Induction of telomerase activity during development of human mast cells from peripheral blood CD34+ cells: comparisons with tumor mast-cell lines

To further characterize the development of mast cells from human hemopoietic pluripotent cells we have investigated the expression of telomerase activity in cultured human peripheral blood CD34+ cells, and CD34+ /CD117+ /CD13+ progenitor mast cells selected therefrom, with the idea that induction of telomerase is associated with clonal expansion of CD34+ /CD117+ /CD13+ cells. A rapid increase in telomerase activity preceded proliferation of both populations of cells in the presence of stem cell factor and either IL-3 or IL-6. The induction was transient, and telomerase activity declined to basal levels well before the appearance of mature mast cells. Studies with pharmacologic inhibitors suggested that this induction was initially dependent on the p38 mitogen-activated protein kinase and phosphatidylinositol 3'-kinase, but once cell replication was underway telomerase activity, but not cell replication, became resistant to the effects of inhibitors. Tumor mast cell lines, in contrast, expressed persistently high telomerase activity throughout the cell cycle, and this expression was unaffected by inhibitors of all known signaling pathways in mast cells even when cell proliferation was blocked for extended periods. These results suggest that the transient induction of telomerase activity in human progenitor mast cells was initially dependent on growth factor-mediated signals, whereas maintenance of high activity in tumor mast cell lines was not dependent on intracellular signals or cell replication.     

Sequencing and analysis of an Irish human genome

Background

Recent studies generating complete human sequences from Asian, African and European subgroups have revealed population-specific variation and disease susceptibility loci. Here, choosing a DNA sample from a population of interest due to its relative geographical isolation and genetic impact on further populations, we extend the above studies through the generation of 11-fold coverage of the first Irish human genome sequence.

Results

Using sequence data from a branch of the European ancestral tree as yet unsequenced, we identify variants that may be specific to this population. Through comparisons with HapMap and previous genetic association studies, we identified novel disease-associated variants, including a novel nonsense variant putatively associated with inflammatory bowel disease. We describe a novel method for improving SNP calling accuracy at low genome coverage using haplotype information. This analysis has implications for future re-sequencing studies and validates the imputation of Irish haplotypes using data from the current Human Genome Diversity Cell Line Panel (HGDP-CEPH). Finally, we identify gene duplication events as constituting significant targets of recent positive selection in the human lineage.

Conclusions

Our findings show that there remains utility in generating whole genome sequences to illustrate both general principles and reveal specific instances of human biology. With increasing access to low cost sequencing we would predict that even armed with the resources of a small research group a number of similar initiatives geared towards answering specific biological questions will emerge.     

Melanoma Differentiation-Associated Gene 5 (MDA5) Is Involved in the Innate Immune Response to Paramyxoviridae Infection In Vivo

The early host response to pathogens is mediated by several distinct pattern recognition receptors. Cytoplasmic RNA helicases including RIG-I and MDA5 have been shown to respond to viral RNA by inducing interferon (IFN) production. Previous in vitro studies have demonstrated a direct role for MDA5 in the response to members of the Picornaviridae, Flaviviridae and Caliciviridae virus families ((+) ssRNA viruses) but not to Paramyxoviridae or Orthomyxoviridae ((−) ssRNA viruses). Contrary to these findings, we now show that MDA5 responds critically to infections caused by Paramyxoviridae in vivo. Using an established model of natural Sendai virus (SeV) infection, we demonstrate that MDA5^−/− mice exhibit increased morbidity and mortality as well as severe histopathological changes in the lower airways in response to SeV. Moreover, analysis of viral propagation in the lungs of MDA5^−/− mice reveals enhanced replication and a distinct distribution involving the interstitium. Though the levels of antiviral cytokines were comparable early during SeV infection, type I, II, and III IFN mRNA expression profiles were significantly decreased in MDA5^−/− mice by day 5 post infection. Taken together, these findings indicate that MDA5 is indispensable for sustained expression of IFN in response to paramyxovirus infection and provide the first evidence of MDA5-dependent containment of in vivo infections caused by (−) sense RNA viruses.     

Integrated signalling pathways for mast-cell activation

Mast-cell activation mediated by the high-affinity receptor for IgE (FcepsilonRI) is considered to be a key event in the allergic inflammatory response. However, in a physiological setting, other receptors, such as KIT, might also markedly influence the release of mediators by mast cells. Recent studies have provided evidence that FcepsilonRI-dependent degranulation is regulated by two complementary signalling pathways, one of which activates phospholipase Cgamma and the other of which activates phosphatidylinositol 3-kinase, using specific transmembrane and cytosolic adaptor molecules. In this Review, we discuss the evidence for these interacting pathways and describe how the capacity of KIT, and other receptors, to influence FcepsilonRI-dependent mast-cell-mediator release might be a function of the relative abilities of these receptors to activate these alternative pathways.     

Serum inhibin A and B concentrations during the menstrual cycle in mothers of spontaneous dizygotic twins.

Dizygotic twinning in humans is influenced by genetic factors suggesting inherited variation affects follicle development and predisposes to double ovulations. In a previous study, we conducted a detailed examination of follicle development and variation in hormone concentrations during the menstrual cycle in mothers of DZ twins (MODZT) compared with an age-matched control group of mothers of singletons. We did not detect differences in FSH concentrations between mothers of twins and mothers of singletons. Serum inhibin concentrations were measured by a radioimmunoassay that did not distinguish between dimeric inhibin A and B forms and free inhibin alpha subunit. We therefore analyzed the samples from this study with specific assays to determine whether concentrations of inhibin A and B were different between MODZT and controls and therefore contribute to the twinning phenotype. There were no significant differences between MODZT with single ovulations and control women in inhibin A and B concentrations during the cycle, including the critical period for the selection of the dominant follicle. These data suggest that the genetic cause of twinning is not associated with changes in FSH concentrations or recognised feedback mechanisms regulating FSH release.     

Cutting edge: paradoxical roles of BST2/tetherin in promoting type I IFN response and viral infection

Bone marrow stromal Ag 2 (BST2) is a transmembrane protein that prevents virus release from infected cells. It was also reported that BST2 inhibits type I IFN production by plasmacytoid dendritic cells. To determine BST2 impact on antiviral responses in vivo, we generated BST2(-/-) mice. Following infection with a murine retrovirus, BST2(-/-) mice had slightly elevated viral loads; however, infection with other enveloped viruses revealed unexpected roles of BST2. BST2(-/-) mice showed reduced type I IFN production by plasmacytoid dendritic cells. Moreover, BST2(-/-) mice had lower viral titers in lungs following intranasal infection with vesicular stomatitis virus expressing OVA and influenza B and increased numbers of virus-specific CD8 T cells in the lungs, suggesting that BST2 may facilitate entry and/or replication of enveloped viruses and modulate priming of CD8 T cells. These findings suggest complex roles of BST2 beyond retroviral control in vivo, possibly reflecting the involvement of BST2 in endocytosis and intracellular trafficking of viruses, viral nucleic acids, and Ags.