Cell type-specific expression profiling sheds light on the development of a peculiar neuron, housing a complex organelle

Specialized neurons called cnidocytes define the phylum Cnidaria. They possess an explosive organelle called cnidocyst that is important for prey capture and antipredator defense. An extraordinary morphological and functional complexity of the cnidocysts has inspired numerous studies to investigate their structure and development. However, the transcriptomes of the cells bearing these unique organelles are yet to be characterized, impeding our understanding of the genetic basis of their biogenesis. By generating transgenic lines of the sea anemone Nematostella vectensis using the CRISPR/Cas9 system, we have characterized cell-type specific transcriptomic profiles of various stages of cnidocyte maturation and show that nematogenesis (the formation of functional cnidocysts) is underpinned by dramatic shifts in the spatiotemporal gene expression. We also highlight the stark fall in transcriptional-levels of toxin and structural protein coding genes within cnidocytes with the maturation of capsule. We further reveal that the majority of upregulated genes and enriched biochemical pathways specific to cnidocytes are yet to be characterized. Finally, we unravel the recruitment of a metazoan stress-related transcription factor complex into nematogenesis and highlight its role in the formation of a structural protein of the cnidocyst wall. Thus, we provide novel insights into the biology, development, and evolution of cnidocytes.