An 'isoTarget knockout' (iso-KO) cassette has been inserted into the endogenous Rdl locus, in the exon specific to the RG isoform (in a predicted surface-exposed loop). The iso-KO cassette consists of 1. an RSRT stop cassette containing multiple termination codons to ensure disruption of translation and 2. a Tag:V5 epitope. In the absence of RSR recombinase, this results in specific reduction in expression of the Rdl RG isoform.