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 signal transduction pathways responding to external signals and leading to changes in cell behavior. Analysis of two ras-related genes in the phylogenetically old metazoan Hydra indicates that in normal animals both genes are expressed in all body regions of the polyp. Upon head removal, however, the transcript level of one of the two genes, ras2, decreases rapidly in the upper gastric region which is adjacent to the former head. The decrease is transient and specific for ras2, since no changes could be observed in the transcript level of the related ras1 gene or any other gene. The disappearance of the ras2 mRNA can be prevented completely by brief exposure of decapitated polyps to the protein kinase C activator TPA, which previously was shown to be capable of converting gastric tissue into head tissue [Müller, W.A. In: Othmer, H.G. (Ed.) Experimental and Theoretical Advances in Biological Pattern Formation. Plenum Press, New York, NY, 1993, pp. 237-253]. The finding that Hydra ras2 expression is strongly dependent on a signal from the head provides the first evidence for ras expression being regulated in pattern formation.