Cells need to react to environmental changes and maintain a balanced system of signaling cascades within the cell. Proteins outside of the cell, on the cellular surface, inside the cellular membrane, and within the cell orchestrate many fine-tuned signaling pathways, which result in reactions to environmental conditions or changes in the organism itself. The spatio-temporal organization of cellular processes like cell signaling, cell polarization and neurite outgrowth are often regulated by the subcellular distribution of molecules or organelles.