Studies On The Effects Of Micronutrient Zinc (Zn) On β-Casein Synthesis And Secretion In Mammary Epithelial Cells Of Dairy Goats

The effects on proliferation of mammary epithelial cells, expression of IGF-Ⅰand IGF-Ⅰreceptor gene,IGF-Ⅰandβ-casein secretion by mammary epithelial cells cultured in medium R1640 containing different levels of ZnSO4 were studied in this thesis, which implements for manipulation ofβ-casein synthesis and secretion. Results were showed as follows:(1)β-casein synthesis was increased with the level of ZnSO4 increased in range 20-40μmol/L.Meantime the cell number was also increased. This result indicated that zinc regulatedβ-casein synthesis and secretion by increasing epithelial cell number.(2)IGF-Ⅰsecretion was increased with the level of ZnSO4 increased in range 10-40μmol/L.It showed that IGF-Ⅰsecretion was regulated by zinc. So nutritional status can direct effect IGF-Ⅰsynthesis and secretion.(3)With the level of ZnSO4 increased,either secration ofβ-casein and IGF-Ⅰor expression of IGF-Ⅰand IGF-Ⅰreceptor gene was increased,and they had significant correlation.The results suggested that there was a interaction on regulatingβ-casein synthesis and secretion between zinc and IGF-Ⅰ.(4)IGF-Ⅰcan stimulated Stat5 DNA binding activity.In conclusion,zinc can regulatedβ-casein synthesis and secretion by the way as follows:At first,zinc supported proliferation of mammary epithelial cells .With increasing cell number and expressin of IGF-Ⅰgene,IGF-Ⅰsecretion was increased. When IGF-Ⅰmolecule became attached to a receptor protein on the outside of the cell,phosphate (P) was made available to an enzyme inside the cell,which transfers the P to a Stat5 molecule. The activated Stat5 molecule attached to a part of the gene that holded the promoter region of genes which contain the DNA'recipe'forβ-casein. In response to Stat5 binding,the DNA produced a copy of its recipe in the form of messenger RNA which,in turn,was used as a template for the synthesis of casein which was secreted with other milk components into the alveoli of the mammary gland.