Mice transgenic for a c-myc gene driven by the IgH enhancer (E mu-myc) were shown to almost invariably develop lymphomas, 90% succumbing in the first 5 mo of life. The tumors typically presented as rapidly progressive lymphadenopathy with thymic involvement and were highly malignant by transplantation assay. Morphologically, they were lymphoblastic lymphomas, usually accompanied by lymphoid leukemia and granulocytosis, and were distinct from the tumors that arose much later in 37% of nontransgenic mice of the same (C57BL/6 x SJL)F2 genetic background. Cell-surface markers on 31 E mu-myc tumors identified 52% as pre-B lymphomas, 29% as mixed pre-B and B lymphomas, and 19% as B lymphomas. The tumors appeared to arise at random from a population of pre-B cells expanded by constitutive expression of the myc transgene. A majority of the animals initiated malignancy at the rate of 17% per week. The rate at which the cycling, benign pre-B cells spontaneously convert to malignancy was estimated to about 10(-10) per cell per generation. A transient leukocytosis identified in young E mu-myc mice was developed into a rapid assay for inheritance of the transgene.

Bcl2 family proteins control mitochondrial apoptosis and its members exert critical cell type and differentiation stage-specific functions, acting as barriers against autoimmunity or transformation. Anti-apoptotic Bcl2a1/Bfl1/A1 is frequently deregulated in different types of blood cancers in humans but its physiological role is poorly understood as quadruplication of the Bcl2a1 gene locus in mice hampers conventional gene targeting strategies. Transgenic overexpression of A1, deletion of the A1-a paralogue or constitutive knockdown in the hematopoietic compartment of mice by RNAi suggested rate-limiting roles in lymphocyte development, granulopoiesis and mast cell activation. Here we report on the consequences of conditional knockdown of A1 protein expression using a reverse transactivator (rtTA)-driven approach that highlights a critical role for this Bcl2 family member in the maintenance of mature B-cell homeostasis. Furthermore, we define the A1/Bim (Bcl-2 interacting mediator of cell death) axis as a target of key kinases mediating B-cell receptor (BCR)-dependent survival signals, such as, spleen tyrosine kinase (Syk) and Brutons tyrosine kinase (Btk). As such, A1 represents a putative target for the treatment of B-cell-related pathologies depending on hyperactivation of BCR-emanating survival signals and loss of A1 expression accounts, in part, for the pro-apoptotic effects of Syk- or Btk inhibitors that rely on the 'BH3-only' protein Bim for cell killing.

Drug discovery is a key part of malaria control and eradication strategies, and could benefit from sensitive and affordable assays to quantify parasite growth and to help identify the targets of potential anti-malarial compounds. Bioluminescence, achieved through expression of exogenous luciferases, is a powerful tool that has been applied in studies of several aspects of parasite biology and high throughput growth assays. We have expressed the new reporter NanoLuc (Nluc) luciferase in Plasmodium falciparum and showed it is at least 100 times brighter than the commonly used firefly luciferase. Nluc brightness was explored as a means to achieve a growth assay with higher sensitivity and lower cost. In addition we attempted to develop other screening assays that may help interrogate libraries of inhibitory compounds for their mechanism of action. To this end parasites were engineered to express Nluc in the cytoplasm, the parasitophorous vacuole that surrounds the intraerythrocytic parasite or exported to the red blood cell cytosol. As proof-of-concept, these parasites were used to develop functional screening assays for quantifying the effects of Brefeldin A, an inhibitor of protein secretion, and Furosemide, an inhibitor of new permeation pathways used by parasites to acquire plasma nutrients.

Platelets are anuclear cells that are essential for blood clotting. They are produced by large polyploid precursor cells called megakaryocytes. Previous genome-wide association studies in nearly 70,000 individuals indicated that single nucleotide variants (SNVs) in the gene encoding the actin cytoskeletal regulator tropomyosin 4 (TPM4) exert an effect on the count and volume of platelets. Platelet number and volume are independent risk factors for heart attack and stroke. Here, we have identified 2 unrelated families in the BRIDGE Bleeding and Platelet Disorders (BPD) collection who carry a TPM4 variant that causes truncation of the TPM4 protein and segregates with macrothrombocytopenia, a disorder characterized by low platelet count. N-Ethyl-N-nitrosourea-induced (ENU-induced) missense mutations in Tpm4 or targeted inactivation of the Tpm4 locus led to gene dosage-dependent macrothrombocytopenia in mice. All other blood cell counts in Tpm4-deficient mice were normal. Insufficient TPM4 expression in human and mouse megakaryocytes resulted in a defect in the terminal stages of platelet production and had a mild effect on platelet function. Together, our findings demonstrate a nonredundant role for TPM4 in platelet biogenesis in humans and mice and reveal that truncating variants in TPM4 cause a previously undescribed dominant Mendelian platelet disorder.

