The effect of elevation on the distribution of sibling species in the Simulium arcticum complex (Diptera: Simuliidae)

At least 5 sibling species and an additional 11 cytotypes of the Simulium arcticum complex occur in Montana. Consequently, this speciose complex might allow study of environmental correlates with genetic differentiation. We used conventional methods of collection and cytogenetic analysis to study 1128 male larvae of the Simulium arcticum complex at 15 sites within 5 drainages in western Montana to test the hypothesis that distribution of siblings is associated with elevation. We sampled at the mouth, at the headwaters, and at an intermediate site to span the range of elevations within each drainage. We restricted our analyses to the most abundant taxa of the S. arcticum complex within our study area and observed a statistically significant presence of S. apricarium at low-elevation sites. Simulium arcticum IIL-18 appeared more frequently than expected at high elevation sites. Simulium brevicercum and S. arcticum sensu strictu appeared to be distributed randomly. We suggest potential causal reasons for these distributions including differential use of habitats along these elevational gradients.     

The fungal glutathione S-transferase system. Evidence of new classes in the wood-degrading basidiomycete Phanerochaete chrysosporium

The recent release of several basidiomycete genome sequences allows an improvement of the classification of fungal glutathione S-transferases (GSTs). GSTs are well-known detoxification enzymes which can catalyze the conjugation of glutathione to non-polar compounds that contain an electrophilic carbon, nitrogen, or sulfur atom. Following this mechanism, they are able to metabolize drugs, pesticides, and many other xenobiotics and peroxides. A genomic and phylogenetic analysis of GST classes in various sequenced fungi—zygomycetes, ascomycetes, and basidiomycetes—revealed some particularities in GST distribution, in comparison with previous analyses with ascomycetes only. By focusing essentially on the wood-degrading basidiomycete Phanerochaete chrysosporium, this analysis highlighted a new fungal GST class named GTE, which is related to bacterial etherases, and two new subclasses of the omega class GSTs. Moreover, our phylogenetic analysis suggests a relationship between the saprophytic behavior of some fungi and the number and distribution of some GST isoforms within specific classes.     

Changes to cellular water and element content induced by nucleolar stress: investigation by a cryo-correlative nano-imaging approach

The cell is a crowded volume, with estimated mean mass percentage of macromolecules and of water ranging from 7.5 to 45 and 55 to 92.5 %, respectively. However, the concentrations of macromolecules and water at the nanoscale within the various cell compartments are unknown. We recently developed a new approach, correlative cryo-analytical scanning transmission electron microscopy, for mapping the quantity of water within compartments previously shown to display GFP-tagged protein fluorescence on the same ultrathin cryosection. Using energy-dispersive X-ray spectrometry (EDXS), we then identified various elements (C, N, O, P, S, K, Cl, Mg) in these compartments and quantified them in mmol/l. Here, we used this new approach to quantify water and elements in the cytosol, mitochondria, condensed chromatin, nucleoplasm, and nucleolar components of control and stressed cancerous cells. The water content of the control cells was between 60 and 83 % (in the mitochondria and nucleolar fibrillar centers, respectively). Potassium was present at concentrations of 128–462 mmol/l in nucleolar fibrillar centers and condensed chromatin, respectively. The induction of nucleolar stress by treatment with a low dose of actinomycin-D to inhibit rRNA synthesis resulted in both an increase in water content and a decrease in the elements content in all cell compartments. We generated a nanoscale map of water and elements within the cell compartments, providing insight into their changes induced by nucleolar stress.     

Role of genomic instability and p53 in AID-induced c-myc-Igh translocations

Chromosomal translocations involving the immunoglobulin switch region are a hallmark feature of B-cell malignancies. However, little is known about the molecular mechanism by which primary B cells acquire or guard against these lesions. Here we find that translocations between c-myc and the IgH locus (Igh) are induced in primary B cells within hours of expression of the catalytically active form of activation-induced cytidine deaminase (AID), an enzyme that deaminates cytosine to produce uracil in DNA. Translocation also requires uracil DNA glycosylase (UNG), which removes uracil from DNA to create abasic sites that are then processed to double-strand breaks. The pathway that mediates aberrant joining of c-myc and Igh differs from intrachromosomal repair during immunoglobulin class switch recombination in that it does not require histone H2AX, p53 binding protein 1 (53BP1) or the non-homologous end-joining protein Ku80. In addition, translocations are inhibited by the tumour suppressors ATM, Nbs1, p19 (Arf) and p53, which is consistent with activation of DNA damage- and oncogenic stress-induced checkpoints during physiological class switching. Finally, we demonstrate that accumulation of AID-dependent, IgH-associated chromosomal lesions is not sufficient to enhance c-myc-Igh translocations. Our findings reveal a pathway for surveillance and protection against AID-dependent DNA damage, leading to chromosomal translocations.     

Expression of tumour-specific antigens underlies cancer immunoediting

Cancer immunoediting is a process by which immune cells, particularly lymphocytes of the adaptive immune system, protect the host from the development of cancer and alter tumour progression by driving the outgrowth of tumour cells with decreased sensitivity to immune attack. Carcinogen-induced mouse models of cancer have shown that primary tumour susceptibility is thereby enhanced in immune-compromised mice, whereas the capacity for such tumours to grow after transplantation into wild-type mice is reduced. However, many questions about the process of cancer immunoediting remain unanswered, in part because of the known antigenic complexity and heterogeneity of carcinogen-induced tumours. Here we adapted a genetically engineered, autochthonous mouse model of sarcomagenesis to investigate the process of cancer immunoediting. This system allows us to monitor the onset and growth of immunogenic and non-immunogenic tumours induced in situ that harbour identical genetic and histopathological characteristics. By comparing the development of such tumours in immune-competent mice with their development in mice with broad immunodeficiency or specific antigenic tolerance, we show that recognition of tumour-specific antigens by lymphocytes is critical for immunoediting against sarcomas. Furthermore, primary sarcomas were edited to become less immunogenic through the selective outgrowth of cells that were able to escape T lymphocyte attack. Loss of tumour antigen expression or presentation on major histocompatibility complex I was necessary and sufficient for this immunoediting process to occur. These results highlight the importance of tumour-specific-antigen expression in immune surveillance, and potentially, immunotherapy.