Regulatory mechanisms in metamorphosis of the serpulid polychaete Hydroides elegans (Haswell).

摘要

The focus of this study is an examination of the fundamental steps involved in the progress of metamorphosis in the tropical serpulid polychaete Hydroides elegans. Competent larvae of H. elegans metamorphose rapidly following induction by common marine biofilms. Metamorphosis is characterized by initial secretion of a primary tube, followed by a series of morphogenetic changes that include the loss of the prototroch, differentiation of the collar and thoracic membrane, and differentiation of the tentacular crown. Following these changes is secretion of the secondary, calcareous tube. The secondary tube consists of an organic matrix with an amino acid composition different from the primary tube, it functions to protect the adult worm secure it to the substratum. The metamorphic response in H. elegans can be artificially induced with the monovalent cations Cs+ and K+. This response, found to be concentration and time-of-exposure dependent, is much slower than the metamorphic response to biofilms. In further experiments, metamorphosis was shown to progress in the presence of transcription and translation inhibitors (DRB or emetine) to the stage where branchial radioles begin to differentiate, with any of the metamorphic cues. Primary tube production occurs at the onset of metamorphosis and requires little or no de novo transcription or translation. The amino acid composition of the primary tube was found to be high in glycine, a characteristic shared by adhesive proteins produced by various other invertebrates. The primary tube provides initial attachment during metamorphosis, but is not necessary for formation of the secondary, calcareous tube. With the availability of cDNA libraries constructed from various developmental stages of H. elegans, we now have a direct means with which to investigate families of genes involved in tube secretion as well as other genetically controlled developmental processes.