Abstract
Heat stress negatively influences milk production and disrupts normal physiological activity of lactating sows, but the precious mechanisms by which hyperthermia adversely affects milk synthesis in sows still remain for further study. Circular RNAs are a novel class of non-coding RNAs with regulatory functions in various physiological and pathological processes. The expression profiles and functions of circRNAs of sows in lactogenesis remain largely unknown. In the present study, long-term heat stress (HS) resulted in a greater concentration of serum HSP70, LDH, and IgG, as well as decreased levels of COR, SOD, and PRL. HS reduced the total solids, fat, and lactose of sow milk, and HS significantly depressed CSNαs1, CSNαs2, and CSNκ biosynthesis. Transcriptome sequencing of lactating porcine mammary glands identified 42 upregulated and 25 downregulated transcripts in HS vs. control. Functional annotation of these differentially-expressed transcripts revealed four heat-induced genes involved in lactation. Moreover, 29 upregulated and 21 downregulated circRNA candidates were found in response to HS. Forty-two positively correlated circRNA-mRNA expression patterns were constructed between the four lactogenic genes and differentially expressed circRNAs. Five circRNA-miRNA-mRNA post-transcriptional networks were identified involving genes in the HS response of lactating sows. In this study we establish a valuable resource for circRNA biology in sow lactation. Analysis of a circRNA-miRNA-mRNA network further uncovered a novel layer of post-transcriptional regulation that could be used to improve sow milk production.
Highlights
In seasonal climates, high ambient temperature is the primary environmental stress impacting domestic animal performance, including growth, reproduction, and lactation (Das et al, 2016)
Blood heat shock protein 70 (HSP70), lactate dehydrogenase (LDH), and immunoglobulin G (IgG) levels were significantly higher in the heat stress (HS) cohort compared with the non-heat stress (NS) group (P < 0.05)
Based on competing endogenous RNA (ceRNA) networks involved in mammopoiesis and lactogenesis under HS that we constructed, we identified a total of 10 interaction core genes (Figure S2)
Summary
High ambient temperature is the primary environmental stress impacting domestic animal performance, including growth, reproduction, and lactation (Das et al, 2016). In modern swine husbandry, lactating sows have been heavily selected for increased productivity (fertility, disease resistance, feed conversion efficiency, and so on) during the last two decades, and are especially at risk of HS (Renaudeau, 2005), as they have a thermal neutral zone between 16 and 22°C (Messias de Bragança et al, 1998). HS influences milk production in lactating sows, perhaps through an indirect effect associated with reduction in feed intake (Ribeiro et al, 2018); previous reports of Messias de Bragança et al (1998) and Silanikove et al (2009) suggested that there may be a direct effect of ambient temperature on mammary gland metabolism in connection with low milk yield. The ability to use powerful genomic tools to evaluate genetic differences associated with thermal tolerance can provide important information on the underlying mechanisms of HS on lactation, and will permit the selection of sows for resistance to HS
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