Epigenomic and transcriptomic analyses reveal cnidocyte specialization in a sea anemone

Cnidarians, including corals, hydras, jellyfish and sea anemones, possess specialized stinging cells called cnidocytes that function in prey capture and defense. These cells represent a striking evolutionary innovation and produce distinct types of organelles such as venom-injecting nematocysts and mechanically entangling spirocysts. While their biomechanics and transcriptional regulation have been studied extensively, little is known about their epigenetic regulation. Here, we combined epigenetic profiling with RNA sequencing in the sea anemone Nematostella vectensis to explore regulatory programs underlying cnidocyte diversity. We identified cell-type-specific H3K27ac-marked regulatory elements in promoter-proximal and distal regions and linked them to distinct gene expression programs. This analysis revealed fundamental differences between nematocytes and spirocytes and uncovered a previously unrecognized nematocyte population that expresses the Nep3 toxin but lacks most other toxins. These findings highlight the complexity of cnidocyte regulation and suggest greater cellular diversity within this defining cnidarian cell type than previously appreciated.