Expression profiling and functional characterization of the duplicated Oxr1b gene in zebrafish

Oxidation Resistance Gene 1 (OXR1) is a conserved gene family involved in protecting various species against oxidative stress. The zebrafish expresses a pair of OXR1 paralogs (i.e., oxr1a and oxr1b). Our previous work has revealed the importance of oxr1a in regulating antioxidant defenses during oxidative stress, but the role of oxr1b is remains unknown. Herein we reported the spatial-temporal expression of oxr1b and revealed its function through reverse genetics. The results showed that, as with oxr1a, oxr1b is a typical maternal-zygotic gene. Its mRNA is mainly distributed in the eye, brain and nervous system (e.g., anterior/posterior lateral line ganglion, neuromasts and spinal cord neuron). Although oxr1a and oxr1b genes have similar expression patterns during embryonic development, the latter have higher levels at the corresponding stages. Subsequently, a viable oxr1b^-/- mutant was generated by the CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated protein 9) system. Oxr1b knockout caused multiple antioxidant genes (i.e., gpx4a, gpx4b, sod1 and sod3b) to be downregulated, resulting in hypersensitive to oxidative stress. Furthermore, by comparative transcriptome analysis, we found that oxr1b knockout inhibits multiple signal transduction pathways (e.g., MAPK signaling pathway, calcium signaling pathway, cAMP signaling pathway and ErbB signaling pathway) during oxidative stress, thereby suppressing early stress response and ultimately impairing the anti-apoptosis pathway. In conclusion, our findings demonstrate that the duplicated oxr1b gene has an important role in regulating the antioxidant defenses by modulating signaling transduction and early stress response during oxidative stress.