Extraction And Identification Of Milk Derived Exosomes From Yak And Jersey Cattle-yak And Comparative Analysis Of MiRNA Expression Profiles

Yak(Bos grunniens)is an endemic cattle species that mainly lives in the alpine regions at an altitude of more than 3,000 m.It has a large number,wide distribution,and strong adaptability to the plateau environment.Yak milk yield is relatively low,but yak milk is rich in protein,fat,lactose,and minerals.Jersey cattle-yak is a hybrid generation of yak and Jersey cattle,its heterosis is obvious and economic benefit is significant.Studies have shown that a variety of biomolecules carried by milk derived exosomes play important roles in cell growth,development,immune regulation,and a variety of pathophysiological processes.Micro RNA(miRNA)is a small endogenous non-coding RNA with a length of about 18-25 nucleotides.Many studies have shown that miRNA plays an important role in mammary gland development and milk synthesis.At present,most studies focus on the expression profiles of milk derived exosomes miRNAs in yaks in different lactation period,while there are few studies on the comparison of milk derived exosomes miRNA expression profiles between different breeds.Therefore,in order to explore the difference of lactation performance between yak and Jersey cattle-yak,in this study,yak milk and Jersey cattle-yak milk were selected as the research objects,divided into 4 groups of test comparison analysis: P1:Jersey cattle-yak in June vs yak in June,P2: Jersey cattle-yak in June vs Jersey cattleyak in December,P3: Jersey cattle-yak in June vs yak in December,and P4: yak in June vs yak in December.Milk components was detected and compared by milk composition rapid analyzer.Density gradient centrifugation was used to extract milk-derived exosomes,and the expression profile was constructed by small RNA sequencing and bioinformatics analysis.To provide basic data for yak improvement using Jersey cattle.The main results are as follows:1.The results of milk composition comparison showed that in the P1 group,the casein,fat,total solids,non-fat solids,and lactose of yak milk in June were significantly higher than those of Jersey cattle-yak milk(P<0.01),and the freezing point was significantly lower than that of Jersey cattle-yak milk(P<0.01).In the P2 group,the casein,protein,total solids,and acidity of Jersey cattle-yak milk in June were significantly lower than those in December(P<0.01),the fat was significantly lower than that in December(P<0.05),and the lactose,citric acid and freezing point were significantly higher than those in December(P<0.01).In the P3 group,the citric acid of yak milk in December was significantly higher than that of Jersey cattle-yak milk(P<0.01),the non-fat solids were significantly higher than that of Jersey cattle-yak milk(P<0.05),and the freezing point was significantly lower than that of Jersey cattle-yak milk(P<0.01).In the P4 group,the protein and acidity of yak milk in June were significantly lower than those in December(P<0.01),while the lactose was significantly higher than that in December(P<0.01).The results of correlation analysis between milk composition indexes showed that casein was positively correlated with protein,fat and total solids,protein was positively correlated with total solids and nonfat solids,and lactose was negatively correlated with casein,protein,fat,total solids,and non-fat solids.2.The particle size of yak milk derived exosomes was larger than that of Jersey cattle-yak,and the concentration was higher than that of Jersey cattle-yak.The particle size of milk derived exosomes extracted in June was smaller than that extracted in December,and the concentration was higher than that extracted in December.The miRNA expression profiles of milk derived exosomes from yak and Jersey cattle-yak were constructed by miRNA sequencing.Twenty-two,120,78 and 62 differentially expressed miRNAs(DEMs)were identified in P1-P4 groups,respectively.The four groups of DEMs target genes were enriched in extracellular exosomes,cytoplasm,endoplasmic reticulum,protein binding,axon guidance,MAPK signaling pathway and other functions and signaling pathways related to milk composition.The correlation between DEMs and milk composition was analyzed,and the four groups of DEMs were significantly correlated with lactose.