Emerging Roles of Heat-Induced circRNAs Related to Lactogenesis in Lactating Sows

Analyses of circRNAs profiles of the lactating and nonlactating crops in pigeon (Columba livia)

Pigeon has the specific biological ability to produce pigeon milk (also known as crop milk) by its crop. Circular RNAs (circRNAs) are important noncoding RNAs acting as the sponges of miRNAs, but the molecular mechanism of circRNAs regulating crop milk production has not been reported in pigeon. We compared expression profiles of crops during lactating and nonlactating crops, and networks of competing endogenous RNAs (ceRNAs) were constructed. The results showed a total of 8,723 circRNAs were identified, and there were 770 differentially expressed circRNAs (DECs) between these two different periods of crops. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that the host genes of DECs were enriched in GnRH, MAPK, Insulin, Wnt, and AMPK signaling pathways. Furthermore, gga_circ_0000300 interacted with miR-92-2-5p, which targeted genes participating in lactation and milk composition synthesis. Gga_circ_0003018, gga_circ_0003019 and gga_circ_0003020 could bind with let-7c-5p regulating SOCS3 in crop milk production. These findings provide the circRNAs expression profiles and facilitate the analysis of molecular mechanism of crop milk production in pigeon.

CircEZH2 Regulates Milk Fat Metabolism through miR-378b Sponge Activity

Simple Summary

Heat stress has seriously threatened the performance and health of dairy cows and has become one of the most important factors restricting the development of the dairy industry. In our previous study, we found that heat stress markedly altered the expression patterns of circRNAs in dairy cow’s mammary gland tissue, and heat-induced circRNAs participated in the regulation of milk fat metabolism through competing endogenous RNA (ceRNA) networks. Therefore, we evaluated the roles of heat-induced circEZH2 in the regulation of milk fat metabolism in this study. In more detail, we found that circEZH2 affects the proliferation, apoptosis, and lipid metabolism of mammary gland epithelial cells, and successfully verified the targeting relationship of circEZH2-bta-miR378b-LPL and circEZH2-bta-miR378b-CD36. This experiment expands the basic data on the role of circRNA in milk fat regulation, and provides a theoretical basis for alleviating heat stress in dairy cows.

Abstract

In this study, we evaluated the roles of heat-induced circEZH2 in the regulation of milk fat metabolism. CircEZH2 overexpression increased HC11 cell proliferation and decreased apoptosis. These changes were accompanied by increased expression of proliferation marker proteins (PCNA, Cyclin D, and Cyclin E) and the anti-apoptotic protein Bcl2, while expression of the pro-apoptotic proteins Bax and cleaved-caspase was reduced. SiRNA-mediated silencing of EZH2 in HC11 cells had the opposite effects. CircEZH2 overexpression promoted the uptake of a fluorescent fatty acid (Bodipy) as well as expression of the fatty acid transport-related protein CD36, lipolysis-related protein LPL, and unsaturated fatty acid metabolism-related proteins FADS1 and SCD1. Dual luciferase reporter assays verified the targeting relationship of the two ceRNA networks, circEZH2-miR378b-LPL and circEZH2-miR378b-CD36. This information provides further clarification of the role of circRNAs in milk fat regulation in addition to a theoretical basis for alleviating the effects of heat stress on milk production by dairy cows.

Electronically controlled cooling pads can improve litter growth performance and indirect measures of milk production in heat-stressed lactating sows

Heat stress (HS) decreases lactation output in sows due to an attempt to reduce metabolic heat production. However, this negatively affects litter growth performance. Therefore, the study objective was to determine whether electronically controlled cooling pads (ECP) would improve indirect measures of lactation output (e.g., total heat production; THP) and litter growth performance in HS exposed sows. Over two repetitions, 12 multiparous (2.69 ± 0.85) lactating sows [265.4 ± 26.1 kg body weight (BW)] and litters were assigned to either an ECP (n = 3/repetition) or a non-functional ECP (NECP; n = 3/repetition) and placed into farrowing crates within indirect calorimeters from d 3.7 ± 0.5 to d 18.7 ± 0.5 of lactation. Litters were standardized across all sows (11.4 ± 0.7 piglets/litter), and sows were provided ad libitum feed and water. All sows were exposed to cyclical HS (28.27 ± 0.26°C nighttime to 33.09 ± 0.19°C daytime). On d 4, 8, 14, and 18 of lactation, indirect calorimetry was performed on each individual sow and litter to determine THP and THP/kg BW 0.75. Body temperature (TB) was measured hourly using vaginal implants, and respiration rate [RR; breaths per minute (bpm)] was measured daily at 0700, 1100, 1300, 1500, and 1900 hrs. Sow feed intake (FI) was assessed daily. Litter weights were obtained at birth, on d 4, 8, 14, and 18 of lactation, and at weaning. Data were analyzed using PROC GLIMMIX with sow and/or litter as the experimental unit. An overall decrease (P < 0.01; 25 bpm) in RR and maximum daily TB (P = 0.02; 0.40°C) was observed in ECP versus NECP sows. An increase in THP (P < 0.01; 20.4%) and THP/kg BW 0.75 (P < 0.01; 23.1%) was observed for ECP when compared to NECP sows and litters. Litter average daily gain and weaning weight was increased (P < 0.05; 25.0 and 19.2%, respectively) for ECP versus NECP litters. No FI differences were observed (P = 0.40) when comparing ECP (5.66 ± 0.31 kg/d) and NECP (5.28 ± 0.31 kg/d) sows. In summary, ECPs improve litter growth, thermoregulatory measures, and bioenergetic parameters associated with greater milk production in lactating sows exposed to cyclical HS.

