Localization of Cholecystokinin/Sulfakinin Neuropeptides in Biomphalaria glabrata, an Intermediate Host for Schistosomiasis

Snails belonging to the genus Biomphalaria serve as obligatory intermediate hosts for the trematode Schistosoma mansoni, the causative agent for the most widespread form of schistosomiasis. The simpler nervous systems of gastropod molluscs, such as Biomphalaria, provide advantageous models for investigating neural responses to infection at the cellular and network levels. The present study examined neuropeptides related to cholecystokinin (CCK), a major multifunctional regulator of central nervous system (CNS) function in mammals. A neural transcriptome generated from the CNS of Biomphalaria alexandrina included a transcript encoding two CCK-related peptides, designated Balex-CCK1 (pEGEWSYDY_{(SO 3 H)}GLGGGRF-NH₂) and Balex-CCK2 (NYGDY_{(SO 3 H)}GIGGGRF-NH₂). Peptide expression was examined in Biomphalaria glabrata at the mRNA level using the hybridization chain reaction (HCR) protocol and at the protein level using an antibody against Balex-CCK1. Expression was detected in 60-70 neurons distributed throughout the CNS, as well as in profuse fiber systems connecting the ganglia and projecting to the periphery. CCK-like immunoreactive (CCK_li) fibers were also observed on organs associated with the cardiorespiratory (nephridium, mantle, gill) and male reproductive systems. A comparison of mRNA and peptide localization suggested that CCK expression could be regulated at the level of translation. A potential role of these peptides in mediating responses to infection by larval schistosomes is discussed.