Larval density affects phenotype and surrounding bacterial community without altering gut microbiota in Drosophila melanogaster

Larval crowding represents a complex stressful situation arising from inter-individual competition for time- and space-limited resources. The foraging of a large number of individuals may alter the chemical and bacterial composition of food and in turn affect individual's traits. Here we used Drosophila melanogaster to explore these assumptions. First, we used a wide larval density gradient to investigate the impact of crowding on phenotypical traits. We confirmed that high densities increased development time and pupation height, and decreased viability and body mass. Next, we measured concentrations of common metabolic wastes (ammonia, uric acid) and characterized bacterial communities, both in food and in larvae, for three contrasting larval densities (low, medium and high). Ammonia concentration increased in food from medium and high larval densities, but remained low in larvae regardless of the larval density. Uric acid did not accumulate in food but was detected in larvae. Surprisingly, bacterial composition remained stable in guts of larvae whatever their rearing density, although it drastically changed in the food. Overall, these results indicate that crowding deeply affects individuals, and also their abiotic and biotic surroundings. Environmental bacterial communities likely adapt to altered nutritional situations resulting from crowding, putatively acting as scavengers of larval metabolic wastes.

Evidence of a permanent electric polarisation in highly strained Cr2O3 clusters measured by a second harmonic generation technique

We investigate the second harmonic generation (SHG) signal in strained Cr₂O₃ clusters. We show that the SHG signal generated by nanometric Cr₂O₃ clusters embedded in MgO varies under an applied electric field, at room temperature. The variation of the intensity follows a Langevin law as a function of the electric field, which is consistent with a super-paraelectric clusters assembly. This reveals the presence of a weak spontaneous electric dipole in Cr₂O₃ when in the shape of highly strained epitaxial clusters, whereas this material does not posses any permanent electric dipole in the bulk phase. These results indicate that the multiferroic state recently observed at low temperature in those clusters, which was associated to a giant magneto-electric effect, might still exist at room temperature: this opens the way to new applications based on chromium oxide strained nanoparticles.

Combined effect of temperature and ammonia on molecular response and survival of the freshwater crustacean Gammarus pulex

Freshwater ecosystems are experiencing mounting pressures from agriculture, urbanization, and climate change, which could drastically impair aquatic biodiversity. As nutrient inputs increase and temperatures rise, ammonia (NH₃) concentration is likely to be associated with stressful temperatures. To investigate the interaction between NH₃ and temperature on aquatic invertebrate survival, we performed a factorial experiment on the survival and molecular response of Gammarus pulex, with temperature (10, 15, 20, and 25°C) and NH₃ (0, 0.5, 1, 2, 3, and 4mg NH₃/L) treatments. We observed an unexpected antagonistic interaction between temperature and NH₃ concentration, meaning survival in the 4mg NH₃/L treatment was higher at 25°C than at the control temperature of 10°C. A toxicokinetic-toxicodynamic (TK-TD) model was built to describe this antagonistic interaction. While the No Effect Concentration showed no significant variation across temperatures, the 50% lethal concentration at the end of the experiment increased from 2.7 (2.1-3.6) at 10°C to 5.5 (3.5- 23.4) mg NH₃/L at 25°C. Based on qPCR data, we associated these survival patterns to variations in the expression of the hsp70 gene, a generic biomarker of stress. However, though there was a 14-fold increase in hsp70 mRNA expression for gammarids exposed to 25°C compared to controls, NH₃ concentration had no effect on hsp70 mRNA synthesis across temperatures. Our results demonstrate that the effects of combined environmental stressors, like temperature and NH₃, may strongly differ from simple additive effects, and that stress response to temperature can actually increase resilience to nutrient pollution in some circumstances.

Dual effects of α2 -adrenoceptors in modulating myogenic tone in sheep isolated internal anal sphincter

BACKGROUND

The role of α-adrenoceptors in promoting continence through modulation of sphincter tone has focused primarily on the effects of α1 -adrenoceptors. We have used three clinically available agents, which are selective for α2 -adrenoceptors, to investigate their role in contractile and neurogenic responses on the internal anal sphincter (IAS).

METHODS

IAS strips, which had spontaneously generated tone, were used to investigate the contractile effect of lofexidine, brimonidine, and dexmedetomidine on muscle tone in the presence or absence of subtype selective antagonists. The effect of brimonidine on the magnitude and time course of neurogenic responses generated by electrical field stimulation (EFS) was also examined. The affinity of test compounds at α1 - and α2 -adrenoceptors was established by competition binding with [3H]-prazosin and [3H]-RX821002.

KEY RESULTS

All agonists caused concentration-dependent contraction of the IAS and lofexidine demonstrated an enantiomeric difference in potency with a 10-fold difference between the (-) and (+) isomers. Responses to lofexidine and dexmedetomidine were inhibited in the presence of the α1 -adrenoceptor selective antagonist prazosin, but not in the presence of RX811059 (α2 -adrenoceptor selective antagonist); brimonidine responses were inhibited by RX811059 and, to a lesser extent, by prazosin. Brimonidine affected both magnitude and duration of neurogenic responses, which was reversed in the presence of RX811059.

