A mouse model for Li-Fraumeni-Like Syndrome with cardiac angiosarcomas associated to POT1 mutations

The shelterin protein POT1 has been found mutated in many different familial and sporadic cancers, however, no mouse models to understand the pathobiology of these mutations have been developed so far. To address the molecular mechanisms underlying the tumorigenic effects of POT1 mutant proteins in humans, we have generated a mouse model for the human POT1^R117C mutation found in Li-Fraumeni-Like families with cases of cardiac angiosarcoma by introducing this mutation in the Pot1a endogenous locus, knock-in for Pot1a^R117C. We find here that both mouse embryonic fibroblasts (MEFs) and tissues from Pot1a^+/ki mice show longer telomeres than wild-type controls. Longer telomeres in Pot1a^+/ki MEFs are dependent on telomerase activity as they are not found in double mutant Pot1a^+/ki Tert^-/- telomerase-deficient MEFs. By using complementation assays we further show that POT1a pR117C exerts dominant-negative effects at telomeres. As in human Li-Fraumeni patients, heterozygous Pot1a^+/ki mice spontaneously develop a high incidence of angiosarcomas, including cardiac angiosarcomas, and this is associated to the presence of abnormally long telomeres in endothelial cells as well as in the tumors. The Pot1a^+/R117C mouse model constitutes a useful tool to understand human cancers initiated by POT1 mutations.     

Evidence for Geographic Isolation and Signs of Endemism within a Protistan Morphospecies

The possible existence of endemism among microorganisms resulting from and preserved by geographic isolation is one of the most controversial topics in microbial ecology. We isolated 31 strains of “Spumella-like” flagellates from remote sampling sites from all continents, including Antarctica. These and another 23 isolates from a former study were characterized morphologically and by small-subunit rRNA gene sequence analysis and tested for the maximum temperature tolerance. Only a minority of the Spumella morpho- and phylotypes from the geographically isolated Antarctic continent follow the worldwide trend of a linear correlation between ambient (air) temperature during strain isolation and heat tolerance of the isolates. A high percentage of the Antarctic isolates, but none of the isolates from locations on all other continents, were obligate psychrophilic, although some of the latter were isolated at low ambient temperatures. The drastic deviation of Antarctic representatives of Spumella from the global trend of temperature adaptation of this morphospecies provides strong evidence for geographic transport restriction of a microorganism; i.e., Antarctic protistan communities are less influenced by transport of protists to and from the Antarctic continent than by local adaptation, a subtle form of endemism.     

Limited overlapping roles of P15(INK4b) and P18(INK4c) cell cycle inhibitors in proliferation and tumorigenesis

Entry of quiescent cells into the cell cycle is driven by the cyclin D-dependent kinases Cdk4 and Cdk6. These kinases are negatively regulated by the INK4 cell cycle inhibitors. We report the generation of mice defective in P15(INK4b) and P18(INK4c). Ablation of these genes, either alone or in combination, does not abrogate cell contact inhibition or senescence of mouse embryo fibroblasts in culture. However, loss of P15(INK4b), but not of P18(INK4c), confers proliferative advantage to these cells and makes them more sensitive to transformation by H-ras oncogenes. In vivo, ablation of P15(INK4b) and P18(INK4c) genes results in lymphoproliferative disorders and tumor formation. Mice lacking P18(INK4c) have deregulated epithelial cell growth leading to the formation of cysts, mostly in the cortical region of the kidneys and the mammary epithelium. Loss of both P15(INK4b) and P18(INK4c) does not result in significantly distinct phenotypic manifestations except for the appearance of cysts in additional tissues. These results indicate that P15(INK4b) and P18(IKN4c) are tumor suppressor proteins that act in different cellular lineages and/or pathways with limited compensatory roles.     

