S5.5 Jan. 5 Redox signaling and the transition from basal metazoans to bilaterians BLACKSTONE, N.W.; Northern Illinois University email@example.com
Living things invariably consist of some kind of compartmentalized redox chemistry. Signaling pathways mediated by oxidation and reduction thus derive from the nature of life itself. The role of such redox signaling broadened with major transitions in the history of life. Prokaryotes often use redox signals to deploy one or more variant electron carriers and associated enzymes to better utilize environmental energy sources. Eukaryotes transcend the strong surface-to-volume constraints inherent in prokaryotic cells by moving chemiosmotic membranes internally. As a consequence, eukaryotic redox signaling is frequently between these organelle membranes and the nucleus, thus potentially involving levels-of-selection synergies and antagonisms. Multicellular eukaryotes typically exhibit redox gradients between layers of cells, due for instance to differences in the availability of substrate and oxygen. The origin of the animal mouth allowed sequestering large amounts of substrate, exaggerating these redox gradients. Multicellular redox regulatorsócollections of metabolically active cells emitting a disproportionate share of redox signalsócorrespond to these steep redox gradients. In early-branching metazoans such as cnidarians and sponges, environmentally based redox signals actually or potentially mediate many aspects of growth, form, and life history. The origin of the bilaterians contradicts this trend of an increasing role for redox signaling in the history of life. Many bilaterians lost their ability to respond to redox signals because of the restricted potency of their somatic cells. Growth, development, and even senescence became more subject to internal signals. Redox signaling was largely confined to the timing of life history. These changes may reflect the advantages of diminished levels-of-selection conflicts between the cell and the organism. In parallel, organism-level selection is more potent in bilaterians.