APELA and neoplasm: Since APELA [10] and the Apelin receptor [13] have been shown to play important roles in vascular development and stem cell proliferation, we examined whether APELA and APLNR were expressed in a stem cell niche in GBM patient tumor tissue by testing both RNA in situ hybridization (ISH) and immunohistochemistry (IHC), and found that APELA/APLNR-expressing cells were localized in a putative stem cell niche.