Dissecting a peptidergic signaling pathway in Trichoplax adhaerens by gene silencing

Trichoplax adhaerens, a simple multicellular marine organism from the phylum Placozoa,^1,2 is one of the most basal metazoan lineages, alongside Ctenophora, Porifera, and Cnidaria.^3,4,5 With its remarkably simple body plan,^6,7Trichoplax provides valuable insights into the evolution of multicellularity.^8,9 Interestingly, despite lacking true tissues and organs, Trichoplax has evolved multiple cell types that can perform coordinated, complex behaviors, including feeding.^10,11,12,13 Peptidergic signaling has been implicated in the regulation of such behaviors,^{14,15,16,17,18,19} though the underlying mechanisms remain poorly understood. A major challenge in investigating these processes has been the lack of established genetic manipulation methods for this organism. In this study, we developed an effective gene knockdown technique using silica nanoparticle-mediated RNA interference (RNAi),^20,21,22,23 which demonstrates superior efficiency and biosafety compared with traditional transfection methods. Using this approach, we confirmed the roles of two ciliary genes in ciliogenesis and identified the function of a classic neuropeptide in regulating feeding behavior. Furthermore, molecular dynamics simulations and knockdown experiments revealed the receptor for this neuropeptide, providing new insights into the coordination of cell movement and feeding in this basal metazoan. Our findings present a novel and effective gene knockdown strategy for Trichoplax, advancing the potential for gene manipulation in marine models and enhancing our understanding of placozoan biology.