Endosomes are formed from:
Endosomal system is central node of vesicular traffic that integrates endocytic and biosynthetic routes to sort cargo after internalization or secretion. Classical early endosomes originate when clathrin-coated pits invaginate with assistance of AP2 adaptor, epsin and dynamin GTPase scission, or when caveolae containing caveolin internalize, delivering extracellular ligands, nutrient receptors such as transferrin receptor, signaling receptors like EGFR, and fluid-phase markers into cell. These primary vesicles rapidly lose coat through auxilin and Hsc70 and fuse homotypically via Rab5-GTP, EEA
Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 13: Endosome Formation from Plasma Membrane and TGN.
