Schematic for the Production of a Modified BAC for the Targeted Expression of an XFP or an XFP-Based Reporter in Mice

<div><p>(A) A library of suitable BAC clones is scanned using bioinformatics and an appropriate clone, encoding a suitable cell-type-specific transcriptional unit with ample flanking regions, is selected. Note that only a few of the many possible enhancer and silencer regions are drawn. An exon that lies downstream of the ATC start sequence is selected to be replaced by the XFP/reporter sequence by homologous recombination (exon 2 in this example), and a shuttle vector that codes for the label together with flanking regions around the exon (“a” and “b”) is constructed. The enzyme RecA is used to interchange the sequence for the exon and the label to form a modified BAC clone that codes for the label. The modified clone is injected into a mouse oocyte, where the dominant incorporation into the host DNA occurs through nonhomologous recombination.</p> <p>(B) Many factors influence the phenotype of a given transgenic mouse, and thus the same clone may result in a number of lines with slightly different properties. The insert shows the XFP expression pattern for a line based on a BAC clone that contains the transcriptional unit of a glycine transporter.</p> <p>(Image: Jean-Marc Fritschy and Hanns-Ulrich Zeilhofer)</p>