Gene expression and regulation of Aplysia californica prohormone convertases aPC1B and aPC2.

Peptide diversity can be regulated in many ways. One of the possible mechanisms of such a regulation may lie in the differential processing of a precursor in a tissue-specific manner or in a modulated processing within a single cell. To address these questions the enzymes responsible for the release of active neuropeptides first need to be well characterized. In this study, we have established the cellular distributions of the recently cloned prohormone convertases aPC2 and aPC1B in Aplysia californica and found the distribution of these enzymes to be mainly neuronal and endocrine. We then investigated in two sets of neurons (bag cell neurons and sensory neurons) the possible regulation of these two prohormone convertases by a neurotransmitter known to modulate behavior in Aplysia. In these neurons, we found that only aPC2 is regulated by serotonin possibly via the cyclic AMP cascade. Finally, a study of the biosynthesis of the bag cell egg-laying hormone precursor after treatment with serotonin suggests that such a treatment may increase its processing.