AQP4 and central nervous system cancer: Of these, AQP4 has previously been shown to be differentially expressed in quiescent astrocytes (Yoneda et al, 2001); HOPX is a marker of quiescent radial glial neural progenitors (Berg et al, 2019); NDRG2 is up‐regulated in G0/G1 arrested glioma cells (Li et al, 2012, 2); S100B is a chemoattractant for tumor‐associated macrophages (Wang et al, 2013); and TTYH1 is required to maintain NSC stemness via its role in activating the Notch signaling pathway (Kim et al, 2018, 1).