Comparison of the Transcriptome of the Ovine Mammary Gland in Lactating and Non-lactating Small-Tailed Han Sheep

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.

Comparative Transcriptome Analysis of Milk Somatic Cells During Lactation Between Two Intensively Reared Dairy Sheep Breeds

“…Ribosomal proteins are commonly found among the highly expressed genes in the mammary gland. In sheep, Wang et al (2020) found that ribosomal protein S29 ( RPS29) is highly expressed in both lactating and non-lactating sheep, while Paten et al (2015) found that ribosomal protein genes are highly expressed during late pregnancy compared to early lactation. Ribosomal protein genes have also been identified as DEGs elsewhere; in cattle many ribosomal protein genes were downregulated in cows with high milk protein and fat percentage ( Cui et al, 2014 ) and members of this gene family were found to be overexpressed in ewes uninfected from Mycoplasma agalactiae ( Chopra-Dewasthaly et al, 2017 ).…”

“…In sheep, many studies focus on sequencing the transcriptome of muscles ( Zhang et al, 2014 ), adipose tissues ( Wang et al, 2014 ), or skin ( Yao et al, 2019 ) and results are exploited as candidate markers in breeding schemes, toward the desired phenotype. Recently though, transcriptome sequencing in sheep targets mainly the mammary gland and in particular, the discovery of highly or differentially expressed genes among breeds or time-points of lactation ( Paten et al, 2015 ; Suárez-Vega et al, 2015 , 2017a ; Hao et al, 2019 ; Farhadian et al, 2020 ; Wang et al, 2020 ). Although these studies have explored the expression profile of sheep’s mammary gland during different stages of lactation, little is known about the underlying mechanisms that render the mammary gland highly productive or not within breed in terms of milk yield.…”

Identification of regulatory networks and hub genes controlling mammary gland development and lactation in dairy goats during the late lactation, dry period, and late gestation stages

“…The expression patterns of these genes found in this study were consistent with those of previous studies. [26,27], and their high expression levels may be closely related to milk synthesis during the LL and LG stages. FGF2 and FGF11, as members of the broblast growth factor family, exhibited similar expression patterns, and their expression levels were lower in the LL stage than in the DP and LG stages.…”

Effects Study of Early Weaning Time on the Growth and Development of Dairy Sheep Lamb

“…So it will be a nice female parent for Chinese dairy sheep breeding. However, the average milk yield (0.645 L/day) of STH ewes is lower then Katahdin (1.38 L/day) and Saint Croix (1.26 L/day) ewes with multiple-born lambs [9]. The DairyMeade (DM) sheep which derived from New Zealand, with high milk yield, is a suitable male parent for Chinese dairy sheep breeding.…”