Manipulating AV endothelial cell specification. When endothelial cells from a human umbilical vein (HUVEC) or artery (HUAEC) are freshly isolated (HUVEC-F, HUAEC-F), their gene expression profiles can be readily distinguished. Culture of the endothelial cells (HUVEC-C and HUAEC-C) erases the differential AV gene expression, partly due to loss of Notch activity. The arterial-specific gene profile can, however, be induced in HUVEC-C by combined overexpression of 8 transcription factors (TF) (Prdm16, MSX1, EMX2, NKX2-3, TOX2, Hey2, SOX17, and Aff3), which together are more effective than any one alone, including HEY2, a Notch effector (not shown).