Murine embryo development following cytoplasmic injection of linear and condensed DNA

In 1985 Brinster et al. [1] observed that linearized DNA injected in the cytoplasm of mouse zygotes underwent spontaneous supercoiling within 24 h. This finding suggests that DNA prefers and functions best in tertiary structure. In an effort to improve the efficiency of transgenesis by cytoplasmic injection, DNA was condensed with MgCl2 to form a three dimensional rod-shaped DNA prior to injection in pronuclear stage murine zygotes. The DNA used was enhanced green fluorescent protein on a cytomegalovirus promoter (CMV-EGFP) and served as a marker for gene integration and protein expression in culture conditions. The condensed CMV-EGFP construct was injected in the cytoplasm at 3 concentrations (100, n = 816; 425, n = 464; and 625 μg/ml, n = 708). For comparison linear CMV-EGFP construct was injected into the pronucleus (5 μg/ml, n = 196) and into the cytoplasm (625 μg/ml, n = 628). In all treatment groups the control and buffer injected embryos developed similarly. Among DNA treatment groups, the highest development of fluorescing embryos was observed in zygotes injected in the cytoplasm with linear CMV-EGFP (625 μg/ml); however, zygotes injected in the cytoplasm with condensed CMV-EGFP (625 μg/ml) had the highest percentage (44%) of fluorescing embryos, the highest percentage (16.7%) of fluorescing morula and blastocysts, and the lowest percentage of fluorescence mosaicism at every stage of embryo development after 4 d in culture; thereby making it the best method for generating transgenic animals.