Abstract: In order to eliminate the potential biosafety risk of marker genes in transgenic animals by nuclear transfer,the Cre/Loxp system was used to delete the marker genes of the transgenic goat mammary epithelial cells（GMECs）with human lactoferrin（hLF）,so as to explore the effect of marker gene deletion on the mammary gland specific expression of functional genes. First,the transgenic hLF goat mammary epithelial cells were revived and purified. Then,the purified PBS185 plasmid was electrotransfected into mammary epithelial cells. After 10-14 d culture,the monoclonal cells were selected by self-made mouth-controlled transfer needle and trypsinase digested cells. Finally,whether or not the deletion of the marker gene was detected by PCR,prolactin nduced expression and the expression level of functional protein hLF was detected by ELISA and Western Blot. The results showed that a total of 65 monoclonal mammary epithelial cells were obtained after electrotransfection,and 18 of the cells in fine condition were detected by PCR. Among them,3 cell lines were deleted marker gene,and the deletion efficiency was 16.7%（3/18）. Moreover,the expression level of marker gene-deleted cell lines increased about 8 times （2.85 g·L^-1/0.35 g·L^-1）,the size of protein band was consistent with the target protein（80 kD）. The above results prove that the Cre/Loxp system can effectively delete the marker gene in GMECs genome and the expression level of cell lines significantly increase. Moreover,a system for the deletion of the marker gene in transgenic GMECs is successfully established,which also lays a foundation for the further expanding the production of transgenic goats without the marker gene.

Key words: marker gene, Cre/Loxp, hLF, mammary epithelial cells, induction