CXCR4 and neoplasm: Since it is reported that the tumor tropism of NSCs is regulated by hypoxia-related signaling pathways [7], the mRNA expression alternation of hypoxia-related signal receptors, c-Met, CXCR4, c-Kit, and VEGFR2, in NSCs upon hypoxia treatment was measured by qPCR (Figure 2(a)).