EST and genome projects have been/are being carried out for organisms ranging from bacteria to yeast among single-celled organisms to a variety of plants and animals among multicellular organisms. The Cnidarian Genetic Toolkit Project will be the first such project involving non-bilaterian metazoans. The goal of the Project is to generate large EST datasets and arrayed cDNA libraries for two hydrozoans, Hydra magnipapillata (105 strain) and Podocoryne carnea. These two cnidarians have been chosen because both are easily cultured in the laboratory, which has led to a detailed understanding of their biology. In addition, molecular methods are well-established for both organisms. Finally, each of the two organisms has advantages for the three questions the Project will address.
One of the issues to be addressed by the Project concerns the definition of the gene set that is common to, or defines a metazoan. Examination of the gene set of a basal metazoan provides a useful approach to this question. Cnidarians are valuable in this regard as next to sponges they are the most basal group of metazoans. But, unlike sponges, they have many of the characteristics of more advanced metazoans such as a well-defined body plan and a nervous system. Using bioinformatic methods, it is likely that about 30-50% of the ESTs will be identified as homologues of specific genes or as belonging to a particular class of genes. By comparing the cnidarian gene sets with the gene sets of single-celled and multicellular metazoans, we will gain information about subsets of genes common to metazoans, which will help define the gene set of a metazoan. Further, subsets found in advanced metazoans, but in neither of the two cnidarians would provide information on the evolution of the metazoan gene set.
A second issue concerns the damage done to marine organisms, in particular corals, by rising temperatures. Hydra, as do other organisms, reacts to an increased culture temperature by increased synthesis of Hsp70, a stress-response protein. A more detailed understanding of the set of genes that are up-regulated in response to temperature stress will be useful, as some of the genes could be used to develop assays for measuring the extent of the stress that, say, a coral reef is experiencing. In particular, some of these genes could serve as the basis for assays for early indication of stress before more visible effects are apparent. By subjecting Hydra to a range of temperatures and making use of the set of Hydra ESTs and microarray analysis, a set of genes will be identified that respond to increased temperatures as well as a subset that are particularly responsive to minor increases. Not only will this extend the understanding of genes that are involved in stress response, but some of them could be used for the described assays.
The third question focuses on the sets of genes required for the development of specific morphologies. Podocoryne, a colonial hydrozoan, has both a polyp and a medusa life cycle stage. The morphologies of these two stages are quite different. By carrying out microarray analysis using the Podocoryne EST set, and mRNA isolated from either the polyp or the medusa stage, the set of genes expressed in each stage will be determined. A detailed comparison of the two subsets of genes will lead towards determining to what extent the two stages are built/composed with different or with similar subsets of genes. In turn, this will provide insight as to whether different life cycle forms in cnidarians are based on different gene sets, or on different regulation of similar gene sets.
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