Creation of low-copy integrated transgenic lines in Caenorhabditis elegans

In Caenorhabditis elegans, transgenic lines are typically created by inject ing DNA into the hermaphrodite germline to form multicopy extrachromosomal DNA arrays. This technique is a reliable means of expressing transgenes in C. elegans, but its use has limitations. Because extrachromosomal arrays ar e semistable, only a fraction of the animals in a transgenic extrachromosom al array line are transformed. In addition, because extrachromosomal arrays can contain hundreds of copies of the transforming DNA, transgenes may be overexpressed, misexpressed, or silenced. We have developed an alternative method for C. elegans transformation, using microparticle bombardment, that produces single- and low-copy chromosomal insertions. Using this method, w e find that it is possible to create integrated transgenic lines that repro ducibly express GFP reporter constructs without the variations in expressio n level and pattern frequently exhibited by extrachromosomal array lines. I n addition, we find that low-copy integrated lines can also be used to expr ess transgenes in the C. elegans germline, where conventional extrachromoso mal arrays typically fail to express due to germline silencing.