Transient expression of DNA after ballistic introduction into Drosophila embryos.

Current procedures for introduction of DNA into Drosophila embryos require the time-consuming microinjection of DNA solution into individual embryos (1, 2). A procedure has recently been used successfully in plants, yeast and cultured cells for the ballistic introduction of DNA via tungsten (W) particles (3-5) . Using a modification of this procedure for Drosophila embryos, we have obtained transient expression at high efficiency. The technique also has the potential to be useful for germ line transformation. All incubations and procedures were at room temperature. DNA [a total of 1 —20 /ig of a 1 /*g//d solution in embryo injection buffer (0.1 mM sodium phosphate pH 6.8, 5 mM KC1)] was precipitated onto washed W particles (1.2 /*m diameter, obtained from Biolistics, Inc.) in a total volume of 65 p\, according to the recommendations of the manufacturer. After the DNA precipitation step, 50 /tl of supernatant was removed (without centrifugation). The tube containing the remaining pellet and residual supernatant (12 -15 /tl) was vortexed just before applying 8 /tl of this sample to the macroprojectile. Embryos (approximately 10—20,000), collected for 1 hr from a cage of w" flies onto yeasted apple juice agar plates, were dechorionated for 3 min with 50% bleach and spread out on a circle of wet Whatman # 1 filter paper. The filter was then blotted on paper towels, transferred to a fresh apple juice agar plate (10x1.5 cm) and the embryos on the filter bombarded with the DNA-carrying W particles, using a Biolistics bioparticle delivery system (DuPont) (3).