Addition of reversine to dividing cells ejects Mad1 and the RZZ complex from unattached kinetochores and prevents resolution of incorrect chromosome–microtubule attachments (see also related papers by Hewitt et al. and Maciejowski et al. in this issue).

FoxP3 ؉ regulatory T cells (Tregs) protect against autoimmunity, type 1 diabetes (T1D) in particular, prompting the hypothesis that a deficiency in Tregs is a critical determinant of diabetes susceptibility in NOD mice. However, tests of this hypothesis have yielded contradictory results. We confirmed that NOD mice, compared with reference strains, do not have a primary deficit in Treg numbers in the lymphoid organs, whether in prediabetic mice of any age or in animals with recent-onset diabetes. NOD Tregs did show a defect in standard in vitro T cell suppression assays, particularly at low suppressor/effector ratios. Gene expression profiling revealed the vast majority of transcripts constituting the ''Treg signature'' to be normally distributed in NOD Tregs versus CD4 ؉ T conventional (Tconv) cells, although there were a few differences affecting one or the other population. According to results from criss-cross experiments, the functional inefficacy was not rooted in NOD Tregs, which suppressed as well as their C57BL/6 (B6) counterparts, but rather in NOD Tconv, which were less prone to suppression than were B6 Tconv cells. They also responded more effectively to anti-CD3/28 monoclonal antibody (mAb) stimulation in vitro or to a natural pancreatic antigen in vivo. This difference was independent of autoimmune inflammation, did not map to the idd3 region, and was not due to the overproduction of interleukin-21 in NOD mice. That the immune dysregulation in this T1D model is rooted in the ability of effector T cells to be regulated, rather than in Tregs themselves, has implications for proposed therapeutic interventions.conventional T cells ͉ regulatory T cells ͉ type 1 diabetes

Key Points• Human hematopoietic cells develop within human iPSCderived teratomas in immunodeficient mice.• Co-transplantation of OP9 stromal cells along with human iPSCs increases hematopoietic specification within teratomas.

Immature thymocytes expressing autoreactive T-cell receptors (TCR) can adopt differing cell fates: clonal deletion by apoptosis or deviation into alternative lineages such as FoxP3 + regulatory T cells (Treg). We revisited the role of the transcription factor Nr4a1 (Nur77), an immediate-early response gene induced by TCR engagement. Nr4a1KO mice show clear quantitative defects in antigen-induced clonal deletion. The impact of the Nr4a1 deletion is not enhanced by deletion of the proapoptotic factor Bim. In addition, Nr4a1 curtails initial differentiation into the Treg lineage in TCR transgenic mice and in nontransgenic mice. Transcriptional profiling of Nr4a1KO thymocytes under selection conditions reveals that Nr4a1 activates the transcription of several targets, consistent with these diverse actions: (i) Nr4a1 partakes in the induction of Bim after TCR triggering; (ii) perhaps paradoxically, Nr4a1 positively controls several transcripts of the Treg signature, in particular Ikzf2 and Tnfrsf9; (iii) consistent with its prosurvival and metabolic role in the liver, Nr4a1 is also required for the induction by TCR of a coordinated set of enzymes of the glycolytic and Krebs cycle pathways, which we propose may antagonize Treg selection as does activation of mTOR/Akt. Thus, Nr4a1 appears to act as a balancing molecule in fate determination at a critical juncture of T-cell differentiation.glycolysis | immune tolerance | thymus | nuclear receptor A hallmark of the adaptive immune system is its ability to respond to the infinite repertoire of potential pathogens to which it might someday be exposed, but the undirected process of antigen receptor rearrangement in thymocytes generates receptors that are reactive to self and hence are potentially dangerous. Fledgling T cells carrying a nascent T-cell receptor (TCR) must undergo a rigorous process of negative selection, during which cells expressing a self-reactive TCR are eliminated by induced apoptosis or deviated to alternative differentiation pathways in which self-reactivity is defused [NKT, CD8αα, or FoxP3 + Triggering of mitochondrial apoptosis by signaling cascades downstream from the TCR is clearly established. Bim and Bax/ Bak, proapoptotic members of the mitochondrial apoptosis pathway, are essential for efficient negative selection (2, 3), but this may not be the sole mechanism. Early experiments involving blockade of RNA or protein synthesis suggested that negative selection is both transcription and translation dependent (4). Indeed, the transcription factor Nr4a1 has been implicated in negative selection (5, 6). An orphan member of the nuclear receptor superfamily and the Nr4a1/Nr4a2/Nr4a3 subfamily, Nr4a1 is a transcriptional activator, but can also promote mitochondrial apoptosis. In both tumor cell lines and thymocytes undergoing negative selection, Nr4a1 undergoes phosphorylation-dependent export from the nucleus to the mitochondria, where it conformationally alters Bcl-2 to promote apoptosis (7-10). Nr4a1 is associated with apoptosis in a number of phys...