title: Transcriptional events co-regulated by hypoxia and cold stresses in Zebrafish larvae.
abstract: BACKGROUND
  Hypoxia and temperature stress are two major adverse environmental conditions often encountered by fishes. The interaction between hypoxia and temperature stresses has been well documented and oxygen is considered to be the limiting factor for the thermal tolerance of fish. Although both high and low temperature stresses can impair the cardiovascular function and the cross-resistance between hypoxia and heat stress has been found, it is not clear whether hypoxia acclimation can protect fish from cold injury.
  
  
  RESULTS
  Pre-acclimation of 96-hpf zebrafish larvae to mild hypoxia (5% O2) significantly improved their resistance to lethal hypoxia (2.5% O2) and increased the survival rate of zebrafish larvae after lethal cold (10°C) exposure. However, pre-acclimation of 96-hpf larvae to cold (18°C) decreased their tolerance to lethal hypoxia although their ability to endure lethal cold increased. RNA-seq analysis identified 132 up-regulated and 41 down-regulated genes upon mild hypoxia exposure. Gene ontology enrichment analyses revealed that genes up-regulated by hypoxia are primarily involved in oxygen transport, oxidation-reduction process, hemoglobin biosynthetic process, erythrocyte development and cellular iron ion homeostasis. Hypoxia-inhibited genes are enriched in inorganic anion transport, sodium ion transport, very long-chain fatty acid biosynthetic process and cytidine deamination. A comparison with the dataset of cold-regulated gene expression identified 23 genes co-induced by hypoxia and cold and these genes are mainly associated with oxidation-reduction process, oxygen transport, hemopoiesis, hemoglobin biosynthetic process and cellular iron ion homeostasis. The alleviation of lipid peroxidation damage by both cold- and hypoxia-acclimation upon lethal cold stress suggests the association of these genes with cold resistance. Furthermore, the alternative promoter of hmbsb gene specifically activated by hypoxia and cold was identified and confirmed.
  
  
  CONCLUSIONS
  Acclimation responses to mild hypoxia and cold stress were found in zebrafish larvae and pre-acclimation to hypoxia significantly improved the tolerance of larvae to lethal cold stress. RNA-seq and bioinformatics analyses revealed the biological processes associated with hypoxia acclimation. Transcriptional events co-induced by hypoxia and cold may represent the molecular basis underlying the protection of hypoxia-acclimation against cold injury.
authors.affiliation: The Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, PR China. longyong@ihb.ac.cn.
authors.forename: Yong
authors.initials: Y
authors.lastname: Long
authors.affiliation: The Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, PR China. yjhzau@126.com.|University of the Chinese Academy of Sciences, Beijing, PR China. yjhzau@126.com.
authors.forename: Junjun
authors.initials: J
authors.lastname: Yan
authors.affiliation: The Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, PR China. guilisong@126.com.
authors.forename: Guili
authors.initials: G
authors.lastname: Song
authors.affiliation: The Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, PR China. lixiaohui353@163.com.|University of the Chinese Academy of Sciences, Beijing, PR China. lixiaohui353@163.com.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Li
authors.affiliation: The Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, PR China. 1135458539@qq.com.|University of the Chinese Academy of Sciences, Beijing, PR China. 1135458539@qq.com.
authors.forename: Xixi
authors.initials: X
authors.lastname: Li
authors.affiliation: The Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, PR China. qli@ihb.ac.cn.
authors.forename: Qing
authors.initials: Q
authors.lastname: Li
authors.affiliation: The Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei, PR China. zbcui@ihb.ac.cn.
authors.forename: Zongbin
authors.initials: Z
authors.lastname: Cui
mesh_terms: D000064:Acclimatization; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D058639:Cold-Shock Response / Q000235:genetics*; D020869:Gene Expression Profiling; D023281:Genomics; D000860:Hypoxia / Q000235:genetics*; D007814:Larva / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D015227:Lipid Peroxidation / Q000235:genetics; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D017423:Sequence Analysis, RNA; D016019:Survival Analysis; D014158:Transcription, Genetic; D015027:Zebrafish / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D029961:Zebrafish Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D029961:Zebrafish Proteins