A newly discovered oxidant defence system and its involvement in the development of Aurelia aurita (Scyphozoa, Cnidaria): reactive oxygen species and elemental iodine control medusa formation

Abstract

In Aurelia aurita, applied iodine induces medusa formation (strobilation). This process also occurs when the temperature is lowered. This was found to increase oxidative stress resulting in an increased production of iodine from iodide. One polyp produces several medusae (initially termed ephyrae) starting at the polyp's oral end. The spreading of strobilation down the body column is controlled by a feedback loop: ephyra anlagen decrease the tyrosine content in adjacent polyp tissue by producing melanin from tyrosine. Endogenous tyrosine is able to remove iodine by forming iodiferous tyrosine compounds. The reduced level of tyrosine causes the ephyra-polypborder to move towards the basal end of the former polyp. We argue that an oxidant defence system may exist which makes use of iodide and tyrosine. Like other marine invertebrates, polyps of Aurelia contain iodide ions. Inevitably produced peroxides oxidise iodide into iodine. The danger to be harmed by iodine is strongly decreased by endogenous tyrosine which reacts with iodine to form iodiferous tyrosine compounds including thyroxin. Both substances together, iodide and tyrosine, form an efficient oxidant defence system which shields the tissue against damage by reactive oxygen species. In the course of evolution (from a species at the basis of the animal kingdom like Aurelia to a highly evolved species like man) the waste product thyroxin (indicating a high metabolic rate) has developed into a hormone which controls the metabolic rate.

Compartments in Scyphozoa

“…In this ephyra the tentacles regress and a rhopalium forms in close proximity to some of these tentacles (Friedemann 1902). In natural samples and under certain treatments various transition stages between rhopalia and tentacles have been observed, indicating that rhopalia and tentacles are homologue organs (Thiel 1963;Berking et al 2005). Thus one can posit Note that only even numbers of pouches form.…”

Iodine accumulation in sea urchin larvae is dependent on peroxide

“…For example, iodine is essential for the synthesis of thyroid hormones (THs), a group of developmental and metabolic hormones that are produced in the vertebrate thyroid gland (Zoeller et al, 2007). Iodine also functions independently of THs, predominantly through its action as an inorganic antioxidant (Küpper et al, 2008;Aceves et al, 2005;Berking et al, 2005;Shrivastava et al, 2006). This element occurs in several oxidative states within aqueous environments.…”

“…Non-hormonal iodide acts as an antioxidant in Cnidarians (Aurelia aurita) and in Laminaria (Berking et al, 2005;Kupper et al, 2008), and hypothetically in mammalian physiology as well (Aceves et al, 2005;Shrivastava et al, 2006) (reviewed by Venturi and Venturi, 2009). With most reactive oxygen species (ROS), iodine is more reactive than other halogens such as bromide and chloride (Luther et al, 1995;Küpper et al, 2008).…”

Asexual reproduction of Nausithoe aurea (Cnidaria, Scyphozoa, Coronatae) induced by sterile polystyrene dishes

“…The cause is probably the formation of Reactive Oxygen Species (ROS) by substances that were used to turn the polystyrene dishes sterile, as pointed out by Herrmann et al (2003) and Berking et al (2005).…”

“…Berking et al (2005) showed that the addition of 1nM of Hydrogen Peroxide (H 2 O 2 ) causes in A. aurita up to 50% of strobilation. Nevertheless, high concentrations of H 2 O 2 can result in cell injuries observed as DNA damages, disabling dehydrogenases (Spragg et al, 1987).…”