Abstract
Small-Tailed Han (STH) sheep are known for their high fecundity, but the survival of lambs is compromised and influences the commercial return from farming these sheep, with this being attributed in part to starvation from insufficient milk production by the ewes. In this study, the transcriptome profiles of the mammary gland of lactating and non-lactating STH ewes were investigated using paired-end RNA sequencing (RNA-Seq). An average of 14,447 genes were found to be expressed at peak-lactation in the STH sheep, while 15,146 genes were expressed in non-lactating ewes. A total of 4,003 differentially expressed genes (DEGs) were identified. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that the DEGs were associated with a wide range of cellular components, biological processes and metabolic pathways, including binding activities, signaling pathways, cellular structures, and immune responses. The most highly expressed genes at peak-lactation included CSN2, LGB, LALBA, CSN1S1, CSN1S2, and CSN3, and the 10 most highly expressed genes accounted for 61.37% of the total Reads Per Kilobase of transcript, per Million mapped reads (RPKM). The most highly expressed genes in the mammary gland of non-lactating ewes included IgG, THYMB4X, EEF1A1, IgA, and APOE, and the 10 most highly expressed genes accounted for only 12.97% of the total gene RPKM values. This suggests that the sheep mammary gland undergoes a substantial development in milk protein synthesis infrastructure and promotion of protein transportation during lactation.
Highlights
The mammary gland is a complex exocrine organ in mammals and during lactation is responsible for producing critical nutrition as milk for young offspring
Using a cut-off of >0.01 RPKM to define potentially meaningful expressed genes [see Mortazavi et al (2008)], we detected an average of 14,447 and 15,146 genes expressed in ovine mammary gland tissues during peak-lactation and in the non-lactating period, respectively, with 13,928 genes being expressed at both stages
A principal component analysis (PCA) analysis revealed that all of the six grouped samples were clustered into two distinct groups, which reflected their status as lactating/nonlactating ewes
Summary
The mammary gland is a complex exocrine organ in mammals and during lactation is responsible for producing critical nutrition as milk for young offspring. Despite only accounting for approximately one percent of the global milk production and being ranked fourth by species in 20131, sheep milk is considered by some people to be superior to cow and goat milk It is well known that milk yield and quality is controlled by both genetic and environment factors, so an in-depth knowledge of the biological mechanisms that control mammary gland development and lactation offers an opportunity to improve milk production. In this respect, attention has become focused on the genes that underpin lactation and where and when they are expressed. To date transcriptome studies of the mammary gland in livestock have mainly been focused on dairy cows (Bionaz et al, 2012; Wickramasinghe et al, 2012; Cui et al, 2014; Seo et al, 2016; Dai et al, 2018) and dairy goats (Lin et al, 2015; Shi et al, 2015; Crisà et al, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
