Schematic of microRNA transfer by exosomes. (1) microRNAs are selectively incorporated into the intraluminal vesicles of a multivesicular body. (2) Multivesicular bodies fuse with the plasma membrane, therewith secreting their intraluminal vesicles into the extracellular milieu. (3) Exosomes may bind to the plasma membrane of a target cell. Recruited exosomes may either fuse directly with the plasma membrane (4) or first be endocytosed and then fuse with the delimiting membrane of an endocytic compartment. (5) Both pathways result in the delivery of the exosomal microRNA to the cytosol of the target cell where it may associate with and silence corresponding mRNA. Professional illustration by Alice Y. Chen.