A major issue in regenerative medicine is the role of injury in promoting cell plasticity. Here we explore the function of reactive oxygen species (ROS) induced through lesions in adult zebrafish. We show that ROS production, following adult fin amputation, is tightly regulated in time and space for at least 24 hours, whereas ROS production remains transient (2 hours) in mere wound healing. In regenerative tissue, ROS signaling triggers two distinct parallel pathways: one pathway is responsible for apoptosis, and the other pathway is responsible for JNK activation. Both events are involved in the compensatory proliferation of stump epidermal cells and are necessary for the progression of regeneration. Both events impact the Wnt, SDF1 and IGF pathways, while apoptosis only impacts progenitor marker expression. These results implicate oxidative stress in regeneration and provide new insights into the differences between healing and regeneration.

Reactive oxygen species (ROS), which were originally classified as exclusively deleterious compounds, have gained increasing interest in the recent years given their action as bona fide signalling molecules. The main target of ROS action is the reversible oxidation of cysteines, leading to the formation of disulfide bonds, which modulate protein conformation and activity. ROS, endowed with signalling properties, are mainly produced by NADPH oxidases (NOXs) at the plasma membrane, but their action also involves a complex machinery of multiple redox-sensitive protein families that differ in their subcellular localization and their activity. Given that the levels and distribution of ROS are highly dynamic, in part due to their limited stability, the development of various fluorescent ROS sensors, some of which are quantitative (ratiometric), represents a clear breakthrough in the field and have been adapted to both ex vivo and in vivo applications. The physiological implication of ROS signalling will be presented mainly in the frame of morphogenetic processes, embryogenesis, regeneration, and stem cell differentiation. Gain and loss of function, as well as pharmacological strategies, have demonstrated the wide but specific requirement of ROS signalling at multiple stages of these processes and its intricate relationship with other well-known signalling pathways.

Aims: Recent advances in redox biology have emphasized the role of hydrogen peroxide (H ₂ O ₂ ) in the modulation of signaling pathways and revealed that H ₂ O ₂ plays a role in cellular remodeling in adults. Thus, an understanding of the mechanisms that control H ₂ O ₂ levels in mature tissue would be of great interest. Results: We used a denervation strategy to demonstrate that sensory neurons are responsible for controlling H ₂ O ₂ levels under normal conditions and after being lesioned. Moreover, we demonstrate that severed nerves respond to appendage amputation via the induction of Hedgehog signaling and that this signaling is responsible for H ₂ O ₂ production in the wounded epidermis. Finally, we show that H ₂ O ₂ and nerve growth are regulated via reciprocal action in adults. Innovation and Conclusion: These data support a new paradigm for the regulation of tissue homeostasis: H ₂ O ₂ attracts nerves and nerves control H ₂ O ₂ levels in a positive feedback loop. This finding suggests that the peripheral nerve redox environment could be a target for manipulating cell plasticity in adults. Antioxid. Redox Signal. 24, 299–311.

We implemented a noninvasive optical method for the fast control of Cre recombinase in single cells of a live zebrafish embryo. Optical uncaging of the caged precursor of a nonendogeneous steroid by one- or two-photon illumination was used to restore Cre activity of the CreER ^T2 fusion protein in specific target cells. This method labels single cells irreversibly by inducing recombination in an appropriate reporter transgenic animal and thereby can achieve high spatiotemporal resolution in the control of gene expression. This technique could be used more generally to investigate important physiological processes (e.g., in embryogenesis, organ regeneration, or carcinogenesis) with high spatiotemporal resolution (single cell and 10-min scales).