Identification and characterization of circular RNAs in mammary gland tissue from sheep at peak lactation and during the non lactating 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 up-regulated 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.

Automated summary

Circular RNAs are a widespread class of noncoding RNA in eukaryote tissues, with some having clear biological functions. A study in sheep showed the expression profiles of circular RNAs in mammary gland tissue at peak lactation and nonlactating stages, confirming the expression and identity of multiple circular RNAs. In peak lactation, 40 up-regulated and 1 downregulated circular RNAs were identified, with parental genes related to various molecular functions. Furthermore, five differentially expressed circular RNAs were analyzed to predict their target microRNAs, revealing some microRNAs associated with mammary gland development.