Stepwise Transfer from High to Low Lithium Concentrations Increases the Head-Forming Potential in Hydra vulgaris and Possibly Activates the PI Cycle

Abstract

Lithium ions affect pattern formation in the freshwater polyp Hydra vulgaris in a complex manner. Although a long-term treatment with 1 mM LiCl completely suppresses both head formation and budding, a reduction of the lithium concentration during a long-term treatment from 4 to 1 mM LiCl strongly promotes the differentiation of ectopic head structures. Meanwhile, budding, often interpreted as a special case of head formation, remains suppressed. The appearance of ectopic tentacles under these conditions is surprising as they develop while the animals remain in the presence of 1 mM LiCl, a concentration which would normally suppress the formation of tentacles. On a molecular level, the induction of ectopic head structures by the shift in the LiCl concentration is preceded by an increase in the level of inositol phosphates, indicating an activation of the phosphatidylinositol (PI) cycle. Increased inositol phosphate levels persist for at least 24 hr. Our results provide evidence that (i) tentacle- and bud-forming systems need different and possibly mutually exclusive physiological preconditions and (ii) prolonged inhibition of the PI cycle after initial activation might be necessary to obtain ectopic tentacles.

The level of expression of a protein kinase C gene may be an important component of the patterning process in Hydra

“…In these studies, activators of PI-PKC signalling like DAG or arachidonic acid induced head formation, whilst inhibitors, lithium and the non-physiological PKC activator TPA had very complex effects and resulted in suppression or induction of either structure. Concomitant with (ectopic) head formation, an activation of the PI-cycle was observed, which suggests activation of PKC as a component of head formation (Hassel and Bieller 1996). The work presented in this paper extends these observations.…”

“…Lithium ions have been shown to block signalling through the phosphatidylinositol pathway in various systems (for reviews see Berridge et al 1989;Manji and Lenox 1994), including Hydra (Hassel 1996;Hassel and Bieller 1996). Continuous treatment of Hydra polyps with a constant concentration of LiCl suppresses head formation and promotes ectopic foot formation on the body column (Hassel and Berking 1990;Hassel et al 1993).…”

Patterning a multi-headed mutant in Hydractinia: enhancement of head formation and its phenotypic normalization.

“…Another known inhibitor of GSK-3, lithium, evoked similar antagonistic responses in Hydra vulgaris. A particular pulse-type treatment induced the development of oversized heads and supernumerary tentacles, while long-term exposure to lithium caused the development of ectopic feet and suppressed the capacity to regenerate heads (Hassel and Berking, 1990;Hassel and Bieller, 1996).…”

Upregulation of a Hydra vulgaris cPKC gene is tightly coupled to the differentiation of head structures

“…Whilst interference with PI/PKC signalling suppresses head formation (Hassel et al 1993), ectopic head formation is correlated with activation of the PI cycle (Hassel and Bieller 1996). Moreover, PKC activating agents such as 1,2-dioctanoyl-snglycerol (DAG), alone or in combination with arachidonic acid (AA), induce ectopic head formation in intact polyps (Müller 1989;1995;Müller et al 1993), whilst a tumour promoting phorbol ester (12-O-tetradecanoylphorbol-13-acetate; TPA) induces both ectopic head and foot formation (Müller 1990).…”