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Dynamic profiles of the Yak mammary transcriptome during lactation

ABSTRACT: Dynamic transcriptome profiles in yak mammary gland were evaluated by sampling mammary tissue at -30, -15, 1, 15, 30, 60, 120, 180 and 240 d relative to parturition and using a bovine commercial microarray platform. Several bioinformatics tools were used to analyze the data, both as expression relative to -30 d and as expression relative to the previous time point. There were >6,000 differentially expressed transcript (DEG; FDR＜0.05; P＜0.05) throughout lactation with larger DEG observed at the onset (1 vs. -15d) and at the end of lactation (240 vs. 180d). Bioinformatics analysis allowed to identify lactation-related genes on yak chromosomes which laid the foundation for determination of QTL location. Among most-impacted bovine chromosomes (BTA), BTA6, BTA9 and BTA28 were induced while BTA3, BTA4 and BTA14 were inhibited throughout lactation. Functional analysis underlined an overall induction of lipid metabolism, suggesting increases in triglycerides synthesis likely regulated by PPAR signaling. Data suggested induction of amino acid metabolism while increasing secretion or protein, but decreasing proteasome, indicating a major role of amino acid handling and reduced protein degradation in the synthesis and secretion of milk proteins. Glycan biosynthesis, both for N-glycan and O-glycan, was induced suggesting increased glycan content in milk. Cell cycle and immune response, especially antigen processing and presentation, were strongly inhibited during lactation suggesting morphological changes were minimized while the mammary gland prevents immune hyper responses during lactation. Transcripts associated with response to radiation and low oxygen were enriched in the down-regulated DEG affected by stage of lactation. Except for the latter, functions affected by the transcriptomic adaptation to lactation in mammary tissue of yak were very similar to the ones observed in dairy cows.

ORGANISM(S): Bos taurus Bos grunniens

PROVIDER: GSE201438 | GEO | 2022/04/28

REPOSITORIES: GEO

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Project description:BACKGROUND: The lactating mammary gland responds to changes in milking frequency by modulating milk production. This response is locally regulated and, in dairy cows, the udder is particularly sensitive during early lactation. Relative to cows milked twice-daily throughout lactation, those milked four-times-daily for just the first 3 weeks of lactation produce more milk throughout that lactation. We hypothesized that the milk yield response would be associated with increased mammary cell turnover and changes in gene expression during frequent milking and persisting thereafter. Cows were assigned to unilateral frequent milking (UFM; left udder halves milked twice-daily; right udder halves milked four-times daily) on days 1 to 21 of lactation, followed by twice-daily milking for the remainder of lactation. Relative to udder halves milked twice-daily, those milked four-times produced more milk during UFM; the difference in milk yield declined acutely upon cessation of UFM after day 21, but remained significantly elevated thereafter. We obtained mammary biopsies from both udder halves on days 21, 23, and 40 of lactation. RESULTS: Mammary cell proliferation and apoptosis were not affected by milking frequency. We identified 75 genes that were differentially expressed between paired udder halves on day 21 but exhibited a reversal of differential expression on day 23. Among those genes, we identified four clusters characterized by similar temporal patterns of differential expression. Two clusters (11 genes) were positively correlated with changes in milk yield and were differentially expressed on day 21 of lactation only, indicating involvement in the initial milk yield response. Two other clusters (64 genes) were negatively correlated with changes in milk yield. Twenty-nine of the 75 genes were also differentially expressed on day 40 of lactation. CONCLUSIONS: Changes in milking frequency during early lactation did not alter mammary cell population dynamics, but were associated with coordinated changes in mammary expression of at least 75 genes. Twenty-nine of those genes were differentially expressed 19 days after cessation of treatment, implicating them in the persistent milk yield response. We conclude that we have identified a novel transcriptional signature that may mediate the adaptive response to changes in milking frequency.

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Dynamic profiles of the Yak mammary transcriptome during lactation

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