Hif1a exon I.1 and exon I.2-containing mRNA isoforms are detectable in most mouse tissues. RT-PCR analysis of total RNA isolated from the indicated mouse tissue. PCR was performed using forward primers unique to either exon I.1 or exon I.2 and a common reverse primer specific for exon III. Single PCR products were indicative for the exon I.1 (371 bp) or the exon I.2 (472 bp) mRNA isoform. Representative results of two to five independent experiments are shown. Note that the exon I.1 mRNA isoform could not be detected in liver.