Gene transfer into bovine cells and embryos using replication‐defective retroviral vectors encapsidated with xenotropic murine leukemia virus envelopes

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Abstract
The amphotropic murine leukemia virus (MLV) env gene has been the most commonly used among the three kinds of MLV in retroviral vector systems due to its wide host range. On bovine target cells, however, we demonstrated that retroviral vectors packaged with xenotropic MLV envelope proteins were more than 500‐fold more infectious compared to the same vectors packaged with amphotropic MLV envelope proteins. This result indicates that the xenotropic MLV env gene is potentially more useful than the amphotropic MLV env in experiments designed to transfer genes to cells derived from non‐murine species. In a test of internal promoter activity in a retroviral vector, herpes simplex virus type 1 thymidine kinase (TK), simian virus 40 (SV40), human histone H4 and rat β‐actin promoters worked well in bovine cells. Finally, by co‐culture of bovine blastocysts and xenotropic MLV‐based virus‐producing cells, we infected the embryos with viruses encapsidated with xenotropic MLV envelope proteins. Infection of the embryo was confirmed by detection of the embryonic cells expressing E. coli β‐galactosidase gene under the rat β‐actin promoter which was transferred by retrovirus‐mediated infection.