Dissecting the transcriptional phenotype of ribosomal protein deficiency: implications for Diamond-Blackfan Anemia

Defects in genes encoding ribosomal proteins cause Diamond Blackfan Anemia (DBA), a red cell aplasia often associated with physical abnormalities. Other bone marrow failure syndromes have been attributed to defects in ribosomal components but the link between erythropoiesis and the ribosome remains to be fully defined. Several lines of evidence suggest that defects in ribosome synthesis lead to “ribosomal stress” with p53 activation and either cell cycle arrest or induction of apoptosis. Pathways independent of p53 have also been proposed to play a role in DBA pathogenesis.     

Expression profile of nuclear receptors along male mouse nephron segments reveals a link between ERRβ and thick ascending limb function

The nuclear receptor family orchestrates many functions related to reproduction, development, metabolism, and adaptation to the circadian cycle. The majority of these receptors are expressed in the kidney, but their exact quantitative localization in this ultrastructured organ remains poorly described, making it difficult to elucidate the renal function of these receptors. In this report, using quantitative PCR on microdissected mouse renal tubules, we established a detailed quantitative expression map of nuclear receptors along the nephron. This map can serve to identify nuclear receptors with specific localization. Thus, we unexpectedly found that the estrogen-related receptor β (ERRβ) is expressed predominantly in the thick ascending limb (TAL) and, to a much lesser extent, in the distal convoluted tubules. In vivo treatment with an ERR inverse agonist (diethylstilbestrol) showed a link between this receptor family and the expression of the Na⁺,K⁺-2Cl⁻ cotransporter type 2 (NKCC2), and resulted in phenotype presenting some similarities with the Bartter syndrom (hypokalemia, urinary Na⁺ loss and volume contraction). Conversely, stimulation of ERRβ with a selective agonist (GSK4716) in a TAL cell line stimulated NKCC2 expression. All together, these results provide broad information regarding the renal expression of all members of the nuclear receptor family and have allowed us to identify a new regulator of ion transport in the TAL segments.     

Opsonin-dependent phagocytosis of bacteria by murine macrophage-like cells

We have investigated the phagocytic properties of the macrophage-like cell line DCH-7, derived from fusion of mouse macrophages with a mouse T-lymphoma cell line. These cells phagocytosed opsonized bacteria. IgG appeared to be the major opsonin forStaphylococcus aureus Wood 46 as well as for threeEscherichia coli strains; complement components were not required as opsonins. Intracellular bacteria survived to a large extent. This model system should be a useful tool for studying the process of phagocytosis and phagocytic killing of bacteria.     

Pro-oxidant mitochondrial matrix-targeted ubiquinone MitoQ10 acts as anti-oxidant at retarded electron transport or proton pumping within Complex I

Oxidative stress of mitochondrial origin, i.e. elevated mitochondrial superoxide production, belongs to major factors determining aging and oxidative-stress-related diseases. Antioxidants, such as the mitochondria-targeted coenzyme Q, MitoQ₁₀, may prevent or cure these pathological conditions. To elucidate pro- and anti-oxidant action of MitoQ₁₀, we studied its effects on HepG2 cell respiration, mitochondrial network morphology, and rates of superoxide release (above that neutralized by superoxide dismutase) to the mitochondrial matrix (J_m). MitoSOX Red fluorescence confocal microscopy monitoring of J_m rates showed pro-oxidant effects of 3.5-fold increased J_m with MitoQ₁₀. MitoQ₁₀ induced fission of the mitochondrial network which was recovered after 24 h. In rotenone-inhibited HepG2 cells (i.e., already under oxidative stress) MitoQ₁₀ sharply decreased rotenone-induced J_m, but not together with the Complex II inhibitor thenoyltrifluoroacetone. Respiration of HepG2 cells and isolated rat liver mitochondria with MitoQ₁₀ increased independently of rotenone. The increase was prevented by thenoyltrifluoroacetone. These results suggest that MitoQ₁₀ accepts electrons prior to the rotenone-bound Q-site, and the Complex II reverse mode oxidizes MitoQ₁₀H₂ to regenerate MitoQ₁₀. Consequently, MitoQ₁₀ has a pro-oxidant role in intact cells, whereas it serves as an antioxidant when Complex I-derived superoxide generation is already elevated due to electron flow retardation. Moreover, unlike mitochondrial uncoupling, MitoQ₁₀ exerted its antioxidant role when Complex I proton pumping was retarded by a hydrophobic amiloride, 5-(N-ethyl-N-isopropyl) amiloride. Consequently, MitoQ₁₀ may be useful in the treatment of diseases originating from impairment of respiratory chain Complex I due to oxidatively damaged mitochondrial DNA, when its targeted delivery to pathogenic tissues is ensured.     

