THE POLYP AND ITS MEDUSA - A MOLECULAR APPROACH

In the metagenic life cycle of hydroidans, the sexual stage, the medus a 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 anal yze 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. ars with the RNA fingerprinting techni que, 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 resu lts are compared with observations made earlier at the protein level. A gene specifically expressed in polyps is represented by the Pol-l cD NA. This cDNA was obtained from a differential screening of a cDNA lib rary for life stage specific genes and further characterized. The dedu ced amino acid sequence of Pol-l 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 lar vae and primary polyps. A medusa-specific gene was identified by scree ning a ZAPII cDNA library with a mAb specific for the striated muscle of the medusa. From a positive clone a gene fragment was isolated, seq uenced and identified to encode the myosin heavy-chain protein of stri ated muscle. To find regulatory genes which are expressed specifically in only one of the life stages a homeobox gene most similar to the Ho xl family of vertebrate homeobox genes respectively the cnox-1 homeobo x gene of Hydra a 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 indicate d a role of the gene product (a transcription factor) in the formation of striated muscle.