PYCR1 and central nervous system cancer: In light of our previous data suggesting that PYCR1 was the major determinant of IDH1R132H-driven increased proline synthesis from glutamine in glioma (Hollinshead et al., 2018), we also assessed glutamine-derived proline and noted that knockdown of PYCR1 but not PYCR2 led to a decrease in the proportion of proline derived from glutamine in both normoxia and hypoxia (Figure 1G).