A mutation in the general membrane trafficking machinery and hydrocephaly.

M embrane fusion is required to deliver specific cargo molecules to distinct intracellular compartments, thereby maintaining the functional and structural organization of eukaryotic cells, as well as intercellular communication, which occurs in precisely timed spatial patterns at the plasma membrane. During embryogenesis, exocytosis is harnessed to induce differentiation and morphogenesis, as demonstrated by the work of Hong et al. in this issue of PNAS (1). Later and throughout life, the temporal control of site-specific fusion coordinates the release and processing of short and long-range messages within an organism.