Enhancers that direct gene expression to central nervous system vascular endothelial cells

CNS vascular endothelial cells (ECs) exhibit a distinctive gene expression program that isfoundational for the blood-brain barrier (BBB). Previous research identified candidate cisregulatoryelements (CREs) that were hypothesized to control this program. In the present work,transgenic mice and recombinant adeno-associated virus vectors (rAAVs) have been used tointerrogate these candidate CREs. These experiments show that an 850 bp genomic DNAsegment derived from an evolutionarily conserved region of brain EC-specific accessiblechromatin possesses enhancer activity that is specific for BBB+ CNS ECs. An rAAV screen of>8,000 genomic DNA segments derived from CNS EC-specific CRE candidates reveals severalhundred with enhancer activity. Transcription factors ERG and LEF1 are shown to occupy sitesin brain ECs that are highly enriched in candidate and experimentally validated CREs, lendingstrong support to a model in which canonical Wnt signaling activates the BBB program bystabilizing the LEF1 partner beta-catenin.