Control of metamorphosis and pattern formation in Hydratinia (hydrozoa, cnidaria)

Abstract Hydractinia echinata is a marine colonial hydroid, a relative of the more widely known Hydra. In contrast to Hydra, embryogenesis, metamorphosis and colony growth in Hydractinia are experimentally accessible and therefore, provide an ideal model system for investigating the biochemical basis of pattern formation. In particular, the processes involved in the transformation of the drop‐shaped freely swimming larva into a sessile tube‐shaped polyp are easily monitored, because this transfomation can be induced by application of various substances. Our results indicate that the internal level of S‐adenosylmethionine (SAM), potentially the most important methyl donor in transmethylation processes, plays a key role in the onset of metamorphosis. It is also proposed that the internal level of SAM plays a pivotal role in the proportioning and spacing of polyps within the colony.