Expression of prohormone convertase 2 and the generation of neuropeptides in the developing nervous system of the gastropod Haliotis

Prohormone convertase 2 (PC2) belongs to a family of enzymes involved in the proteolytic maturation of neuropeptide precursors into mature peptides that act as neurotransmitters, neuromodulators or neurohormones. Here we show that a gene encoding a PC2-like enzyme (HasPC2) is expressed during larval development and in the adult ganglia of the vetigastropod Haliotis asinina. HasPC2 exhibits high sequence identity to other gastropod PC2s and thus is likely to function in peptide processing. Analysis of HasPC2 expression indicates that it is activated early in nervous system development. During trochophore and early veliger larval stages, HasPC2 is expressed in the vicinity of the forming ganglia of the central nervous system and parts of the putative peripheral nervous system. Later in larval development, at the time the veliger becomes competent to interact with the external environment and initiate metamorphosis, HasPC2 expression largely restricts to cells of the major ganglia and their commissures. Profiling of veliger larvae by bioinformatic approaches suggests the expression of a variety of peptides. Direct MALDI-MS-based peptide profiling of juvenile Haliotis cerebral ganglia (brain) reveals an abundance of neuropeptides, including FMRFamide-related peptides and APGWamide, compatible with PC2 functioning in neuropeptide processing in these regions. These results are consistent with PC2 regulating neuropeptide generation in the earliest functioning of the gastropod nervous system.