UBE2I and neoplasm: Finally, we show that SUMOylation plays a role in cell proliferation and cycle in NSCs, leading to higher growth rates and self-renewal in vitro. The consequences of these effects were negligible in vivo, as we found that the fraction of proliferating cells was similar between mice grafted with Ubc9 NSCs and WT NSCs, with no evidence of mass formation/neoplasia in either group.