A 264bp portion of scro exon 2 has been deleted (the deletion is just downstream of the start codon in this exon), and replaced with a sequence cassette that contains the EGFP coding sequence and a Equa\eqFP578TagRFP.3xP3 marker. This results in EGFP being expressed under the control of the regulatory sequences of the scro RA, RB and RC transcript isoforms, while expression of the native scro RA, RB and RC transcripts is disrupted due to the presence of an SV40 transcription termination signal downstream of the EGFP coding sequence. (Expression of the scro RF isoform is not affected by the insertion).