Signaling endosomes: seeing is believing

Signaling compartmentalization provides a highly refined mechanism to specify context-dependent cellular responses. Endosomes are an intracellular membrane-bound compartment that mediates the transport of receptor-bound signaling complexes. Owing to the development of high-resolution microscopy-based imaging techniques it has been possible to demonstrate that endosomes are actively engaged in signal reception and emission. Such observations paved the way to functional studies ascribing indispensable roles for endosomes in orchestrating signals that regulate processes such as cell migration and invasion, asymmetric cell division and differentiation, or intercellular communication.