1. Characterization of Hydra nematocysts
All cnidarians possess a sensory cell called nematocyte (or cnidocyte). Nematocyst is a specialized organelle of mature nematocyte. So far there are more than 25 structurally distinct nematocysts found in Cnidaria and their roles include the prey capture, the defense and the adhesive locomotion. Most extensive studies of nematocyst are accomplished in Hydra, which has 4 types of nematocysts, namely stenotele, desmoneme, holotrichous isorhiza and atrichous isorhiza. Due to the complex morphology of nematocyst, there are a large number of genes coding for the nematocyst proteins. So far more than 50 nematocyst-specific genes have been identified and among them, 84% have no ortholog in other animals. Current work aims at characterizing these nematocyst-specific genes and their roles in the differentiation process, the structural formation and the sensory transduction.

2. Evolution of nematocyst
Nematocyst is not found in metazoans except the phylum Cnidaria and genes coding for the cytoskeletal structure of nematocysts are also lineage-specific. Nevertheless, a variety of exclusive organelles are also found in some protists. These include trichocyst, mucocyst, toxicyst, haptocyst, rhabdocyst, nematocyst and etc. Among them, the “nematocyst-taeniocyst” of Polykrikos, a heterotrophic dinoflagellate, looks significantly alike to the structure of stenotele of cnidarians. The current knowledge of Polykrikos nematocyst is only based on the morphological studies by transmission electron microscopy. The question arises if there is a common ancestor between the nematocysts of Hydra and Polykrikos. My research focuses on the identification of nematocyst genes from Polykrikos and understanding the evolutionary correlation between the two structures of evolutionary distant species.

3. Nervous system of Hydra
Both nematocyte and nerve cell are differentiated from the interstitial cell lineage of Hydra. Nerve cells are distributed all over the body, at both endoderm and ectoderm. Since Hydra has the simplest nervous system (NS) – a diffused nerve net, it is interesting to disclose NS genes and how they function to make a fundamental nervous system. A comparative approach is taken to identify evolutionarily conserved NS genes in Hydra and further examine their expression patterns. The ultimate goal is to study whether these NS genes perform conserve or diverse functions from those in higher metazoans.

Contact:
Dr. Jung Shan Hwang
Laboratory for DNA Analysis
Center for Information Biology and DDBJ
National Institute of Genetics
Yata 1111, Mishima
Shizuoka 411-8540
Japan
(jhwang@lab.nig.ac.jp)