When cells are exposed to hormones that act on cell surface receptors, information is processed
through the plasma membrane into the cell interior via second messengers generated in the inner
leaflet of the plasma membrane. Individual biochemical steps along this cascade, starting with ligand
binding to receptors to activation of guanine nucleotide binding proteins and their downstream
effectors such as adenylate cyclase or phospholipase C, have been biochemically characterized.
However, the complexity of temporal and spatial integration of these molecular events requires that
they be studied in intact cells. The great expansion of fluorescent techniques and improved imaging
technologies such as confocal- and TIRF microscopy combined with genetically engineered protein
modules has provided a completely new approach to signal transduction research. Spatial definition
of biochemical events followed with real-time temporal resolution has become a standard goal and
we are breaking the resolution barrier of light microscopes with several new techniques.