CMV-driven expression of green fluorescent protein (GFP) in male germ cells of transgenic mice and its effect on fertility

To determine if the expression of green fluorescent protein (GFP) during sp ermatogenesis can compromise the fertility of transgenic animals, we have p roduced mouse transgenic lines expressing GFP in the testis under the contr ol of the potent immediate early promoter and enhancer region of the human cytomegalovirus (CMV). GFP expression was detected in the germ cells with n o apparent effect on the fertility of any of the five transgenic lines stud ied. We demonstrate that the CMV promoter is transcriptionally active in th e testes of mice aged 7 days. However, protein could be visually detected o nly after day 10. GFP was not found either in mature spermatozoa or in Sert oli cells, but it was evident in round spermatids from seminiferous tubules and in cytoplasmic drops of spermatozoa from the epididymis. We also detec ted GFP in spermatogonia expressing c-kit, which indicates that GFP express ion driven by the CMV promoter takes place during the proliferative phase o f spermatogenesis. The expression of GFP during spermatogenesis did not aff ect the fertility of transgenic mice.