PROTEIN SECRETION IS A CENTRAL ELEMENT OF

lium discoideum culminates with the assembly of a rug-ged, environmentally resistant spore coat around each spore cell. After synthesis, the proteins that will constitute the coat are stored in prespore vesicles (PSVs) until an unknown developmental signal triggers the PSVs to move to the cell surface where they fuse with the plasma mem-brane and secrete their cargo by exocytosis. These events occur synchronously in 80 % of the cells in each develop-ing multicellular aggregate, and thus the system offers a unique opportunity to study the developmental regulation of protein secretion in situ. Proteomic analysis of purified PSVs identified many of the constituent proteins, which in turn has lead to novel hypotheses and new experimental avenues regarding the molecular mechanisms regulatin