Comparison of the Expression Levels of EGFP Gene Driven by CMV Promoter in Different Tissues of the Transgenic Pigs (Sus scrofa) and Mice (Mus musculus)
Abstract：The CMV promoter is often used as a transcriptional regulatory sequence in eukaryotic expression vectors, and considered as a universal element capable of transcriptional activity in a wide rang of cells in vitro. However, reports documenting the transcriptional activity of this control element in different tissues of transgenic animals are relatively less. In this study, we produced the CMV-EGFP integrated transgenic pigs (Sus scrofa) through somatic cell nuclear transfer technique and CMV-EGFP integrated transgenic mice (Mus musculus) through pronuclear microinjection. Transgenic positive animals were identified through PCR screen. Then the expression level of reporter gene EGFP was investigated in liver, heart and muscle of the transgenic pigs through qPCR assay. The results showed that EGFP is most abundant in heart, and modest in muscle, and relatively less abundant in liver. We further examined the expression pattern of EGFP in a variety of tissues in both transgenic pigs and mice through detecting the fluorescence signal from cryosections. The results showed that the CMV promoter can drive EGFP expression in all the examined tissues of transgenic pigs and mice, but on closer inspection, we found that the fluorescence intensity of EGFP was obviously different in different tissues, where the signal was most strong in lung, small intestine and pancreas, modest in muscle and heart, and weak in spleen, kidney and liver of transgenic pigs. Similarly, expression level of EGFP was highest in lung, modest in brain, liver and muscle, and lower in spleen and kidney of transgenic mice. These experiment results suggested that the CMV promoter could drive the expression of EGFP in a wide range of tissues, however, its activity varies notably across different tissue, where it is most active in lung, modest active in muscle, and less active in kidney and spleen in both the transgenic pigs and transgenic mice. This study indicates that the abundance of transcription factors capable of activating the CMV promoter varies significantly in different tissues of animals. Therefore, whether to use the CMV promoter for establishing a transgenic animal model, should be base on the targeted expression site of the extragenous gene in the animal.
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