B. Aerne, H. Gröger, P. Schuchert, J. Spring and V. Schmid
In the metagenic life cycle of hydroidans, the sexual stage, the medusa is produced by a budding process from the polyp generation. Compared with the polyp stage the medusa is structurally and anatomically more differentiated. This is reflected in the presence of sense organs and cell types not present in the polyp stage. Attempts were made to analyze the differences between the two stages at the molecular level. For this reason the RNA expression pattern was compared between polyp and medusa of Podocoryne carnea M. Sars with the RNA fingerprinting technique. Comparing RNA fingerprints of polyp and medusa we showed that 84% of the analyzed RNA fragments were expressed in both stages, whereas 7% were specific for the polyp and 9% for the medusa stage. These results are compared with observations made earlier at the protein level. A gene specifically expressed in polyps is represented by the Pol-1 cDNA. This cDNA was obtained from a differential screening of a cDNA library for life stage specific genes and further characterized. The deduced amino acid sequence of Pol-1 suggests that the translation product is a small secreted protein. Expression studies demonstrate that the message is present only in polyps of the colony and missing in the larvae and primary polyps. A medusa-specific gene was identified by screening a ZAPII cDNA library with a mAb specific for the striated muscle of the medusa. From a positive clone a gene fragment was isolated, sequenced and identified to encode the myosin heavy-chain protein of striated muscle. To find regulatory genes which are expressed specifically in only one of the life stages a homeobox gene most similar to the Hox 1 family of vertebrate homeobox genes respectively the cnox-1 homeobox gene of Hydra was isolated by PCR out of a cDNA pool prepared from RNA from striated muscle tissue of medusae. The expression pattern of the Hox-1-like gene was medusa-specific and preliminary data indicated a role of the gene product (a transcription factor) in the formation of striated muscle.