Multicellular redox regulation: integrating organismal biology and redox chemistry

Catalyst-free Click PEGylation reveals substantial mitochondrial ATP synthase sub-unit alpha oxidation before and after fertilisation

Using non-reducing Western blotting to assess protein thiol redox state is challenging because most reduced and oxidised forms migrate at the same molecular weight and are, therefore, indistinguishable. While copper catalysed Click chemistry can be used to ligate a polyethylene glycol (PEG) moiety termed Click PEGylation to mass shift the reduced or oxidised form as desired, the potential for copper catalysed auto-oxidation is problematic. Here we define a catalyst-free trans-cyclooctene-methyltetrazine (TCO-Tz) inverse electron demand Diels Alder chemistry approach that affords rapid (k ~2000 M-1 s-1), selective and bio-orthogonal Click PEGylation. We used TCO-Tz Click PEGylation to investigate how fertilisation impacts reversible mitochondrial ATP synthase F1-Fo sub-unit alpha (ATP-α-F1) oxidation-an established molecular correlate of impaired enzyme activity-in Xenopus laevis. TCO-Tz Click PEGylation studies reveal substantial (~65%) reversible ATP-α-F1 oxidation at evolutionary conserved cysteine residues (i.e., C244 and C294) before and after fertilisation. A single thiol is, however, preferentially oxidised likely due to greater solvent exposure during the catalytic cycle. Selective reduction experiments show that: S-glutathionylation accounts for ~50-60% of the reversible oxidation observed, making it the dominant oxidative modification type. Intermolecular disulphide bonds may also contribute due to their relative stability. Substantial reversible ATP-α-F1 oxidation before and after fertilisation is biologically meaningful because it implies low mitochondrial F1-Fo ATP synthase activity. Catalyst-free TCO-Tz Click PEGylation is a valuable new tool to interrogate protein thiol redox state in health and disease.

What makes the cell differentiate?

In the present paper, I propose a hypothesis whereby the necessity to maintain the permanent energy-dissipating metabolic flux represents the primary force that determines the eukaryotic cell's choice to grow, divide and/or differentiate. This view is based on the universal structure and the strict redox neutrality of the core metabolic network. I propose that the direct substrate level coupling between metabolism and gene expression through epigenetic mechanisms provides a mechanistic explanation of how this control is implemented.

Mitochondria and the redox control of development in cnidarians

Mitochondria are the product of an ancient symbiosis between bacteria and host cells. While mitochondria function primarily in energy conversion, increasing amounts of evidence indicate that mitochondrial metabolic state can influence various emergent features of eukaryotic cells. Important intermediaries in such redox signaling include by-products of metabolism, particularly reactive oxygen species (ROS). This review uses cnidarians, a group of basally branching animals, to illustrate the many and varied effects of ROS on development. ROS from both mitochondria and algal symbionts are considered. Because some applications of ROS may lack specificity, the signaling demands of mitochondria and algae may to some extent conflict. An extensive algal symbiosis may thus be incompatible with a well-developed capacity for mitochondrial signaling.

Plasticity comparisons between plants and animals: Concepts and mechanisms

This review attempts to present an integrated update of the issue of comparisons of phenotypic plasticity between plants and animals by presenting the problem and its integrated solutions via a whole-organism perspective within an evolutionary framework. Plants and animals differ in two important aspects: mobility and longevity. These features can have important implications for plasticity, and plasticity may even have facilitated greater longevity in plants. Furthermore, somatic genetic mosaicism, intra-organismal selection, and genomic instability contribute to the maintenance of an adaptive phenotype that is especially relevant to long-lived plants. It is contended that a cross-kingdom phylogenetic examination of sensors, messengers and responses that constitute the plasticity repertoire would be more useful than dichotomizing the plant and animal kingdoms. Furthermore, physicochemical factors must be viewed cohesively in the signal reception and transduction pathways leading to plastic responses. Comparison of unitary versus modular organisms could also provide useful insights into the range of expected plastic responses. An integrated approach that combines evolutionary theory and evolutionary history with signal-response mechanisms will yield the most insights into phenotypic plasticity in all its forms.

Multicellular Redox Regulation in an Early‐Evolving Animal Treated with Glutathione

Redox signaling has emerged as a unifying theme in many seemingly disparate disciplines. Such signaling has been widely studied in bacteria and eukaryotic organelles and is often mediated by reactive oxygen species (ROS). In this context, reduced glutathione (GSH) acts as an important intracellular antioxidant, diminishing ROS and potentially affecting redox signaling. Complementing this cell-level perspective, colonial hydroids can be a useful model for understanding organism-level redox signaling. These simple, early-evolving animals consist of feeding polyps connected by tubelike stolons. Colonies treated exogenously with GSH or reduced glutathione ethyl ester (GEE) were expected to show a morphological change to sheetlike growth typical of low levels of ROS. Contrary to expectations, diminished stolon branching and polyp initiation was observed. Such runnerlike growth is associated with higher levels of ROS, and surprisingly, such higher levels were found in GSH- and GEE-treated colonies. Further investigations show that GSH triggered a feeding response in hydroid polyps, increasing oxygen uptake but at the same time relaxing mitochondrion-rich contractile regions at the base of polyps. Diminished gastrovascular flow and increased emissions of mitochondrial ROS also correlated with the observed runnerlike growth. In contrast to cell-level, "bottom-up" views of redox signaling, here the phenotype may arise from a "top-down" interaction of mitochondrion-rich regions and organism-level physiology. Such multicellular redox regulation may commonly occur in other animals as well.