Caenorhabditis elegans reporter fusion genes generated by seamless modification of large genomic DNA clones

By determining spatial-temporal expression pat- terns, reporter constructs provide significant insights into gene function. Although additionally providing information on subcellular distribution, translational reporters, where the reporter is fused to the gene coding sequence, are used less fre- quently than simpler constructs containing only putative promoter sequences. Because these latter constructs may not contain all necessary regulatory elements, resulting expression patterns must be interpreted cautiously. To ensure inclusion of all such elements and provide details of subcellular localization, construction of translational reporters would, preferably, utilize genomic clones, containing the complete locus plus flanking regions and permit seamless insertion of the reporter anywhere within the gene. We have developed such a method based upon l Red-mediated recombineering coupled to a robust two-step counter-selection protocol. We have inserted either gfp or cfp precisely at the C-termini of three Caenorhabditis elegans target genes, each located within different fosmid clones, and examined previously with conventional reporter approaches. Resulting transgenic lines revealed reporter expression consistent with previously pub- lished data for the tagged genes and also provided additional information including subcellular distri- butions. This simple and straightforward method generates reporters highly likely to recapitulate endogenous gene expression and thus represents an important addition to the functional genomics toolbox.