Several novel therapeutics are poised to change the natural history of chronic lymphocytic leukaemia (CLL) and the increasing use of these therapies has highlighted limitations of traditional disease monitoring methods. Here we demonstrate that circulating tumour DNA (ctDNA) is readily detectable in patients with CLL. Importantly, ctDNA does not simply mirror the genomic information contained within circulating malignant lymphocytes but instead parallels changes across different disease compartments following treatment with novel therapies. Serial ctDNA analysis allows clonal dynamics to be monitored over time and identifies the emergence of genomic changes associated with Richter's syndrome (RS). In addition to conventional disease monitoring, ctDNA provides a unique opportunity for non-invasive serial analysis of CLL for molecular disease monitoring.

Expression of VH-coded mRNA molecules in T cells, antigen-specific T cell lines, or T cell hybridomas was not detected using four different VH DNA probes under conditions that permitted cross-hybridization between distantly related VH genes. In contrast, VH gene expression was readily detected in two B cell lymphomas and in splenic B cells. Less than one molecule per cell of RNA, exactly complementary to the DNA probes used, would have been detected in these T cell populations. The results thus seriously question the proposition that T cells use the B cell VH repertoire to code for antigen receptors.

It is well established that BAX and BAK play crucial, overlapping roles in the intrinsic pathway of apoptosis. Gene targeted mice lacking both BAX and BAK have previously been generated, but the majority of these animals died perinatally. BOK is a poorly studied relative of BAX and BAK that shares extensive amino acid sequence homology to both proteins, but its function remains largely unclear to date. To determine whether BOK plays an overlapping role with BAX and BAK, we utilized a hematopoietic reconstitution model where lethally irradiated wild type mice were transplanted with Bok(-/-)Bax(-/-)Bak(-/-) triple knockout (TKO) fetal liver cells, and compared alongside mice reconstituted with a Bax(-/-)Bak(-/-) double knockout (DKO) hematopoietic compartment. We report here that mice with a TKO and DKO hematopoietic system died at a similar rate and much earlier than control animals, mostly due to severe autoimmune pathology. Both TKO and DKO reconstituted mice also had altered frequencies of various leukocyte subsets in the thymus, bone marrow and spleen, displayed leukocyte infiltrates and autoimmune pathology in multiple tissues, as well as elevated levels of anti-nuclear autoantibodies. Interestingly, the additional deletion of BOK (on top of BAX and BAK loss) led to a further increase in peripheral blood lymphocytes, as well as enhanced lymphoid infiltration in some organs. These findings suggest that BOK may have some functions that are redundant with BAX and BAK in the hematopoietic system.

Autoimmunity, infectious diseases and cancer affect women and men differently. Because they tend to develop more vigorous adaptive immune responses than men, women are less susceptible to some infectious diseases but also at higher risk of autoimmunity. The regulation of immune responses by sex-dependent factors probably involves several non-redundant mechanisms. A privileged area of study, however, concerns the role of sex steroid hormones in the biology of innate immune cells, especially dendritic cells (DCs). In recent years, our understanding of the lineage origin of DC populations has expanded, and the lineage-committing transcription factors shaping peripheral DC subsets have been identified. Both progenitor cells and mature DC subsets express estrogen receptors (ERs), which are ligand-dependent transcription factors. This suggests that estrogens may contribute to the reported sex differences in immunity by regulating DC biology. Here, we review the recent literature and highlight evidence that estrogen-dependent activation of ERα regulates the development or the functional responses of particular DC subsets. The in vitro model of GM-CSF-induced DC differentiation shows that CD11c+ CD11bint Ly6cneg cells depend on ERα activation by estrogen for their development, and for the acquisition of competence to activate naive CD4+ T lymphocytes and mount a robust pro-inflammatory cytokine response to CD40 stimulation. In this model, estrogen signaling in conjunction with GM-CSF is necessary to promote early interferon regulatory factor (Irf)-4 expression in macrophage-DC progenitors and their subsequent differentiation into IRF-4hi CD11c+ CD11bint Ly6cneg cells, closely related to the cDC2 subset. The Flt3L-induced model of DC differentiation in turn shows that ERα signaling promotes the development of conventional DC (cDC) and plasmacytoid DC (pDC) with higher capability of pro-inflammatory cytokine production in response to TLR stimulation. Likewise, cell-intrinsic ER signaling positively regulates the TLR-driven production of type I interferons (IFNs) in mouse pDCs in vivo. This effect of estrogens likely contributes to the greater proficiency of women's pDCs than men's as regards the production of type I IFNs elicited by TLR7 ligands. In summary, evidence is emerging in support of the notion that estrogen signaling regulates important aspects of cDC and pDC development and/or effector functions, in both mice and humans.