Synthesis and in vitro activities of ferrocenic aminohydroxynaphthoquinones against Toxoplasma gondii and Plasmodium falciparum

Fourteen ferrocenyl aminohydroxynaphthoquinones, analogues of atovaquone, were synthesized from the hydroxynaphthoquinone core. These novel atovaquone derivatives were tested for their in vitro activity against two apicomplexan parasites of medical importance, Toxoplasma gondii and Plasmodium falciparum, including resistant strains to atovaquone (T. gondii) and chloroquine (P. falciparum). Three of these ferrocenic atovaquone derivatives composed of the hydroxynaphthoquinone core plus an amino-ferrocenic group and an aliphatic chain with 6-8 carbon atoms were found to be significantly active against T. gondii. Moreover, these novel compounds were also effective against the atovaquone-resistant strain of T. gondii (Ato(R)).     

Fuel economy,woodland management and adaptation strategies in a Classic Maya city: applying anthracology to urban settings in high biodiversity tropical forests

Vegetation History and Archaeobotany - Fuelling ancient Maya cities and industries has been identified for some time now as a critical concern for the pre-Columbian Maya, especially since there is...     

The contribution of the cell wall to a transmembrane calcium gradient could play a key role in Bacillus subtilis protein secretion

A weak Ca²⁺-binding site (K_a= 0.8× 10³ M^?1, at pH7) was identified in the mature part of levansucrase. An amino acid substitution (Thr-236 →lle) in this site alters simultaneously the affinity for calcium, the folding transition and the efficiency of the secretion process of levansucrase. Moreover, the ability of the Bacillus subtilis cell wall to concentrate calcium ions present in the culture medium was studied. We confirm the results of Beveridge and Murray who showed that the concentration factor is about 100 to 120 times. This property preserves a high concentration of Ca²⁺ (>2 mM) on the external side of the cytoplasmic membrane, even in the absence of further Ca2+ supplementation in the growth medium. Such local conditions allow the spontaneous unfolding folding transition of levansucrase en route for secretion. Since several exocellular proteins of B. subtilis are calcium-binding proteins, we propose that the high concentration of calcium ion in the microenvironment of the cell wall may play a key role in the ultimate step of their secretion process.     

Stable Isotope and Signature Fatty Acid Analyses Suggest Reef Manta Rays Feed on Demersal Zooplankton

Assessing the trophic role and interaction of an animal is key to understanding its general ecology and dynamics. Conventional techniques used to elucidate diet, such as stomach content analysis, are not suitable for large threatened marine species. Non-lethal sampling combined with biochemical methods provides a practical alternative for investigating the feeding ecology of these species. Stable isotope and signature fatty acid analyses of muscle tissue were used for the first time to examine assimilated diet of the reef manta ray Manta alfredi, and were compared with different zooplankton functional groups (i.e. near-surface zooplankton collected during manta ray feeding events and non-feeding periods, epipelagic zooplankton, demersal zooplankton and several different zooplankton taxa). Stable isotope δ¹⁵N values confirmed that the reef manta ray is a secondary consumer. This species had relatively high levels of docosahexaenoic acid (DHA) indicating a flagellate-based food source in the diet, which likely reflects feeding on DHA-rich near-surface and epipelagic zooplankton. However, high levels of ω6 polyunsaturated fatty acids and slightly enriched δ¹³C values in reef manta ray tissue suggest that they do not feed solely on pelagic zooplankton, but rather obtain part of their diet from another origin. The closest match was with demersal zooplankton, suggesting it is an important component of the reef manta ray diet. The ability to feed on demersal zooplankton is likely linked to the horizontal and vertical movement patterns of this giant planktivore. These new insights into the habitat use and feeding ecology of the reef manta ray will assist in the effective evaluation of its conservation needs.