Large dense cored vesicles are enriched in neuropeptide processing intermediates in the Aplysia bag cells

The bag cell neurons in the marine snail Aplysia synthesize large amounts of the egg-laying hormone (ELH) prohormone. The ELH precursor is proteolytically processed into 9 peptides making this a useful system for studying prohormone processing and the sorting of proteins destined for the secretory pathway. The peptides derived from the ELH prohormone are differentially packaged into four distinct classes of dense cored vesicles (DVCs). Dense cored vesicles in the large class are greater than 250 nm in diameter, contain the 6 peptides derived from the aminoterminus of the prohormone and are localized to the cell soma and not the neuronal processes. Here we demonstrate that the large DCVs are enriched in prohormone processing intermediates. In addition, many of the large DCVs do not contain acid phosphatase activity suggesting they are an organelle distinct from the lysosomes and that different classes of DCVs may subserve unique functions within the secretory pathway.