Abstract
Sea anemones vary immensely in life history strategies, environmental niches and their ability to regenerate. While the sea anemone Nematostella vectensis is the starlet of many key regeneration studies, recent work is emerging on the diverse regeneration strategies employed by other sea anemones. This manuscript will explore current molecular mechanisms of regeneration employed by non-model sea anemones Exaiptasia diaphana (an emerging model species for coral symbiosis studies) and Calliactis polypus (a less well-studied species) and examine how these species compare to the model sea anemone N. vectensis. We summarize the field of regeneration within sea anemones, within the greater context of phylum Cnidaria and in other invertebrate models of regeneration. We also address the current knowledge on two key systems that may be implemented in regeneration: the innate immune system and developmental pathways, including future aspects of work and current limitations.
Highlights
Cnidarians are an ancient extant group, with estimates placing the phylum’s emergence at 740 million years ago and their divergence from its sister-lineage Bilateria at approximately 635–542 mya [1,2,3]
This initiation and early recruitment of novel genes during regeneration is mirrored in Hydra; it was shown that cnidarian-specific novel genes (15/382 novel genes identified were active during regeneration) are recruited in the early stages of regeneration and conserved genes are recruited later in the response [66]
Very few sea anemones outside of Nematostella have been observed with multiple ‘crowns’, but this is inducible in some sea anemones by introducing a small transverse incision of sufficient depth into the body column, which may or may not result in complete transverse fission in some species. This mechanism illustrates an interesting overlap between regeneration and development strategies in sea anemones, and further highlights the diverse evolutionary and life history strategies that occur in phylum Cnidaria
Summary
Cnidarians (jellyfish, corals, sea anemones and hydrozoans) are an ancient extant group, with estimates placing the phylum’s emergence at 740 million years ago (mya) and their divergence from its sister-lineage Bilateria at approximately 635–542 mya [1,2,3]. Sea anemones (Cnidaria: Anthozoa: Actiniaria) encompass approximately 1200 species and are soft-bodied, mostly sedentary, primarily marine-dwelling invertebrates [21] They are an evolutionary ancient extant group, with estimates placing the divergence of the model sea anemone Nematostella (family Edwardsiidae), from other actiniarians between 400–600 mya [22]. Sea anemones exhibit multiple defensive strategies to avoid or deter predators, including behavioral (e.g., moving or swimming away) [27,28] and envenomation of predators, through the firing of venom-filled cnidocytes which are distributed throughout their body plan [29,30,31] These strategies do not always entirely deter predators, several predator species (e.g., nudibranchs) have evolved the ability to ‘steal’ cnidocytes through ingestion of cnidarian species and can repurpose these cells for their own defense [25,32]. We explore the role of two major systems that many studies speculate may be implemented in regeneration: the innate immune system and developmental pathways
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