CLONING OF A RAS-RELATED GENE FROM HYDRA WHICH RESPONDS TO HEAD-SPECIFIC SIGNALS

Members of the Ras family of proteins are important components of sign al transduction pathways responding to external signals and leading to changes in cell behavior. Analysis of two sns-related genes in the ph ylogenetically old metazoan Hydra indicates that in normal animals bot h genes are expressed in all body regions of the polyp. Upon head remo val, however, the transcript level of one of the two genes, ras2, decr eases rapidly in the upper gastric region which is adjacent to the for mer head. The decrease is transient and specific for ras2, since no ch anges could be observed in the transcript level of the related ras1 ge ne or any other gene. The disappearance of the ras2 mRNA can be preven ted completely by brief exposure of decapitated polyps to the protein kinase C activator TPA, which previously was shown to be capable of co nverting gastric tissue into head tissue [Muller, W.A. In: Othmer, H.G . (Ed.) Experimental and Theoretical Advances in Biological Pattern Fo rmation. Plenum Press, New York, NY, 1993, pp. 237-253]. The finding t hat Hydra ras2 expression is strongly dependent on a signal from the h ead provides the first evidence for ras expression being regulated in pattern formation.