We described the instructive function of endothelial Jagged1 in supporting self-renewal and the regenerative capacity of HSCs in the adult BM vascular niche [27], as well as its function in inducing aggressiveness and chemoresistance in lymphoma [13], breast cancer cells [18,19] and, more recently, in ovarian cancer [21]. The gene discussed is JAG1; the disease is breast carcinoma.