The Internal Self-regulatory Rules Inside The Mammary Gland Of Chinese Holstein Cow During Lactation Cycle

The molecular events underneath the lactation curve of dairy animals had long been a biological conundrum for mammary biologists,as well as a cause of considerable lost income for dairy farmers.To better understand the self-regulatory insights and the developmental processes inside the mammary gland during lactation cycle,the whole-genome transcriptome profiles of bovine mammary epithelium from non-pregnant cows at five different lactation stages were investigated using RNA-seq technique.RNA-seq enables analysis of the complexity of whole eukaryotic transcriptomes with less bias,greater dynamic range,lower frequency of false-positive signals,and higher reproducibility,have become a comprehensive and accurate tool for gene expression pattern analyses.In total,we obtained 37.98 gigabytes(Gb)reads in length with 86.34–88.24%of uniquely aligned reads for the five samples.The differentially expressed genes were identified by comparing the gene expression pattern of different lactation stage combinations.Integrated analysis of differential gene expression and previously reported QTL,Gene Ontology and pathway analysis,protein-protein interaction(PPI)analysis were implied in this study.Furthermore,qRT-PCR and immunohistochemistry technology were also carried out to validate the repeatability of data obtained by RNA-seq and the credibility of upward analysis.As a result,gene expression validation using qRT-PCR indicated high correlation(R~2=0.866);Some differentially expressed genes were found to be candidate genes or locate in the known quantitative trait loci regions that are associated with multiple milk production traits;Proteins of four potentially important genes were confirmed to be expressing in mammary epithelium of dairy cows.Integrated analysis of differential gene expression indicated internal self-regulatory rules of mammary gland underneath the shape of milk production curve.Firstly,mammary gland during lactation onset and involution is enriched into similar activities,but with opposite regulatory directions.Secondly,extracellular matrix(ECM)remodeling were abundantly involved in the lactation stages before and after peak milk,however,with opposite regulatory directions.The discoveries in the study will provide crucial information to improve milk production performance of dairy cows.