Abstract
As global warming progresses, heat and hypoxia are gradually becoming important factors threatening the survival, reproduction, and development of marine organisms. To determine the effect of heat and hypoxia on Apostichopus japonicus, whole genome methylation of the respiratory tree was determined under heat, hypoxia, and heat-hypoxia conditions [designed as heat stress treatment (HT), hypoxia treatment (LO), and heat-hypoxia combined treatment (HL) groups]. The number of differentially methylated regions (DMRs) under three treatments was determined based on the Venn diagram. The network of the DMRs associated with promoters that were co-existed under the three conditions showed that circadian rhythm was involved based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Circadian rhythm-related genes, CRY1a, CRY1b, CLC, and TIM, decreased in LO and HL groups, while CRY1a, CRY1b, and BMAL1 increased in the HT group. Bisulfite sequencing PCR (BSP) showed that the methylation levels of CpG island regions in the promoters of CRY1a and CRY1b were upregulated in HT, LO, and HL groups, leading to the decreased promoter activity of CRY1a and CRY1b. RNAi of CRY1a and CRY1b led to increased enzyme activities of two energy-related enzymes, pyruvate kinase (PK) catalyzing the rate-limiting step in glycolysis, and ATPase hydrolyzing ATP to ADP, which were also increased under the three tested conditions. Thus, it was concluded that A. japonicus may respond to the heat, hypoxia, and heat-hypoxia stresses via the DNA methylation of heat, hypoxia, and heat-hypoxia stresses via the DNA methylation of CpG islands of circadian rhythm-related genes, which increased the activity of energy-related enzymes.
Highlights
Heat stress is a negative factor affecting the production and health of cultured animals, endangering the development of animal husbandry, causing serious economic losses and its impacts have been deteriorated due to global warming (St-Pierre et al, 2003; Quinteiro-Filho et al, 2010)
26◦C was used for heat stress and 2 mg/L dissolved oxygen (DO) was used for hypoxia stress, for the fact that the A. japonicus experienced the limits of temperature at 26◦C and 2 mg/L DO in summer in its important local living environment of northern Yellow sea and Bohai sea, as well as the definition of hypoxia by the committee on Environment and Natural Resources at the National Science and Technology Council in 2000 (Huang et al, 2012; Liu et al, 2014; Huo et al, 2019)
When the A. japonicus was reared in seawater in the groups of heat stress treatment (HT), hypoxia treatment (LO), and heat-hypoxia combined treatment (HL), the morphology of the respiratory tree changed dramatically
Summary
Heat stress is a negative factor affecting the production and health of cultured animals, endangering the development of animal husbandry, causing serious economic losses and its impacts have been deteriorated due to global warming (St-Pierre et al, 2003; Quinteiro-Filho et al, 2010). Heat acclimation is regulated by epigenetic factors from previous work, such as DNA methylation and histone methylation (Horowitz, 2016). Previous researches have shown that the DNA methylation profiles changed under heat stress (Horowitz, 2016). DNA methyltransferases (DNMTs), such as DNMT1 and DNMT3, have been proven in response to heat stress before the formation of heat acclimation, indicating a relationship between methylation modification and heat stress (Dai et al, 2017, 2018). The pieces of evidence have shown that changes of CpG methylation profile in HSP70 distal promoter region in the chicken and high mitochondrial calcium content in Rattus norvegicus may respond to heat acclimation (Assayag et al, 2012; Kisliouk et al, 2017). DNA methylation can help organisms to adapt to environmental changes through different adjustment methods
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