Association Between Whole Blood Gene Expression And Lactation Function In Holstein Cows

Blood is an important source of nutrients for milk synthesis.Mammary epithelial cells absorb glucose,amino acid,fatty acid and other precursors from the blood through the transport carrier to synthesize milk.Plenty of blood is an important guarantee to maintain the metabolism of mammary substances and the normal function of lactation of dairy cows.The lactation process is completed with the participation of multiple tissues and organs of dairy cows.Blood can connect the scattered tissues and regulation of the whole body together.It is a kind of connective tissue that can ensure the communication between tissues and organs,and aggregating the molecular characteristics of the metabolic and transcriptional expression regulation system.The physiological and biochemical indexes of blood can quickly and objectively reflect the metabolism level and physiological health status of cows,which is an important index and diagnostic basis in cow feeding and management.Therefore,blood has the potential to study lactation performance of cows more directly and comprehensively.This study selects the blood of Holstein cows as the research object,using the RNA-Seq and GWAS method,from the high yield and low yield,different Angle of lactation stage and suffering from mastitis,comprehensive analysis of cow blood gene expression,SNP variation loci and expression regulation network characteristics,exploration and parsing cow blood gene expression associated with lactation function,screening key molecular markers affect lactation cows function,in order to improve the cow mammary initiative potential evaluation,increase the management decision-making and the safeguard lactation performance give full play to provide important scientific basis.The specific research results are as follows:1.By analyzing the whole blood gene expression profile of cows with high and low yield,100 differentially expressed genes were screened out,and 48 genes were located in the lactation related QTL region.Of the 100 differentially expressed genes,43 genes were highly expressed in high-yielding cows and 57 genes were highly expressed in low-yielding cows.High-expression genes in high-producing cows were significantly enriched in 14 KEGG signaling pathways(P<0.05),including the jak-stat signaling pathway,linoleic acid metabolism pathway,PPAR signaling pathway,toll-like receptor signaling pathway and other immune-related signaling pathways,which were significantly correlated with lactation performance of cows.By integrating the functions,selective signals and co-expression network analysis of the differentially expressed genes,24 candidate genes related to lactation function were selected,such as LPLt CPT1A,OLR1,IL13RA1,FHL1,ALOX12,CYP2J2 and BoLA-DQA1.2.Through the genetic basic research on lactation performance of cows,a total of 153 genome-wide significant SNPs sites were found,which were associated with a total of 15 traits such as lactation performance and immunity.Further gene annotation,QTL analysis and functional analysis were performed on these SNPs to screen out 26 important genes related to lactation performance,such as HCN1,HTR7,WNT5A,ACACB,EGFR,GRINA,TNFSF11 and FAT1.These genes were significantly enriched in important lactation related signaling pathways,including prolactin signaling pathway,insulin signaling pathway,breast development signaling pathway,Wnt signaling pathway,AMPK signaling pathway,substance metabolism pathway and immune response signaling pathway.3.Through the study on the lactation cycle of cows,it is found that there are complex gene expression regulation in the process of starting lactation(dry milk period vs.early lactation period)and ending lactation(late lactation period vs.dry milk period).During lactation initiation,2,922 differentially expressed genes were screened,and 2,578 differentially expressed genes were screened during the end of lactation,while the number of differentially expressed genes during lactation maintenance(early lactation-late lactation)was only 799.During lactation initiation,significantly upregulated differentially expressed genes are mainly involved in signaling pathways such as substance metabolism,positive regulation of catalytic activity,ribosomal synthesis,oocyte meiosis,oocyte maturation,and vesicular transport,which contribute to the formation and secretion of milk.It was found that up-regulated genes were down-regulated during the end of lactation.Dry milk period of cows,also the late pregnancy of cows,at this time the fetal growth and development is very fast,to consume a lot of nutrients,for the fetal growth and development needs.It was found that genes with high expression in dry milk stage were mainly involved in cell division,nucleic acid metabolism,embryonic organ development,nervous system development and metabolism,which were consistent with the characteristics of rapid growth and development of fetus in dry milk stage.Differential gene co-expression network analysis revealed the characteristic gene modules corresponding to different lactation stages,which provided an important gene set for studying the periodic changes of lactation of cows.Among them,the red gene module is highly correlated with the early lactation stage,and this module gene is mainly involved in the metabolic process of substances and regulates the start of lactation.4.Through the whole blood gene expression of dairy cows suffering from mastitis and healthy lactating cows,20 candidate genes for the study of resistance to mastitis in dairy cows were selected:GYG1,BoLA-DQA1,NT5DC2,AGAP3,SPAG1,MARCH9,LIMK2,POU2F2,TLR3,WIPI1,D2HGDH,FDXR,SPPL2B,ALOX5AP,CAPN10,CCDC191,CELSR3,PRAM1,CCDC88B and PRDX5,these genes will provide the basis for the research on the resistance genes of cow mastitis.Gene co-expression network analysis revealed that the gene regulation network of cows with mastitis was more complex,and two genes specific to the expression network were involved in different signaling pathways,maintaining the biological process under specific physiological conditions.In conclusion,this study applied genomics and transcriptome method to establish the relationship between the blood gene expression and lactation performance,explored the effects of differentially expressed genes in different stages of lactation on lactation performance of dairy cows,and selected the important genes might affect the function of lactation,which will increase breeding work for subsequent function verification and increase the breeding management initiative to provide important information.