E versus Z geometry in β-d-arabino-hexopyranosidulose oximes

Koenigs–Knorr-type glycosidations of peracylated 2Z-benzoyloxyimino-glycopyranosyl bromides invariably proceed with retention of the Z-geometry. Accordingly, the many β-d-hexosidulose oximes in literature which were prepared in this way and for which the oxime geometry has not been addressed explicitly, are the Z-oximes throughout. By contrast, oximation of β-d-hexopyranosid-2-uloses leads to mixtures of E and Z oximes readily separable and structurally verifiable by ¹H and ¹³C NMR. Configurational assignments rested on comparative evaluation of NMR data of E and Z isomers, and, most notably on an X-ray structural analysis of the pivaloylated isopropyl 2E-benzoyloxyimino-2-deoxy-β-d-arabino-hexopyranoside revealing the unusual ¹S₅^1,4B conformation for the pyranoid ring.     

Heterogeneity of mouse primordial germ cells reflecting the distinct status of their differentiation, proliferation and apoptosis can be classified by the expression of cell surface proteins integrin α6 and c-Kit

Primordial germ cells (PGCs) in mouse embryos likely include heterogeneous cells having distinct cellular properties. In the present study, we found that heterogeneity of PGCs can be defined by the expression of integrin α6 and c-Kit. The changes in integrin α6 and c-Kit expression in PGCs were obvious as embryonic development progressed, and the PGCs became a mixture of populations consisting of cells with distinct levels of cell surface protein expression. The changes and heterogeneity of cell surface protein expression mainly reflected asynchronous differentiation of PGCs. Apoptosis of PGCs was biased in populations of c-Kit or integrin α6 negative PGCs at particular developmental stages, suggesting possible linkage between PGC apoptosis and the levels of expression of these cell surface proteins. Histochemical analysis confirmed the heterogeneous expression of c-Kit and integrin α6 in PGCs in embryonic gonads, and revealed that PGCs showing different levels of integrin α6 or c-Kit expression and the apoptotic PGCs were scattered and did not show specific localization within gonads. The present study enables us to analyze and isolate populations of living PGCs showing a distinct status of differentiation, or different properties of proliferation or of cell death in individual embryos, and provides a new strategy to examine the mechanisms of PGC development.     

POLLINATOR-MEDIATED SELECTION ON FLORAL DISPLAY AND FLOWERING TIME IN THE PERENNIAL HERB ARABIDOPSIS LYRATA

The evolution of floral display and flowering time in animal-pollinated plants is commonly attributed to pollinator-mediated selection. Yet, the causes of selection on flowering phenology and traits contributing to floral display have rarely been tested experimentally in natural populations. We quantified phenotypic selection on morphological and phenological characters in the perennial, outcrossing herb Arabidopsis lyrata in two years using female reproductive success as a proxy of fitness. To determine whether selection on floral display and flowering phenology can be attributed to interactions with pollinators, selection was quantified both for open-pollinated controls and for plants receiving supplemental hand-pollination. We documented directional selection for many flowers, large petals, late start of flowering, and early end of flowering. Seed output was pollen-limited in both years and supplemental hand-pollination reduced the magnitude of selection on number of flowers, and reversed the direction of selection on end of flowering. The results demonstrate that interactions with pollinators may affect the strength of selection on floral display and the direction of selection on phenology of flowering in natural plant populations. They thus support the contention that pollinators can drive the evolution of both floral display and flowering time.     

Plasmodium yoelii: Adverse outcome of non-lethal P. yoelii malaria during co-infection with Schistosoma mansoni in BALB/c mouse model

Plasmodium yoelii and Schistosoma mansoni co-infections were studied in female BALB/c mice aged 4-6 weeks to determine the effect of time and stage of concomitant infections on malaria disease outcome. Patent S. mansoni infection in BALB/c mice increased malaria peak parasitemia and caused death from an otherwise non-lethal, self-resolving P. yoelii malaria infection. Exacerbation of malaria parasitemia occurred during both pre-patent and patent S. mansoni infection resulting in a delay of 4-8 days in malaria parasite resolution in co-infected mice. Praziquantel administered to mice with patent schistosome infection protected from fatal outcome during co-infection. However, this treatment did not completely clear the worm infestation, nor did it reduce the peak malaria parasitemia reached, which was nonetheless resolved completely. Hepatosplenomegaly was more marked in schistosome and malaria co-infected mice compared to either infection separately. The results suggest a complex relationship between schistosome co-infection and malaria disease outcome in which the timing of malaria infection in relation to schistosome acquisition is critical to disease outcome and pathology.     

