UNIFORM VASCULAR-ENDOTHELIAL-CELL-SPECIFIC GENE-EXPRESSION IN BOTH EMBRYONIC AND ADULT TRANSGENIC MICE

TIE2 is a vascular endothelial-specific receptor tyrosine kinase essen tial for the regulation of vascular network formation and remodeling. Previously, we have shown that the 1.2-kb 5' flanking region of the TI E2 promoter is capable of directing beta-galactosidase reporter gene e xpression specifically into a subset of endothelial cells (ECs) of tra nsgenic mouse embryos, However, transgene activity: was restricted to early embryonic stages and not detectable rn adult mice, Herein we des cribe the identification and characterization of an autonomous endothe lial-specific enhancer in the first intron of the mouse TIE2 gene, Fur thermore, combination of the TIE2 promoter with an intron fragment con taining this enhancer allows it to target reporter gene expression spe cifically and uniformly to virtually all vascular ECs throughout Embry ogenesis and adulthood, To our knowledge, this is the first time that an in, vivo expression system has been assembled by which heterologous genes can be targeted exclusively to the ECs of the entire vasculatur e. This should he a valuable tool to address the function of genes dur ing physiological and pathological processes of vascular ECs in vivo. Furthermore, we were able to identify a short region critical for enha ncer function in vivo that contains putative binding sites for Ets-lik e transcription factors, This should, therefore, allow us to determine the molecular mechanisms underlying the vascular-EC-specific expressi on of the TIE2 gene.