The release of peptide hormones or neurotransmitters from neuroendocrine cells is essential for the co-ordination of diverse physiological events. Secretory vesicles derived from the trans-Golgi undergo a complex cycle — including maturation, translocation, membrane docking, and fusion of a subpopulation of vesicles with the cell membrane — but many aspects of vesicle dynamics are still unclear. In the March 13 Nature, Rory Duncan and colleagues at the University of Edinburgh, UK, have addressed at the single vesicle level the key issue of how secretory vesicles are selected for release from the cell, showing that vesicles are segregated in distinct pools according to age (Nature, 422:176-180, March 13, 2003).

Duncan et al. developed a system to track fluorescently labeled large dense-core secretory vesicles (LDCVs) in living, cultured bovine adrenal chromaffin cells (BCCs). Fluorescent labeling of LDCVs was achieved by transduction of BCCs so as to express the...