Tissue-Specific Venom Composition and Differential Gene Expression in Sea Anemones

Cnidarians represent one of the few groups of venomous animals that lack a centralized venom transmission system. Instead, they are equipped with stinging capsules collectively known as nematocysts. Nematocysts vary in abundance and type across different tissues; however, the venom composition in most species remains unknown. Depending on the tissue type, the venom composition in sea anemones may be vital for predation, defense, or digestion. Using a tissue-specific RNA-seq approach, we characterize the venom assemblage in the tentacles, mesenterial filaments, and column for three species of sea anemone (Anemonia sulcata, Heteractis crispa, and Megalactis griffithsi). These taxa vary with regard to inferred venom potency, symbiont abundance, and nematocyst diversity. We show that there is significant variation in abundance of toxin-like genes across tissues and species. Although the cumulative toxin abundance for the column was consistently the lowest, contributions to the overall toxin assemblage varied considerably among tissues for different toxin types. Our gene ontology (GO) analyses also show sharp contrasts between conserved GO groups emerging from whole transcriptome analysis and tissue-specific expression among GO groups in our differential expression analysis. This study provides a framework for future characterization of tissue-specific venom and other functionally important genes in this lineage of simple bodied animals.