Identification of the putative tumor suppressor Nit2 as ω-amidase, an enzyme metabolically linked to glutamine and asparagine transamination

The present report identifies the enzymatic substrates of a member of the mammalian nitrilase-like (Nit) family. Nit2, which is widely distributed in nature, has been suggested to be a tumor suppressor protein. The protein was assumed to be an amidase based on sequence homology to other amidases and on the presence of a putative amidase-like active site. This assumption was recently confirmed by the publication of the crystal structure of mouse Nit2. However, the in vivo substrates were not previously identified. Here we report that rat liver Nit2 is ω-amidodicarboxylate amidohydrolase (E.C. 3.5.1.3; abbreviated ω-amidase), a ubiquitously expressed enzyme that catalyzes a variety of amidase, transamidase, esterase and transesterification reactions. The in vivo amidase substrates are α-ketoglutaramate and α-ketosuccinamate, generated by transamination of glutamine and asparagine, respectively. Glutamine transaminases serve to salvage a number of α-keto acids generated through non-specific transamination reactions (particularly those of the essential amino acids). Asparagine transamination appears to be useful in mitochondrial metabolism and in photorespiration. Glutamine transaminases play a particularly important role in transaminating α-keto-γ-methiolbutyrate, a key component of the methionine salvage pathway. Some evidence suggests that excess α-ketoglutaramate may be neurotoxic. Moreover, α-ketosuccinamate is unstable and is readily converted to a number of hetero-aromatic compounds that may be toxic. Thus, an important role of ω-amidase is to remove potentially toxic intermediates by converting α-ketoglutaramate and α-ketosuccinamate to biologically useful α-ketoglutarate and oxaloacetate, respectively. Despite its importance in nitrogen and sulfur metabolism, the biochemical significance of ω-amidase has been largely overlooked. Our report may provide clues regarding the nature of the biological amidase substrate(s) of Nit1 (another member of the Nit family), which is a well-established tumor suppressor protein), and emphasizes a) the crucial role of Nit2 in nitrogen and sulfur metabolism, and b) the possible link of Nit2 to cancer biology.     

In silico study of kinetochore control, amplification, and inhibition effects in MCC assembly

Eukaryotic cells rely on a surveillance mechanism, the "Spindle Assembly Checkpoint"SACM in order to ensure accurate chromosome segregation by preventing anaphase initiation until all chromosomes are correctly attached to the mitotic spindle. In different organisms, a mitotic checkpoint complex (MCC) composed of Mad2, Bub3, BubR1/Mad3, and Cdc20 inhibits the anaphase promoting complex (APC/C) to initiate promotion into anaphase. The mechanism of MCC formation and its regulation by the kinetochore are unclear. Here, we constructed dynamical models of MCC formation involving different kinetochore control mechanisms including amplification as well as inhibition effects, and analysed their quantitative properties. In particular, in this system, fast and stable metaphase to anaphase transition can only be triggered when the kinetochore controls the Bub3:BubR1-related reactions; signal amplification and inhibition play a subordinate role. Furthermore, when introducing experimentally determined parameter values into the models analysed here, we found that effective MCC formation is not combined with complete Cdc20 sequestering. Instead, the MCC might bind and completely block the APC/C. The SACM might function by an MCC:APC/C complex rearrangement.     

36° step size of proton‐driven c‐ring rotation in FoF1‐ATP synthase

Synthesis of adenosine triphosphate ATP, the ‘biological energy currency’, is accomplished by F_oF₁‐ATP synthase. In the plasma membrane of Escherichia coli, proton‐driven rotation of a ring of 10 c subunits in the F_o motor powers catalysis in the F₁ motor. Although F₁ uses 120° stepping during ATP synthesis, models of F_o predict either an incremental rotation of c subunits in 36° steps or larger step sizes comprising several fast substeps. Using single‐molecule fluorescence resonance energy transfer, we provide the first experimental determination of a 36° sequential stepping mode of the c‐ring during ATP synthesis.     

QTL for resistance to Salmonella carrier state confirmed in both experimental and commercial chicken lines

The ability of chickens to carry Salmonella without displaying disease symptoms is responsible for Salmonella propagation in poultry stocks and for subsequent human contamination through the consumption of contaminated eggs or meat. The selection of animals more resistant to carrier state might be a way to decrease the propagation of Salmonella in poultry stocks and its transmission to humans. Five QTL controlling variation for resistance to carrier state in a chicken F₂ progeny derived from the White Leghorn inbred lines N and 6₁ had been previously identified using a selective genotyping approach. Here, a second analysis on the whole progeny was performed, which led to the confirmation of two QTL on chromosomes 2 and 16. To assess the utility of these genomic regions for selection in commercial lines, we tested them together with other QTL identified in an [N×6₁] × N backcross progeny and with the candidate genes SLC11A1 and TLR4 . We used a commercial line divergently selected for either low or high carrier-state resistance both in young chicks and in adult hens. In divergent chick lines, one QTL on chromosome 1 and one in the SLC11A1 region were significantly associated with carrier-state resistance variations; in divergent adult lines, one QTL located in the major histocompatibility complex on chromosome 16 and one in the SLC11A1 region were involved in these variations. Genetic studies conducted on experimental lines can therefore be of potential interest for marker-assisted selection in commercial lines.