VEGR1 agonists PIGF-2 and VEGF-A stimulate VEGR1 on megakaryocytes (Mks) leading to CXCR4 upregulation and endomitosis. CXCR4-dependent migration of Mks results in localization of mature Mks to the vascular niche and platelet release into bone marrow sinusoids. PIGF indicates placental growth factor.