CONCLUSIONS & INFERENCES

We conclude that α2 -adrenoceptors can mediate contraction of IAS, although this effect is most evident with efficacious imidazoline agonists rather than the most selective ligand. In addition, this receptor subtype can directly inhibit noradrenergic contractile responses to EFS and, indirectly, enhance nitrergic relaxatory responses.

Size-induced enhanced magnetoelectric effect and multiferroicity in chromium oxide nanoclusters

The control of the magnetization of a material with an electric field would make the design and the integration of novel electronic devices possible. This explains the renewed interest in multiferroic materials. Progress in this field is currently hampered by the scarcity of the materials available and the smallness of the magnetoelectric effects. Here we present a proof-of-principle experiment showing that engineering large strains through nanoscale size reduction is an efficient route for increasing magnetoelectric coefficients by orders of magnitude. The archetype magnetoelectric material, Cr2O3, in the form of epitaxial clusters, exhibits an unprecedented 600% change in magnetization magnitude under 1 V. Furthermore, a multiferroic phase, with both magnetic and electric spontaneous polarizations, is found in the clusters, while absent in the bulk.

Induction of haploid and diploid plants though in vitro anther culture of haploid wheat (n=3x=21)

Five haploid plants of wheat were used for anther culture. Embryos were formed and six plants were regenerated. Of these, two were haploid (n=3x=21) and two diploid (2n=6x=42). The two diploids derived from the anthers of the same haploid wheat plant gave seeds, but the fertility was reduced in one of them showing, abnormalities at meiosis.

Investigation of the distribution and function of alpha-adrenoceptors in the sheep isolated internal anal sphincter

BACKGROUND AND PURPOSE

We have investigated the distribution of alpha-adrenoceptors in sheep internal anal sphincter (IAS), as a model for the human tissue, and evaluated various imidazoline derivatives for potential treatment of faecal incontinence.

EXPERIMENTAL APPROACH

Saturation and competition binding with (3)H-prazosin and (3)H-RX821002 were used to confirm the presence and density of alpha-adrenoceptors in sheep IAS, and the affinity of imidazoline compounds at these receptors. A combination of in vitro receptor autoradiography and immunohistochemistry was used to investigate the regional distribution of binding sites. Contractile activity of imidazoline-based compounds on sheep IAS was assessed by isometric tension recording.

KEY RESULTS

Saturation binding confirmed the presence of both alpha(1)- and alpha(2)-adrenoceptors, and subsequent characterization with sub-type-selective agents, identified them as alpha(1A)- and alpha(2D)-adrenoceptor sub-types. Autoradiographic studies with (3)H-prazosin showed a positive association of alpha(1)-adrenoceptors with immunohistochemically identified smooth muscle fibres. Anti-alpha(1)-adrenoceptor immunohistochemistry revealed similar distributions of the receptor in sheep and human IAS. The imidazoline compounds caused concentration-dependent contractions of the anal sphincter, but the maximum responses were less than those elicited by l-erythro-methoxamine, a standard non-imidazoline alpha(1)-adrenoceptor agonist. Prazosin (selective alpha(1)-adrenoceptor antagonist) significantly reduced the magnitude of contraction to l-erythro-methoxamine at the highest concentration used. Both prazosin and RX811059 (a selective alpha(2)-adrenoceptor antagonist) reduced the potency (pEC(50)) of clonidine.

CONCLUSIONS AND IMPLICATIONS

This study shows that both alpha(1)- and alpha(2)-adrenoceptors are expressed in the sheep IAS, and contribute (perhaps synergistically) to contractions elicited by various imidazoline derivatives. These agents may prove useful in the treatment of faecal incontinence.

Training effect in an exchange bias system: the role of interfacial domain walls

Polarized neutron reflectivity (PNR) is used to obtain the magnetic depth profile of an antiferromagnetically coupled ferrimagnetic/ferrimagnetic bilayer, Gd40Fe60/Tb12Fe88. This system shows a transition from positive to negative exchange bias field H(E) as the cooling field H(cf) is increased from small to large positive value. It also exhibits training behavior upon field cycling which affects H(E) and the coercive field H(C). From the PNR measurements at room temperature and at 15 K, we confirm that the magnetic configuration inside the TbFe layer is frozen when the sample is cooled in various H(cf). The thickness and pitch of the magnetic twist inside the TbFe layer depend on H(cf) and give rise to the observed differences in the bias field. Irreversible reorganization of the TbFe magnetization at the interface occurs upon GdFe magnetization reversal and is found to explain the training effect as well as the overall reduction in coercivity.

