Efficient gene transfer by hybrid retroviral vectors to murine spermatogenic cells

Using murine spermatogenic cell lines GC-1 spg and GC-2 spd(ts) as target cells, an attempt was made to design a retroviral vector that would transduce genes efficiently. Promoter activities of various retroviral long terminal repeats (LTRs) were examined by using chloramphenicol acetyltransferase (CAT) as a reporter. The U3 region of spleen focus-forming virus (SFFVp) showed higher enhancer activity than that of Moloney murine leukemia virus (Mo-MuLV) in both cell lines. The U3 region of myeloproliferative sarcoma virus (MPSV) showed higher activity only in GC-1 spg cells. Expression was suppressed by the repressor element of the primer-binding site (PBS) of the Moloney-related virus. The efficiency of transduction of the multidrug-resistance gene (mdr-1) by an Mo-MuLV-based vector was compared with hybrid vectors consisting of the murine embryonic stem cell virus (MESV) PBS and the LTR of either SFFVp or MPSV. Rhodamine efflux assays and colchicine-resistant colony-forming assays demonstrated higher gene expression by the hybrid vectors. Amphotropic and ecotropic receptors were found to be expressed and functional in both cell lines. Thus, these hybrid vectors represent a powerful tool by which to transfer genes into spermatogenic cells.