EUPHYLLIA ANCORA SERIES

Scleractinians, also known as stony corals, are ecologically and economically important marine organisms 17. In the C-terminal region, GLWamides generally possess glycine-leucine-tryptophan (a GLW motif), and the tryptophan residue in the C-terminus is amidated (-Gly-Leu-Trp-NH 2). The proline in the N-terminal structure is known to confer resistance to aminopeptidase digestion 16. For instance, the 7 identified GLWamides in Hydra possess a proline residue at the second position (X-Pro) or at the second and third positions (X-Pro-Pro) in their N-terminal region 8, 10. The mature GLWamides identified in cnidarians to date generally range from 5 to 14 amino acids in length and likely possess conserved structural features in their N- and C-terminal regions 2, 8.

EUPHYLLIA ANCORA SERIES

Preprohormone is posttranslationally processed by a series of proteolytic cleavages and modified to yield mature peptides 8, 10, 14, 15. GLWamides are derived from a larger precursor molecule called preprohormone (also referred to as prepropeptide). Some of these GLWamides have been demonstrated to be involved in a wide range of physiological functions, such as larval metamorphosis 11, muscle contraction (myoactivity) 12, polyp detachment 10, and oocyte maturation and ovulation 2, 13, in cnidarians.

Seven types of GLWamides were later isolated from Hydra magnipapillata 10. GLWamides were first isolated from the sea anemone Anthopleura elegantissima as a trigger of metamorphosis of Hydractinia echinata larvae 9. One of the important neuropeptides identified in cnidarians is the glycine-leucine-tryptophan-amide family neuropeptides (GLWamides, also referred to as LWamides) 8. In cnidarians (hydras, sea anemones, jellies, and corals), more than 40 types of neuropeptides have been identified to date, and the significance of neuropeptides in physiological functions at different stages of life has been demonstrated 2, 6, 7. Neuropeptides act either directly or indirectly as modulators and/or hormones and play important roles in various physiological processes (e.g., growth, reproduction, and metabolism) and behavior in animals 1, 3, 4, 5. Neuropeptides are 3- to 70-amino-acid-long linear polypeptides produced by neurons 1, 2. Our data provide new information on the physiological function of neuropeptides in scleractinians. These results suggest that GLWamides are involved in polyp contraction (myoactivity) in adult scleractinians. Treatment of polyps with synthetic GLWamide peptides induced the contraction of polyps. Treatment of the isolated mouth and tentacles with synthetic GLWamide peptides induced the contraction of these isolated tissues. Immunodetection with an anti-GLWamide monoclonal antibody revealed that GLWamide neurons were mainly distributed in the epidermis of the mouth region and tentacle, in agreement with the distribution patterns of the transcripts. Tissue distribution analysis demonstrated that transcripts of EaGLW preprohormone were mainly expressed in the mouth (including the pharynx) and tentacles of the polyps. The deduced amino acid sequence was predicted to contain six potential GLWamide peptides.

We successfully elucidated the full-length cDNA of GLWamide preprohormone in E. Molecular identification and functional characterization of GLWamides in the adult stony coral Euphyllia ancora were performed. To gain a better understanding of neuronal functions in coral physiology, this study focused on Glycine-Leucine-Tryptophan-amide family neuropeptides (GLWamides), which have been shown to induce muscle contraction and larval metamorphosis in other cnidarians. The existence and function of neurons remain largely unexplored in scleractinian corals.