Harnessing of the nucleosome-remodeling-deacetylase complex controls lymphocyte development and prevents leukemogenesis.

Cell fate depends on the interplay between chromatin regulators and transcription factors. Here we show that activity of the Mi-2ß nucleosome-remodeling and histone-deacetylase (NuRD) complex was controlled by the Ikaros family of lymphoid lineage-determining proteins. Ikaros, an integral component of the NuRD complex in lymphocytes, tethered this complex to active genes encoding molecules involved in lymphoid differentiation. Loss of Ikaros DNA-binding activity caused a local increase in chromatin remodeling and histone deacetylation and suppression of lymphoid cell-specific gene expression. Without Ikaros, the NuRD complex also redistributed to transcriptionally poised genes that were not targets of Ikaros (encoding molecules involved in proliferation and metabolism), which induced their reactivation. Thus, release of NuRD from Ikaros regulation blocks lymphocyte maturation and mediates progression to a leukemic state by engaging functionally opposing epigenetic and genetic networks.

Alternative promoter usage at the Notch1 locus supports ligand-independent signaling in T cell development and leukemogenesis.

Loss of the transcription factor Ikaros is correlated with Notch receptor activation in T cell acute lymphoblastic leukemia (T-ALL). However, the mechanism remains unknown. We identified promoters in Notch1 that drove the expression of Notch1 proteins in the absence of a ligand. Ikaros bound to both canonical and alternative Notch1 promoters and its loss increased permissive chromatin, facilitating recruitment of transcription regulators. At early stages of leukemogenesis, increased basal expression from the canonical and 5'-alternative promoters initiated a feedback loop, augmenting Notch1 signaling. Ikaros also repressed intragenic promoters for ligand-independent Notch1 proteins that are cryptic in wild-type cells, poised in preleukemic cells, and active in leukemic cells. Only ligand-independent Notch1 isoforms were required for Ikaros-mediated leukemogenesis. Notch1 alternative-promoter usage was observed during T cell development and T-ALL progression. Thus, a network of epigenetic and transcriptional regulators controls conventional and unconventional Notch signaling during normal development and leukemogenesis.

Spatial organization of the flow of genetic information in bacteria.

Eukaryotic cells spatially organize mRNA processes such as translation and mRNA decay. Much less is clear in bacterial cells where the spatial distribution of mature mRNA remains ambiguous. Using a sensitive method based on quantitative fluorescence in situ hybridization, we show here that in Caulobacter crescentus and Escherichia coli, chromosomally expressed mRNAs largely display limited dispersion from their site of transcription during their lifetime. We estimate apparent diffusion coefficients at least two orders of magnitude lower than expected for freely diffusing mRNA, and provide evidence in C. crescentus that this mRNA localization restricts ribosomal mobility. Furthermore, C. crescentus RNase E appears associated with the DNA independently of its mRNA substrates. Collectively, our findings show that bacteria can spatially organize translation and, potentially, mRNA decay by using the chromosome layout as a template. This chromosome-centric organization has important implications for cellular physiology and for our understanding of gene expression in bacteria.

Transcriptional regulation of the Ikzf1 locus.

Ikaros is a critical regulator of lymphocyte development and homeostasis; thus, understanding its transcriptional regulation is important from both developmental and clinical perspectives. Using a mouse transgenic reporter approach, we functionally characterized a network of highly conserved cis-acting elements at the Ikzf1 locus. We attribute B-cell and myeloid but not T-cell specificity to the main Ikzf1 promoter. Although this promoter was unable to counter local chromatin silencing effects, each of the 6 highly conserved Ikzf1 intronic enhancers alleviated silencing. Working together, the Ikzf1 enhancers provided locus control region activity, allowing reporter expression in a position and copy-independent manner. Only 1 of the Ikzf1 enhancers was responsible for the progressive upregulation of Ikaros expression from hematopoietic stem cells to lymphoid-primed multipotent progenitors to T-cell precursors, which are stages of differentiation dependent on Ikaros for normal outcome. Thus, Ikzf1 is regulated by both epigenetic and transcriptional factors that target its enhancers in both redundant and specific fashions to provide an expression profile supportive of normal lymphoid lineage progression and homeostasis. Mutations in the Ikzf1 regulatory elements and their interacting factors are likely to have adverse effects on lymphopoiesis and contribute to leukemogenesis.

Better tests, better care: improved diagnostics for infectious diseases.

In this IDSA policy paper, we review the current diagnostic landscape, including unmet needs and emerging technologies, and assess the challenges to the development and clinical integration of improved tests. To fulfill the promise of emerging diagnostics, IDSA presents recommendations that address a host of identified barriers. Achieving these goals will require the engagement and coordination of a number of stakeholders, including Congress, funding and regulatory bodies, public health agencies, the diagnostics industry, healthcare systems, professional societies, and individual clinicians.