE-derived tubule-vesicular carriers (TVCs). Formation of these elongated intermediate compartments is facilitated by another GTPase, Rab9, which recruits the retromer complex necessary for cargo detection, packaging and trafficking. While Rab7 and Rab9 are the major markers within late endosomes, other proteins include CD63, LAMP3 and INDOL1. Both CD63 and LAMP3 are enriched in the membranes of LEs, promoting the fusion of MVBs with lysosomes. INDOL1 acts upstream of fusion events, coordinating cargo sorting within ILVs as MVBs begin to form. We offer a range of antibodies against late endosomes markers including Rab7 antibodies and Rab9 antibodies, that are validated across multiple applications, and cover various host species, antibody types, formulations, and conjugates. By investigating the localisation, interaction partners, and regulatory mechanisms of RAB7 and RAB9 in particular, researchers gain a better understanding of late endosome maturation, cargo trafficking, and recycling pathways.