C3 in Pomacea canaliculata: a conserved effector with developmental and immune roles

C3 is the central effector of the complement system and one of the most conserved molecules of metazoan innate immunity. Despite its relevance, littleis known about complement components in Lophotrochozoa. Here, wecharacterise the C3 ortholog of the freshwater gastropod Pomacea canaliculata(PcC3) using long-read transcriptomics, phylogenetics, expression profiling andimmunohistochemistry. PcC3 displays a fully conserved domain architecture andclusters phylogenetically in agreement with metazoan relationships. FollowingLPS challenge, PcC3 is up-regulated in haemocytes and unexpectedly in theampulla, but not in the posterior kidney, revealing functional specialization ofimmune tissues. Early developmental transcriptomes reveal strong and sustainedPcC3 activation from 3 to 9 dpf. These data suggest that PcC3 retains canonicalimmune functions but may also contribute to developmental and homeostaticcell clearance, supporting P. canaliculata as a valuable model for complementbiology in molluscs