Relationships between renal morphology and diet in 26 species of new world bats (suborder microchiroptera)

The renal morphology of 24 species of mormoopid and phyllostomid bats feeding on six different diets was examined to test evolutionary changes in several structural traits presumably led by dietary shifts from ancestral insectivorous diets. The kidneys of a fish-eating vespertilionid and an insect-eating emballonurid were also examined but not included in the phylogenetic comparison. The length, width, and breadth of the kidneys were used to calculate relative medullary thickness (RMT). Tissues were processed for stereological analysis, and the volumes of the kidney, nephron components, and vasculature were determined. RMT did not correlate with body mass in either animal-eating or plant-eating phyllostomid and mormoopid bats. The shift from insectivory to frugivory and nectarivory was accompanied by a reduction in RMT, a reduction in the percent of renal medulla, and an increase in the percent of renal cortex. No changes in these traits were observed in bats that shifted to carnivorous, omnivorous or sanguinivorous habits. No changes were observed in renal vasculature, in the percentage of cortical and medullary nephron components or of capillaries surrounding the nephrons in any feeding group. Vespertilionid and emballonurid species had similar values in all traits examined as compared to insectivorous phyllostomids and mormoopids. Our data suggest that diet does not influence a single area of the nephron, but rather the entire nephron such that the relative amounts of renal cortex and medulla are affected.     

Deep Crustal Communities of the Juan de Fuca Ridge Are Governed by Mineralogy

Volcanic ocean crust contains a global chemosynthetic microbial ecosystem that impacts ocean productivity, seawater chemistry and geochemical cycling. We examined the mineralogical effect on community structure in the aquifer ecosystem by using a four-year in situ colonization experiment with igneous minerals and glasses in Integrated Ocean Drilling Program Hole 1301A on the Juan de Fuca Ridge. Microbial community analysis and scanning electron microscopy revealed that olivine phases and iron-bearing minerals bore communities that were distinct from iron-poor phases. Communities were dominated by Archaeoglobaceae, Clostridia, Thermosipho, Desulforudis and OP1 lineages. Our results suggest that mineralogy determines microbial composition in the subseafloor aquifer ecosystem.     

ATM requirement in gene expression responses to ionizing radiation in human lymphoblasts and fibroblasts

The heritable disorder ataxia telangiectasia (AT) is caused by mutations in the AT-mutated (ATM) gene with manifestations that include predisposition to lymphoproliferative cancers and hypersensitivity to ionizing radiation (IR). We investigated gene expression changes in response to IR in human lymphoblasts and fibroblasts from seven normal and seven AT-affected individuals. Both cell types displayed ATM-dependent gene expression changes after IR, with some responses shared and some responses varying with cell type and dose. Interestingly, after 5 Gy IR, lymphoblasts displayed ATM-independent responses not seen in the fibroblasts at this dose, which likely reflect signaling through ATM-related kinases, e.g., ATR, in the absence of ATM function.     

A strictly anaerobic betaproteobacterium Georgfuchsia toluolica gen. nov., sp. nov. degrades aromatic compounds with Fe(III), Mn(IV) or nitrate as an electron acceptor

A bacterium (strain G5G6) that grows anaerobically with toluene was isolated from a polluted aquifer (Banisveld, the Netherlands). The bacterium uses Fe(III), Mn(IV) and nitrate as terminal electron acceptors for growth on aromatic compounds. The bacterium does not grow on sugars, lactate or acetate. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain G5G6 belonged to the Betaproteobacteria . Its closest, but only distantly related, cultured relative is Sterolibacterium denitrificans Chol-1S^T (94.6% similarity of the 16S rRNA genes), a cholesterol-oxidizing, denitrifying bacterium. Strain G5G6 possesses the benzylsuccinate synthase A ( bssA ) gene encoding the α-subunit of Bss, which catalyzes the first step in anaerobic toluene degradation. The deduced BssA amino acid sequence is closely related to those of Azoarcus and Thauera species, which also belong to the Betaproteobacteria . Strain G5G6 is the first toluene-degrading, iron-reducing bacterium that does not belong to the Geobacteraceae within the Deltaproteobacteria . Based on phylogenetic and physiological comparison, strain G5G6 could not be assigned to a described species. Therefore, strain G5G6 (DSMZ 19032^T=JCM 14632^T) is a novel taxon of the Betaproteobacteria . We propose the name Georgfuchsia toluolica gen. nov., sp. nov.