Transcriptome Analysis Of Breast Lipid Metabolism In The Lactation Cycle Of Chinese Holstein Cows

Cow lactation is a dynamic process.In this study,we have detected milk composition and milk fatty acid level in a complete lactation cycle of Chinese Holstein dairy cows.and then collected the mammary gland tissues at six specific time points of lactation to screen the differentially expressed genes by transcriptome sequencing and bioinformatics analysis.Finally,the genes related to the fatty acids metabolism were identified,and their expression patterns were further explored in combination with the changes of fatty acid.However,future works will be needed to explore the genes function related to fat and its regulatory mechanism in lactation cycle.The experiments were conducted at Experimental Ranch of Yangzhou University.Thirty healthy Chinese Holstein cows of parity of 2-3 were selected with the similar body condition and concentration of delivery period.Milk samples(100 mL)were collected to analyze milk composition and fatty acid composition at day 3,15,45,75,105,135,165,195,225,255,285,and 315 of milking.Three dairy cows with the similar body condition and delivery time was selected to collect mammary gland tissues using minimally invasive surgery at day 7 before delivery and day 30,90,180,270,and 315 of milking.Samples were then frozen in liquid nitrogen for RNA extraction and transcriptome analysis.The main results are as follows:1.Milk fat,protein,and non-fat milk had similar trend during the whole lactation period.The fat content was the highest at d7 and the lowest at d 195.The relative content of fat remained stable but decreased in the late lactation.The milk protein content was significantly higher than that of other sampling time(P<0.01),while there was no significant difference after 15 days(P>0.05).The relative content of non-fat milk solid was stable at d45-315,but there was no significant difference in lactation time between d45 and 315(P>0.05).The lactose content of non-fat milk was significantly higher than that of other sampling time The content of the relative content at d7 was the smallest,and remained relatively stable at d 15,but there were no obvious changes in the other stages of lactation.Through the milk fat in the four main components of fatty acids in the whole lactation cycle trends are classified,mainly divided into two categories of fatty acids:C14:0(myristic acid),C16:0(palmitic acid)fatty acids and C18:0(stearic acid),C18:1(oleic acid)fatty acids,and the trend of these two fatty acids tends to change in the lactation cycle It is speculated that the changes of myristic acid,palmitic acid and stearic acid and oleic acid in lipid metabolism of dairy cows may have different biological significance in different lactation stages.2.A total of 18 breast tissue samples were analyzed by transcriptome analysis.Seven days vs 30 days,30 days vs 90 days,90 days vs 180 days,180 days vs 270 days and 270 days were screened from all of the differentially expressed genes data.A total of 2144 up-regulated genes and 2042 down-regulated genes were identified by two different stages of differentially expressed genes.Two differentially expressed genes were compared with the 1460 transcripts expressing the lipid-related genes.From cross-analysis,a total of 413 lipid-related differential expression genes were obtained.Finally,the differences between the two successive and lipid-related up-regulated and down-regulated genes were analyzed by GO and KEGG enrichment.A total of 4466 GO term and 794 And then screened 248 GO term and 129 pathway-enriched pathways associated with lipid metabolism,and ultimately explained the differences in lipid metabolism between the two successive phase samples enriched on GO term and Pathway The relationship between genes and fatty acids.3.To calculate all the differences in lipid metabolism on GO term and Pathway in a lactation cycle,it showed that there were 185 important genes in the lactation cycle with lipid metabolism,which regulated milk fat metabolism in different lactation period.4.Through the dynamic clustering of lipid-related genes and GO enrichment analysis,five distinctly different(P<0.01)gene expression models were identified,from which the fifth gene cluster expression of the seven genes of LPIN1,ACSL1,CHPT1,ACSS2,AGPAT6,SCD and GPD1 are not only consistent with the expression of LPIN1,but also closely related to the regulation of fat metabolism in lactation.