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Definition
Metamorphosin A (MMA) peptide originally isolated from the anthozoan Anthopleura elegantissima triggers metamorphosis in Hydractinia echinata. Histochemical studies have shown that MMA is a neuropeptide.

Discovery
Leitz et al., have investigated the role of signals and of signal transduction in the development of the marine hydroid Hydractinia echinata. The larvae undergo metamorphosis in response to a chemical signal provided by environmental bacteria. Metamorphosis can be induced by a variety of different compounds interfering with biochemical signal transduction pathways. Sectioned posterior parts cannot be induced by most compounds known to induce whole larvae to metamorphose. They identified a novel peptide, which they named "metamorphosin A” 1.

Structural Characteristics
It is a oligopeptide of composition, pGlu-Gln-Pro-Gly-Leu-Trp-NH21. Peptide signal molecules (<50 amino acid residues) occur widely in animals, and many play important regulatory roles in a variety of physiological processes. Peptides rarely play signaling roles in development. Takahashi et al., developed a novel screening project to systematically isolate peptide signal molecules from a freshwater cnidarian species, Hydra magnipapillata 2.

Mode of Action
MMA  induces isolated posterior parts to undergo metamorphosis and hence reactivates pattern formation, cell proliferation, cell differentiation, and morphogenesis. It is suggested that this peptide is a part of an internal signaling system involved in control of metamorphosis 1. Leitz et al., in 1995 isolated MMA from Anthopleura elegantissima that triggers metamorphosis in Hydractinia echinata. Antibodies directed against the C-terminal part of the molecule immunohistochemically stain neurosensory cells. They assumed that in metamorphosis MMA (or a closely related LW-amide) is an internal signal, transmitted from the anterior to the posterior body parts. Immunoreactivity is also found in ectodermal nerve processes but not cell bodies in the tentacles and in the basal disk of the foot of Hydra magnipapillata. They concluded LW-amide(s) as a neuropeptides 3.

Functions
The metamorphosis of many marine invertebrate larvae is induced by environmental signals. Upon reception of the cues, internal signals have to be set in motion to convey information to all cells of the larvae. When exposed to synthetic MMA, Hydractinia planulae have been shown to undergo either complete or partial metamorphosis; in the latter case, the posterior end of the larva is converted into head structures (tentacles, hypostome, and mouth), whereas the anterior end retains the larval form. Authors used reverse transcriptase (RT)-PCR to examine the correlation between the time-course of induced head formation 5. Cnidarians are among the simplest animals to possess a nervous system. The cnidarians nervous system has been described as a “nerve net” but may also contain nerve rings and other areas of centralization. Cnidarians synthesize monoamines that act as neurotransmitters in other animals including catecholamines and indolamines. LW-amides, including MMA stimulate contraction of some cnidarian muscles and trigger metamorphosis of hydrozoan planulae, While their role in cnidarian physiology has not been fully elucidated, LW-amides have been hypothesized to function in tentacle formation, metamorphosis and larval physiology and. RF-amides affect cnidarian muscle contraction, feeding responses and exfoliation of gamete follicles. The receptors for these peptides have not been identified, but genes encoding preprohormones have been sequenced from several species 6, 7, 8.

References

1.     Leitz T, Morand K, Mann M (1994). Metamorphosin A: a novel peptide controlling development of the lower metazoan Hydractinia echinata (Coelenterata, Hydrozoa).  Dev. Biol., 163(2):440-446.

2.     Takahashi T, Muneoka Y, Lohmann J, Lopez de Haro MS, Solleder G, Bosch TC, David CN, Bode HR, Koizumi O, Shimizu H, Hatta M, Fujisawa T, Sugiyama T  (1997). Systematic isolation of peptide signal molecules regulating development in hydra: LWamide and PW families. PNAS., 94(4):1241–1246.

3.     Leitz T, Marion Lay M (1995). Metamorphosin A is a neuropeptide. Development Genes and Evolution, 204(4):276-279.

4.     Schmich J, Trepel S, Leitz T (1998). The role of GLWamides in metamorphosis of Hydractinia echinata . Development Genes and Evolution, 208(5):267-273.

5.     Mokady O, Dick MH, Lackschewitz D, Schierwater B, Buss LW ,(1998). Over one-half billion years of head conservation? Expression of an ems class gene in Hydractinia symbiolongicarpus (Cnidaria: Hydrozoa). PNAS., 95(7):3673–3678. 

6.     Tarrant AM (2006). Hormonal Signaling in Cnidarians. Ecotoxicology., 1:2-24

7.     Leitz T (2001). Endocrinology of the Cnidaria: State of the art. Zoology-Analysis of

Complex Systems, 103:202-221.

8.      Darmer D, Hauser  F, Nothacker H, Bosch T, Williamson M, Grimmelikhuijzen CJP. (1998). Three different prohormones yield a variety of Hydra-RFamide (Arg-Phe-NH2) neuropeptides in Hydra magnipapillata. Biochem. J., 332: 403-412.

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