Abstract
This study presents a dynamic characterization of the sheep milk transcriptome aiming at achieving a better understanding of the sheep lactating mammary gland. Transcriptome sequencing (RNA-seq) was performed on total RNA extracted from milk somatic cells from ewes on days 10, 50, 120 and 150 after lambing. The experiment was performed in Spanish Churra and Assaf breeds, which differ in their milk production traits. Nearly 67% of the annotated genes in the reference genome (Oar_v3.1) were expressed in ovine milk somatic cells. For the two breeds and across the four lactation stages studied, the most highly expressed genes encoded caseins and whey proteins. We detected 573 differentially expressed genes (DEGs) across lactation points, with the largest differences being found, between day 10 and day 150. Upregulated GO terms at late lactation stages were linked mainly to developmental processes linked to extracellular matrix remodeling. A total of 256 annotated DEGs were detected in the Assaf and Churra comparison. Some genes selectively upregulated in the Churra breed grouped under the endopeptidase and channel activity GO terms. These genes could be related to the higher cheese yield of this breed. Overall, this study provides the first integrated overview on sheep milk gene expression.
Highlights
Lactation is a specific mammalian function essential for newborn feeding
The analysis of milk somatic cells (MSCs) is a more accessible method compared to invasive approaches, especially when dynamic studies with several sampling timepoints are required for the same animal[8]
The successful isolation and generation of global gene expression data from ovine MSCs is reported for the first time
Summary
Lactation is a specific mammalian function essential for newborn feeding. The milk transcriptome has been characterized in various mammalian species[1,2,3]. Various RNA sources have been used to study the mammary gland transcriptome during lactation in mammals, including mammary gland biopsies[3], milk fat globules[1] and milk somatic cells (MSCs)[2]. The aim of this research was to gain a better understanding of the sheep lactating mammary gland and to compare the mammary gland transcriptome of two sheep breeds with different dairy production characteristics, Spanish Churra and Assaf. We performed RNA-seq analysis of MSCs in these two dairy sheep breeds at four different lactation time points with the aim of characterizing the expression pattern of the principal stages of lactation. The dynamic characterization of milk sheep expression profile and differences between the milk transcriptomes of Assaf and Churra breeds are described. The results described provide a significant advance in our knowledge of sheep lactating mammary gland gene expression and valuable information for future studies
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