Gene transfer in bovine blastocysts using replication‐defective retroviral vectors packaged with gibbon ape leukemia virus envelopes

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Abstract
With this work we demonstrate that murine leukemia virus (MLV)‐based replication‐defective retroviral vectors encapsidated with Gibbon ape leukemia virus (GaLV) envelopes are significantly more infectious to bovine embryonic trachea (EBTr) cells than vectors encapsidated with murine xenotropic envelope proteins. In a test of internal promoter activity in an MLV retroviral vector, the rat β‐actin promoter was shown to be better than the herpes simplex virus type 1 thymidine kinase (TK) and human cytomegalovirus (CMV) immediate early promoters for the expression of an E. coli β‐galactosidase marker gene in bovine target cells. By co‐culture of bovine blastocysts and virus‐producing cells, or by culture of embryos in the medium harvested from virus‐producing cells, we transferred the E. coli β‐galactosidase gene into trophoblasts and also into inner cell mass (ICM) cells of a bovine embryo through the infection of the MLV‐based replication‐defective retroviruses encapsidated with GaLV envelope proteins. The infection was confirmed by the expression of the E. coli β‐galactosidase gene under a β‐actin internal promoter. In addition, co‐culture of ICM cells with virus‐producing cells resulted in differentiation of ICM cells into embryoid bodies expressing the marker genes.