The human pathogen Legionella pneumophila must evade host cell death signaling to enable replication in lung macrophages and to cause disease. After bacterial growth, however, L. pneumophila is thought to induce apoptosis during egress from macrophages. The bacterial effector protein, SidF, has been shown to control host cell survival and death by inhibiting pro-apoptotic BNIP3 and BCL-RAMBO signaling. Using live-cell imaging to follow the L. pneumophila-macrophage interaction, we now demonstrate that L. pneumophila evades host cell apoptosis independent of SidF. In the absence of SidF, L. pneumophila was able to replicate, cause loss of mitochondria membrane potential, kill macrophages, and establish infections in lungs of mice. Consistent with this, deletion of BNIP3 and BCL-RAMBO did not affect intracellular L. pneumophila replication, macrophage death rates, and in vivo bacterial virulence. Abrogating mitochondrial cell death by genetic deletion of the effectors of intrinsic apoptosis, BAX, and BAK, or the regulator of mitochondrial permeability transition pore formation, cyclophilin-D, did not affect bacterial growth or the initial killing of macrophages. Loss of BAX and BAK only marginally limited the ability of L. pneumophila to efficiently kill all macrophages over extended periods. L. pneumophila induced killing of macrophages was delayed in the absence of capsase-11 mediated pyroptosis. Together, our data demonstrate that L. pneumophila evades host cell death responses independently of SidF during replication and can induce pyroptosis to kill macrophages in a timely manner.

Remarkably little is known about how intracellular pathogens exit the host cell in order to infect new hosts. Pathogenic chlamydiae egress by first rupturing their replicative niche (the inclusion) before rapidly lysing the host cell. Here we apply a laser ablation strategy to specifically disrupt the chlamydial inclusion, thereby uncoupling inclusion rupture from the subsequent cell lysis and allowing us to dissect the molecular events involved in each step. Pharmacological inhibition of host cell calpains inhibits inclusion rupture, but not subsequent cell lysis. Further, we demonstrate that inclusion rupture triggers a rapid necrotic cell death pathway independent of BAK, BAX, RIP1 and caspases. Both processes work sequentially to efficiently liberate the pathogen from the host cytoplasm, promoting secondary infection. These results reconcile the pathogen's known capacity to promote host cell survival and induce cell death.

DNA-binding proteins are central regulators of chromosome organization; however, in genome-reduced bacteria their diversity is largely diminished. Whether the chromosomes of such bacteria adopt defined three-dimensional structures remains unexplored. Here we combine Hi-C and super-resolution microscopy to determine the structure of the Mycoplasma pneumoniae chromosome at a 10 kb resolution. We find a defined structure, with a global symmetry between two arms that connect opposite poles, one bearing the chromosomal Ori and the other the midpoint. Analysis of local structures at a 3 kb resolution indicates that the chromosome is organized into domains ranging from 15 to 33 kb. We provide evidence that genes within the same domain tend to be co-regulated, suggesting that chromosome organization influences transcriptional regulation, and that supercoiling regulates local organization. This study extends the current understanding of bacterial genome organization and demonstrates that a defined chromosomal structure is a universal feature of living systems.

The Eμ-Myc mouse is an extensively used model of MYC driven malignancy; however to date there has only been partial characterization of MYC co-operative mutations leading to spontaneous lymphomagenesis. Here we sequence spontaneously arising Eμ-Myc lymphomas to define transgene architecture, somatic mutations, and structural alterations. We identify frequent disruptive mutations in the PRC1-like component and BCL6-corepressor gene Bcor. Moreover, we find unexpected concomitant multigenic lesions involving Cdkn2a loss and other cancer genes including Nras, Kras and Bcor. These findings challenge the assumed two-hit model of Eμ-Myc lymphoma and demonstrate a functional in vivo role for Bcor in suppressing tumorigenesis.