The VEGF-A exon 8 splicing-sensitive fluorescent reporter mouse is a novel tool to assess the effects of splicing regulatory compounds <i>in vivo</i>

Vascular endothelial growth factor <i>(VEGF)-A</i> is differentially spliced to give two functionally different isoform families; pro-angiogenic, pro-permeability VEGF-A_xxx and anti-angiogenic, anti-permeability VEGF-A_xxxb. <i>VEGF-A</i> splicing is dysregulated in several pathologies, including cancer, diabetes, and peripheral arterial disease. The bichromatic VEGF-A splicing-sensitive fluorescent reporter harboured in a transgenic mouse is a novel approach to investigate the splicing patterns of <i>VEGF-A in vivo</i>. We generated a transgenic mouse harbouring a splicing-sensitive fluorescent reporter designed to mimic <i>VEGF-A</i> terminal exon splicing (VEGF8ab) by insertion into the <i>ROSA26</i> genomic locus. dsRED expression denotes proximal splice site selection (VEGF-A_xxx) and eGFP expression denotes distal splice site selection (VEGF-A_xxxb). We investigated the tissue-specific expression patterns in the eye, skeletal muscle, cardiac muscle, kidney, and pancreas, and determined whether the splicing pattern could be manipulated in the same manner as endogenous <i>VEGF-A</i> by treatment with the SRPK1 inhibitor SPHINX 31. We confirmed expression of both dsRED and eGFP in the eye, skeletal muscle, cardiac muscle, kidney, and pancreas, with the highest expression of both fluorescent proteins observed in the exocrine pancreas. The ratio of dsRED and eGFP matched that of endogenous VEGF-A_xxx and VEGF-A_xxxb. Treatment of the VEGF8ab mice with SPHINX 31 increased the mRNA and protein eGFP/dsRED ratio in the exocrine pancreas, mimicking endogenous <i>VEGF-A</i> splicing. The <i>VEGF-A</i> exon 8 splicing-sensitive fluorescent reporter mouse is a novel tool to assess splicing regulation in the individual cell-types and tissues, which provides a useful screening process for potentially therapeutic splicing regulatory compounds <i>in vivo</i>