Characterisation of two conopressin precursor isoforms in the land snail, Theba pisana

Increased understanding of the molecular components involved in mollusc reproduction may assist in understanding the evolutionary adaptations used by animals, including hermaphrodites, to produce offspring. The neuropeptide conopressin, a member of the vasopressin/oxytocin-like peptide family, can modulate various reproductive activities in invertebrates. In this study, we used the hermaphroditic land snail, Theba pisana, to investigate the presence and tissue-specific distribution of a conopressin gene. Our transcriptomic analysis of T. pisana CNS sheath tissue has revealed two conopressin gene transcripts (Tpi-conopressin-1 and Tpi-conopressin-2), each encoding for precursors containing an identical conopressin nonapeptide and a variable neurophysin. T. pisana conopressins share high identity with other land snails and slugs, as well as other mollusc and vertebrate vasopressin/oxytocin, supported by phylogenetic analysis. Conserved residues in the T. pisana neurophysin are important for peptide binding, and we present molecular dynamic models demonstrating the most likely stable structure of the Tpi-conopressin-1 peptide when associated with neurophysin. RT-PCR shows that Tpi-conopressin-1 is additionally expressed in reproductive tissues, including the dart sac, where abundant spatial expression throughout the sac region is found; this implies a role in 'love' dart synthesis or dart injection during mating. The presence of a conopressin receptor in the CNS sheath indicates CNS neural excitation. In summary, this study represents a detailed molecular analysis of conopressin in a land snail.