Differential requirement for nucleostemin in embryonic stem cell and neural stem cell viability.

Stem cells have the remarkable ability to self-renew and to generate multiple cell types. Nucleostemin is one of proteins that are enriched in many types of stem cells. Targeted deletion of nucleostemin in the mouse results in developmental arrest at the implantation stage, indicating that nucleostemin is crucial for early embryogenesis. However, the molecular basis of nucleostemin function in early mouse embryos remains largely unknown, and the role of nucleostemin in tissue stem cells has not been examined by gene targeting analyses due to the early embryonic lethality of nucleostemin null animals. To address these questions, we generated inducible nucleostemin null embryonic stem (ES) cells in which both alleles of nucleostemin are disrupted, but nucleostemin cDNA under the control of a tetracycline-responsive transcriptional activator is introduced into the Rosa26 locus. We show that loss of nucleostemin results in reduced cell proliferation and increased apoptosis in both ES cells and ES cell-derived neural stem/progenitor cells. The reduction in cell viability is much more profound in ES cells than in neural stem/progenitor cells, an effect that is mediated at least in part by increased induction and accumulation of p53 and/or activated caspase-3 in ES cells than in neural stem/progenitor cells.