A TI{T-STEP.TagRFP-T} cassette has been knocked in to the endogenous Csas locus, resulting in Csas tagged at the C-terminal end with TagRFP-T. The tag sequence is preceeded by the linker sequence "AYALMKEYYVILSSS", where AYA is derived from the cloning procedure, LMKEYYVILSS is the translated RSRT recombinase target site and S is derived from the cloning procedure. The tag can be converted to EGFP in a tissue-specific manner (generating the Csas^KI-GFP allele) by using RSR recombinase to excise the RSRT cassette that includes the TagRFP-T tag.