Enhanced expression of VEGF-A in β cells increases endothelial cell number but impairs islet morphogenesis and β cell proliferation

► Islet cell and endothelial cell interactions are critical for islet development. ► VEGF-A from developing endocrine cells is critical for islet vascularization. ► Increased VEGF-A increases endothelial cells, but reduces β cell mass. ► Increased VEGF-A impairs β cell proliferation and migration and islet formation. ► Angiopoietin-Tie2 signaling does not have a crucial role in islet vascularization.