Emerging roles of circRNAs in regulating thermal and hypoxic stresses in Apostichopus japonicus (Echinodermata: Holothuroidea)

Some sea cucumbers are economically and ecologically important, but they are threatened by thermal and hypoxic stress in changing oceanographic conditions. We construct circRNAs profiles, reveal circRNAs characters, and illustrate the potential regulatory roles of circRNAs in one commercially important species of sea cucumber, Apostichopus japonicus. Reads are distributed in intergenic (44.14%), exonic (48.26%) and intronic (7.60%) regions of the genome. A total of 1684 circRNAs were identified, and the most common spliced length is 269 nt in the present study. In three treatments (HT [thermal stress], LO [hypoxic stress], and HL [combined thermal and hypoxic stress]), 24, 27 and 27 differentially expressed (DE) circRNAs were identified, respectively. Five novel DE-circRNAs commonly occur in these treatments (novel_circ_0003311, novel_circ_0000229, novel_circ_0003944, novel_circ_0001458 and novel_circ_0000707), and based on them, potential circRNA-miRNA binding pairs were predicted. Sanger sequencing, RNase R treatment experiment and qPCR validation identified the accuracy of the circRNAs. Key circRNAs identified in the present study were covalently closed and were more stable under RNase R treatment than linear RNAs. Based on function analysis, circRNAs could regulate metabolic process, signal transduction, and ion responses in A. japonicus when exposed to thermal and hypoxic stress, and 'regulation of response to stimulus' is a common gene ontology (GO) term that is significantly enriched in each treatment; GO terms for 'DNA' and 'stress' are commonly enriched in heat-related treatments (HT and HL); and GO terms for 'protein' are commonly enriched in hypoxia-related treatments (LO and HL). When environmentally stressed, 'metabolism,' 'transport and catabolism,' 'membrane transport,' and 'signal transduction' were significantly responded in sea cucumber based on KEGG analysis. We provide insights into circRNA functions in stress regulation and lay a foundation for invertebrate circRNA research.

Functional Role of circRNAs in the Regulation of Fetal Development, Muscle Development, and Lactation in Livestock

circRNAs are a class of endogenous noncoding RNA molecules with closed loop structures. They are mainly responsible for regulating gene expression in eukaryotic cells. With the emergence of high-throughput RNA sequencing (RNA-Seq) and new types of bioinformatics tools, thousands of circRNAs have been discovered, making circRNA one of the research hotspots. Recent studies have shown that circRNAs play an important regulatory role in the growth, reproduction, and formation of livestock products. They can not only regulate mammalian fetal growth and development but also have important regulatory effects on livestock muscle development and lactation. In this review, we briefly introduce the putative biogenic pathways and regulatory functions of circRNA and highlight our understanding of circRNA and its latest advances in fetal development, muscle development, and lactation biogenesis as well as expression in livestock. This review will provide a theoretical basis for the research and development of related industries.

Genome-wide identification and functional prediction of circular RNAs in response to heat stress in Chinese Holstein cows

Heat stress (HS) leads to substantial economic loss of dairy industry each year. The negative effect of HS in dairy cows is becoming one of the more urgent issue due to accelerating side-effects of global warming. Various genes are involved in HS response but the information about the role of noncoding RNAs, especially circular RNAs (circRNAs) is largely unknown. In our study, we aimed to investigate the different expression profile of circRNAs between HS and Non-heat-stressed condition (NC) of Chinese Holstein cow's mammary gland. CircRNAs were identified using RNA sequencing and bioinformatics analysis. In total, 37405 circRNAs were detected and 95 were differentially expressed (DE), including 15 downregulated and 80 upregulated circRNAs in HS group compared to NC. Eight circRNAs were randomly selected to verify the RNA sequencing result. Further, Sanger sequencing validated the backsplicing site of the eight circRNAs. Moreover, results obtained from the Quantitative real time PCR (qRT-PCR) showed consistent expression trend with that of RNA sequencing. GO annotation and KEGG analysis suggested that these DE circRNAs probably involved in the energy metabolic regulation. Furthermore, we constructed ceRNA network and the result indicated that these DE circRNAs could regulate lactation through IGF1 and PRL signaling pathway.

