Multiple neuropeptides derived from a common precursor are differentially packaged and transported

The ELH prohormone is proteolytically processed into at least nine peptides which govern egg-laying behavior in Aplysia. Quantitative immunocytochemistry demonstrates that peptides derived from the prohormone are packaged into distinct vesicle classes. Further experiments suggest the segregation occurs via a rapid initial proteolytic cleavage of the prohormone followed by sorting at the trans Golgi. Egg-laying hormone (ELH) immunoreactivity is localized to the cell body and processes, while bag cell peptide (BCP) immunoreactivity is greater in the cell body. Steady state levels of the amino-terminal set of peptides including the BCPs are 3- to 8-fold lower than the carboxy-terminal cleavage products, such as ELH. Thus, intracellular packaging and routing of the peptides cleaved from a single prohormone regulate their localization and levels in these neurons.