GENE-TRANSFER IN BOVINE BLASTOCYSTS USING REPLICATION-DEFECTIVE RETROVIRAL VECTORS PACKAGED WITH GIBBON APE LEUKEMIA-VIRUS ENVELOPES

With this work we demonstrate that murine leukemia virus (MLV)-based r eplication-defective retroviral vectors encapsidated with Gibbon ape l eukemia virus (GaLV) envelopes are significantly more infectious to bo vine embryonic trachea (EBTr) cells than vectors encapsidated with mur ine xenotropic envelope proteins. In a test of internal promoter activ ity in an MLV retroviral vector, the rat beta-actin promoter was shown to be better than the herpes simplex virus type 1 thymidine kinase (T K) and human cytomegalovirus (CMV) immediate early promoters for the e xpression of an E coli beta-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 beta-galactosidase gene into trophob lasts and also into inner cell mass (ICM) cells of a bovine embryo thr ough 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 beta-galactosidase gene under a beta- actin internal promoter. In addition, co-culture of ICM cells with vir us-producing cells resulted in differentiation of ICM cells into embry oid bodies expressing the marker genes.