MicroRNAs as Biomarkers for Animal Health and Welfare in Livestock

MicroRNAs (miRNAs) are small and highly conserved non-coding RNA molecules that orchestrate a wide range of biological processes through the post-transcriptional regulation of gene expression. An intriguing aspect in identifying these molecules as biomarkers is derived from their role in cell-to-cell communication, their active secretion from cells into the extracellular environment, their high stability in body fluids, and their ease of collection. All these features confer on miRNAs the potential to become a non-invasive tool to score animal welfare. There is growing interest in the importance of miRNAs as biomarkers for assessing the welfare of livestock during metabolic, environmental, and management stress, particularly in ruminants, pigs, and poultry. This review provides an overview of the current knowledge regarding the potential use of tissue and/or circulating miRNAs as biomarkers for the assessment of the health and welfare status in these livestock species.

Identification and characterization of circular RNAs in mammary gland tissue from sheep at peak lactation and during the nonlactating period

Circular RNAs are a class of noncoding RNA with a widespread occurrence in eukaryote tissues, and with some having been demonstrated to have clear biological function. In sheep, little is known about the role of circular RNAs in mammary gland tissue, and therefore an RNA sequencing approach was used to compare mammary gland tissue expression of circular RNAs in 9 Small Tail Han sheep at peak lactation, and subsequently when they were not lactating. These 9 sheep had their RNA pooled for analysis into 3 libraries from peak lactation and 3 from the nonlactating period. A total of 3,278 and 1,756 circular RNAs were identified in the peak lactation and nonlactating mammary gland tissues, respectively, and the expression and identity of 9 of them was confirmed using reverse transcriptase-polymerase chain reaction analysis and DNA sequencing. The type, chromosomal location and length of the circular RNAs identified were ascertained. Forty upregulated and one downregulated circular RNAs were characterized in the mammary gland tissue at peak lactation compared with the nonlactating mammary gland tissue. Gene ontology enrichment analysis revealed that the parental genes of these differentially expressed circular RNAs were related to molecular function, binding, protein binding, ATP binding, and ion binding. Five differentially expression circular RNAs were selected for further analysis to predict their target microRNAs, and some microRNAs reportedly associated with the development of the mammary gland were found in the constructed circular RNA-microRNA network. This study reveals the expression profiles and characterization of circular RNAs at 2 key stages of mammary gland activity, thereby providing an improved understanding of the roles of circular RNAs in the mammary gland of sheep.

Circular RNAs Are Regulators of Diverse Animal Transcriptomes: One Health Perspective

Derived from linear (parental) precursor mRNA, circRNA are recycled exons and introns whose ends are ligated. By titrating microRNAs and RNA binding proteins, circRNA interconnect networks of competing endogenous RNAs. Without altering chromosomal DNA, circRNA regulates skeletal muscle development and proliferation, lactation, ovulation, brain development, and responses to infections and metabolic stress. This review integrates emerging knowledge of circRNA activity coming from genome-wide characterizations in many clades of animals. circRNA research addresses one of the main pillars of the One Health vision – to improve the health and productivity of food animals and generate translational knowledge in animal species.

Circ09863 Regulates Unsaturated Fatty Acid Metabolism by Adsorbing miR-27a-3p in Bovine Mammary Epithelial Cells

Fatty acid composition plays a key role in regulating flavor and quality of milk. Therefore, in order to improve milk quality, it is particularly important to investigate regulatory mechanisms of milk fatty acid metabolism. Circular RNAs (circRNAs) regulate expression genes associated with several biological processes including fatty acid metabolism. In this study, high-throughput sequencing was used to detect differentially expressed genes in bovine mammary tissue at early lactation and peak lactation. Circ09863 profiles were influenced by the lactation stage. Functional studies in bovine mammary epithelial cells (BMECs) revealed that circ09863 promotes triglyceride (TAG) synthesis together with increased content of unsaturated fatty acids (C16:1 and C18:1). These results suggested that circ09863 is partly responsible for modulating fatty acid metabolism. Additionally, software prediction identified a miR-27a-3p binding site in the circ09863 sequence. Overexpression of miR-27a-3p in BMECs led to decreased TAG synthesis. However, overexpression of circ09863 (pcDNA-circ09863) in BMECs significantly reduced expression of miR-27a-3p and enhanced gene expression of fatty acid synthase (FASN), a target of miR-27a-3p. Overall, data suggest that circ09863 relieves the inhibitory effect of miR-27a-3p on FASN expression by binding miR-27a-3p and subsequently regulating TAG synthesis and fatty acid composition. Together, these mechanisms provide new research avenues and theoretical bases to improve milk quality.