TEK and myeloproliferative neoplasm: To study the effects of the JAK2V617F-bearing vascular niche on MPN disease development in vivo, we crossed mice that bear a Cre-inducible human JAK2V617F gene (FF1) (12) with Tie2-Cre mice (33) to express JAK2V617F specifically in all hematopoietic cells and ECs (Tie2FF1).