LAUSR

Significance Reactive oxygen species (ROS) increase with age and have been shown to negatively impact age-related diseases. However, the physiological roles they might play in development have not been extensively characterized. Here, we show that ROS have essential functions as oocytes complete meiosis, the specialized cell division that generates haploid eggs, and transition to embryonic development. Meiotic progression and early embryonic divisions are defective when ROS is misregulated. Furthermore, we document the effects of ROS on specific proteins. Our identification of proteins altered in redox state as the oocyte transitions to an embryo provides a valuable resource to guide future exploration of ROS functions in early development. The regulatory system described here has important implications for female fertility. The metabolic and redox state changes during the transition from an arrested oocyte to a totipotent embryo remain uncharacterized. Here, we applied state-of-the-art, integrated methodologies to dissect these changes in Drosophila. We demonstrate that early embryos have a more oxidized state than mature oocytes. We identified specific alterations in reactive cysteines at a proteome-wide scale as a result of this metabolic and developmental transition. Consistent with a requirement for redox change, we demonstrate a role for the ovary-specific thioredoxin Deadhead (DHD). dhd-mutant oocytes are prematurely oxidized and exhibit meiotic defects. Epistatic analyses with redox regulators link dhd function to the distinctive redox-state balance set at the oocyte-to-embryo transition. Crucially, global thiol-redox profiling identified proteins whose cysteines became differentially modified in the absence of DHD. We validated these potential DHD substrates by recovering DHD-interaction partners using multiple approaches. One such target, NO66, is a conserved protein that genetically interacts with DHD, revealing parallel functions. As redox changes also have been observed in mammalian oocytes, we hypothesize a link between developmental control of this cell-cycle transition and regulation by metabolic cues. This link likely operates both by general redox state and by changes in the redox state of specific proteins. The redox proteome defined here is a valuable resource for future investigation of the mechanisms of redox-modulated control at the oocyte-to-embryo transition.