The Importance of GLWamide Neuropeptides in Cnidarian Development and Physiology

The peptide-signaling molecules (<50 amino acid residues) occur in a wide variety of invertebrate and vertebrate organisms, playing pivotal roles in physiological, endocrine, and developmental processes. While some of these peptides display similar structures in mammals and invertebrates, others differ with respect to their structure and function in a species-specific manner. Such a conservation of basic structure and function implies that many peptide-signaling molecules arose very early in the evolutionary history of some taxa, while species-specific characteristics led us to suggest that they also acquire the ability to evolve in response to specific environmental conditions. In this paper, we describe GLWamide-family peptides that function as signaling molecules in the process of muscle contraction, metamorphosis, and settlement in cnidarians. The peptides are produced by neurons and are therefore referred to as neuropeptides. We discuss the importance of the neuropeptides in both developmental and physiological processes in a subset of hydrozoans, as well as the potential use as a seed compound in drug development and aspects related to the protection of corals. 1. Introduction Peptide-signaling molecules (<50 amino acid residues) have been found in a wide variety of organisms and many are known to play important roles in regulating physiological processes in both vertebrates and invertebrates. For example, peptide-signaling molecules act as neurohormones in the endocrine system and as neurotransmitters or neuromodulators in the nervous system. In addition, individual neuropeptides have been found to be multifunctional and may be involved in the immune response, developmental processes, and physiological processes within a single organism. The action of these peptides has been found to be spatio-temporally regulated, which ensures that the timing and pattern of development proceed correctly and that viability is maintained. Among metazoan organisms, the freshwater cnidarian Hydra (Figure 1(a)) has one of the most primitive nervous systems. The nervous system of the Hydra is generally regarded as a diffuse, net-like structure that extends throughout the animal (Figure 1(b)). This “nerve net” is composed of two morphologically distinct cell types, ganglion cells, and sensory cells [1]. To date, a variety of neuropeptides have been identified in Cnidaria. For example, the GLWamide-family peptides that have been isolated from the sea anemone, Anthopleura elegantissima [2], and Hydra magnipapillata [3] have been shown to induce the metamorphosis of