Hypoxia, a unique and essential environmental stress, evokes highly coordinated cellular responses, and hypoxia‐inducible factor (HIF) 1 in the hypoxia signaling pathway, an evolutionarily conserved cellular signaling pathway, acts as a master regulator of the transcriptional response to hypoxic stress. MicroRNAs (miRNAs), a major class of posttranscriptional gene expression regulators, also play pivotal roles in orchestrating hypoxia‐mediated cellular adaptations. Here, global miRNA expression profiling and quantitative real‐time PCR indicated that the up‐regulation of the miR‐462/miR‐731 cluster in zebrafish larvae is induced by hypoxia. It was further validated that miR‐462 and miR‐731 are upregulated in a Hif‐1α‐mediated manner under hypoxia and specifically target ddx5 and ppm1da , respectively. Overexpression of miR‐462 and miR‐731 represses cell proliferation through blocking cell cycle progress of DNA replication, and induces apoptosis. In situ detection revealed that the miR‐462/miR‐731 cluster is highly expressed in a consistent and ubiquitous manner throughout the early developmental stages. Additionally, the transcripts become restricted to the notochord, pharyngeal arch, liver, and gut regions from postfertiliztion d 3 to 5. These data highlight a previously unidentified role of the miR‐462/miR‐731 cluster as a crucial signaling mediator for hypoxia‐mediated cellular adaptations and provide some insights into the potential function of the cluster during embryonic development.—Huang, C.‐X., Chen, N., Wu, X.‐J., Huang, C.‐H., He, Y., Tang, R., Wang, W.‐M., Wang, H.‐L. The zebrafish miR‐462/miR‐731 cluster is induced under hypoxic stress via hypoxia‐inducible factor 1α and functions in cellular adaptations. FASEB J. 29, 4901–4913 (2015). www.fasebj.org

The present study was focused on physiology changes, innate immune responses, oxidative stress statuses in M. amblycephala treated with different oxygenation concentration and time, including control (dissolved oxygen, DO: 5.5 mg/L), 0.5 h acute hypoxia (DO: 3.5 and 1.0 mg/L respectively), 6 h comparable-acute hypoxia (DO: 3.5 mg/L) and then 24 h reoxygenation. The results revealed that hypoxia affected serum hemoglobin (Hb), methemoglobin (MetHb), glucose, Na+, succinatedehydrogenase (SDH), lactate acid (LD) and hepatic glycogen levels, which showed the increase except hepatic glycogen with the decrease of DO level. With the extension of hypoxia time, Hb, MetHb, glucose and LD were increased except Na+, SDH and hepatic glycogen levels, while all above investigated indexes were decreased after reoxygenation. With the decrease of DO level, interferon alpha (IFNα) and lysozyme (LYZ) were gradually increased, whereas albumin was decreased. However, albumin and LYZ levels were decreased after 6 h comparable-acute hypoxia, and remained at high levels after reoxygenation. On the other hand, the liver SOD and CAT, reactive species hydrogen peroxide (H2O2) and total ROS were all remained at lower levels under hypoxia. Finally, Hif-1α levels in liver, spleen and gill were increased with the decrease of DO level and prolongation of hypoxia time. The two Hsp70 isoforms were found in all detected tissues after hypoxia-reoxygenation treatment, whereas internal ribozyme entry site (IRES)-mediated junior Hsp70 was only detected in liver, spleen and gill. Taken together, these results suggest that hypoxia affect M. amblycephala physiology, immune and liver oxidative stress levels.