Figure 1.

The ventricular-subventricular zone (V-SVZ) niche contains ependymal cells (gray) that contact the lateral ventricle and cerebrospinal fluid (CSF). Neural stem cells (NSCs; blue) have an apical contact with the CSF and a basal contact with the vasculature (red). In the human, astrocytic processes (blue) lie beneath the ependyma. Neurons (green) from the brain parenchyma innervate the niche. Surveying or resting microglia (brown) surveil the niche microenvironment and can become activated in the presence of tumor cells. Three proposed roles of the niche in malignant brain tumors are depicted. Left panel: Neural stem cells may acquire mutations that lead to cancer (purple). Middle panel: Neural stem cells can home toward tumors and eliminate tumor cells. Right panel: Tumor cells can migrate toward the V-SVZ and take up residence in the niche. A subset of factors demonstrated to be involved in these regions and discussed in the text (Direction from the Top: CSF Factors in Normal and Malignant Biology, Local Associations: Cellular Constituents of the Niche, Basal Foundations: Vascular Contact, The Niche as a Refuge) are listed on the right. BDNF, brain-derived neurotrophic factor; FGF, fibroblast growth factor; IGF2, insulin-like growth factor 2; NLGN-3, neuroligin-3; PEDF, pigment epithelium-derived factor; PIGF-2, placental growth factor 2; SDF-1, stromal-derived factor 1; VEGF, vascular endothelial growth factor.