Exon junction array detection of the 4.1R exon 16 splicing switch. Probe sets in the exon 16 region that exhibit significant changes in relative expression between day 7 and day 14 were mapped to the human genome using the UCSC BLAT alignment tool. (Bottom) The exon structure of the 2 mRNA isoforms expressed from the 4.1R gene; arrow represents alternative exon 16. (Top) Probe sets interrogating the exon 16 inclusion event were up-regulated at day 14, whereas a reciprocal decrease in expression of the exons 13 to 17 skipping event was observed. RT-PCR validation of this splicing switch is shown in Figure 1. Alternative exons 14 and 15 are not expressed in these cultures.