Milk Fat Synthesis Related Proteins And Their MRNA Expression In Yak(Bos Grunniens) Breast Tissue

High milk fat rate is a distinctive feature of yak milk.In breast tissue,fatty acids required for milk fat synthesis can be taken directly from the blood or synthesized de novo from breast tissue.In order to understand the main pathways,mechanisms and characteristics of milk fat synthesis in yak mammary gland tissues,yak mammary gland tissues at the resting stage,developmental stage,lactation peak period,late lactation period and milk lactation mammary gland tissue samples were collected as controls during lactation period.Based on morphological observations,real-time fluorescent quantitative PCR,immunoblotting and immunohistochemistry were used to detect lipoprotein lipase(LPL),fatty acid translocase(CD36)and acetyl-coenzyme at different developmental stages A carboxylase ?(Acetyl-CoA carboxylase alpha,ACC?),fatty acid synthase(Fatty acid synthase,FASN),stearoyl-CoA dehydrogenase 1(Stearoyl-CoA dehydrogenase 1,SCD1)and other fatty acid transport and synthesis related Changes in protein and mRNA expression.1.The acinar of the yak mammary gland tissue in the resting period is clustered,and a large number of adipocytes and connective tissue exist between the leaflets.During pregnancy,the mammary gland begins to develop until the peak lactation period and the late lactation period.The development process is accompanied by a decrease in fat cells and connective tissue,and the acinar is pulled from the mass into a network.In the process of lactation,there may be alternate lactation patterns in the acinus.At the same time,there was no difference between the breast tissue of lactating cows and that of yaks.2.The location of milk fat synthesis-related proteins in yak mammary gland tissue is almost universally found in mammary epithelial cells and ductal epithelial cells.The difference is that although FASN is visible in yak ductal epithelial cells,it is almost not found in ductal epithelial cells of dairy cows.expression.3.The expression of milk fat synthesis-related proteins at the mRNA level differs in yak mammary gland tissue at different periods.The LPL and CD36 genes were significantly higher in the late lactation period than in the peak lactation period(P <0.01),and the expression level was in an upward trend with the development of the mammary gland and the progress of lactation.The expression of FASN in quiescent breast tissue is significantly higher than that in other periods(P <0.01),and there is no significant difference between the expression levels during development,lactation and late lactation(P> 0.05).ACACA slowly rises from the resting period to the developmental period(P> 0.05),the expression of the lactation peak period is significantly lower than that of the late lactation period(P <0.01),the expression of SCD1 in the lactation peak period is significantly higher than that of the breast tissues With the progress of lactation activities,it is significantly higher in the late lactation period than in the lactation peak period.The relative protein at the level of mRNA should be significantly or extremely significantly lower than that of yak during lactation.4.At the protein level,the expression of LPL in lactation stage(peak stage,late stage)was significantly higher than that in quiescence stage and development stage(P < 0.01).The expression of CD36 was significantly higher than that of LPL(P < 0.01).The expression of FASN was the same as that of CD36.ACC ? increased significantly with the development of mammary gland(P.The expression of SCD1 in resting and developing stage was significantly lower than that in breast tissue in peak lactation and later stage.There are significant or extremely significant differences in the expression of SCD1 in the mammary gland of lactating dairy cows except that there is no difference between SCD1 and yak.The results show that the LPL,CD36,SCD1 genes have an increasing trend from the resting stage to the developmental stage to the lactation stage.The FASN gene has the highest expression during the resting period,then it will be in a relatively stable state,and the expression regularity of ACACA is not strong.In protein expression,LPL,CD36,FASN,ACC?,and SCD1 have an increasing trend from the resting period to the developmental period to the lactation peak period,indicating that these enzymes play an important role in the synthesis of milk fat.Among fatty acid sources,the ability of the mammary gland to synthesize itself plays a more important role.The difference in the breast tissue of lactating cows also mainly comes from the de novo synthesis.On the other hand,the difference in FASN expression in the catheter system between yak and dairy cows may also be the reason for the high milk fat rate of yak.