Arabidopsis kinome: after the casting

Arabidopsis thaliana is used as a favourite experimental organism for many aspects of plant biology. We capitalized on the recently available Arabidopsis genome sequence and predicted proteome, to draw up a genome-scale protein serine/threonine kinase (PSTK) inventory. The PSTKs represent about 4% of the A. thaliana proteome. In this study, we provide a description of the content and diversity of the non-receptor PSTKs. These kinases have crucial functions in sensing, mediating and coordinating cellular responses to an extensive range of stimuli. A total of 369 predicted non receptor PSTKs were detailed: the Raf superfamily, the CMGC, CaMK, AGC and STE families, as well as a few small clades and orphan sequences. An extensive relationship analysis of these kinases allows us to classify the proteins in superfamilies, families, sub-families and groups. The classification provides a better knowledge of the characteristics shared by the different clades. We focused on the MAP kinase module elements, with particular attention to their docking sites for protein-protein interaction and their biological function. The large number of A. thaliana genes encoding kinases might have been achieved through successive rounds of gene and genome duplications. The evolution towards an increasing gene number suggests that functional redundancy plays an important role in plant genetic robustness.

Foreign gene delivery into monocotyledonous species

Monocotyledonous plants are generally more recalcitrant to genetic transformation than dicotyledonous species. The absence of reliable Agrobacterium-mediated transformation methods and the difficulties associated with the culture of monocotyledonous tissues in vitro are mainly responsible for this situation. Until recently, the genetic transformation of monocotyledons was essentially performed by direct transfer of DNA into regenerable protoplasts or intact cells cultured in vitro, via polyethylene glycol treatment, electroporation or particle bombardment. Since 1990, the use of particle gun technology has revolutionized the genetic engineering of monocotyledonous species, allowing transformation to be more independent of the in vitro culture requirements. Today, at least one genotype of each major monocotyledonous crop species, including cereals, can be genetically transformed.

[Tobacco: knowledge, reasoning and opinion of high school students in Doubs. Reflections on prevention]

The prevalence of smoking has increased among young people aged 14 to 18 between 1993 and 1999, and most notably among girls within the same period. These observations illustrate the necessity for significant changes in mass media campaigns and education programmes related to the prevention of smoking among youth. The objective of this survey, initiated by the city of Besançon and the French National Mutual Insurance of Doubs, was to describe and analyse the knowledge and rationale of high school students on tobacco and their opinions in terms of prevention. Twelve public and private high schools in Besançon and Morteau (Doubs-France) participated in the survey; the group also represented a mix of general and professional schools. The questionnaire was filled out by 970 students selected at random. 96% of the students indicated cancer as being the main illness linked to tobacco and 94% stated that second-hand smoke constitutes a health risk. 61% admitted to seeking out the psychoactive effects of smoking. The students responses confirm that the types of messages relayed in a smoking prevention campaign which have an impact on them are: evoking fear of death (74%) and the use of humor (16%). One-third of high school students find that it is unacceptable to forbid smoking on school premises. The knowledge of the dangers related to smoking is not sufficient to keep young people from smoking and confirms that an educational approach based solely on knowledge and facts will not be sufficient to decrease their tobacco consumption. It is important to take into account the image that young people have of tobacco as a means to combat stress in future prevention strategies and campaigns.

Prevalence of HFE mutations in people from North Africa living in southern France

The two main mutations of the HFE (haemochromatosis) gene, C282Y and H63D, were found previously to be rare or absent among Africans. Dried blood samples of 1276 newborns from southern France were analysed for both HFE mutations, and the origins of the four grandparents of each newborn were recorded. The allele frequency of C282Y and H63D was 3.0% +/- 0.7% and 16.9% +/- 1.5% respectively. In a subgroup of 171 newborns with four North African ancestries (mainly from Morocco and Algeria) the allele frequency was 0.9%+2.5%-0.2% for the C282Y and 13.2% +/- 3.6% for H63D. HFE mutations are not absent in individuals with North African origins living in southern Europe. This finding has implications for the diagnosis and screening of hereditary haemochromatosis in these populations.

Accumulation of H/ACA snoRNPs depends on the integrity of the conserved central domain of the RNA-binding protein Nhp2p

Box H/ACA small nucleolar ribonucleoprotein particles (H/ACA snoRNPs) play key roles in the synthesis of eukaryotic ribosomes. How box H/ACA snoRNPs are assembled remains unknown. Here we show that yeast Nhp2p, a core component of these particles, directly binds RNA. In vitro, Nhp2p interacts with high affinity with RNAs containing irregular stem-loop structures but shows weak affinity for poly(A), poly(C) or for double-stranded RNAs. The central region of Nhp2p is believed to function as an RNA-binding domain, since it is related to motifs found in various RNA-binding proteins. Removal of two amino acids that shortens a putative beta-strand element within Nhp2p central domain impairs the ability of the protein to interact with H/ACA snoRNAs in cell extracts. In vivo, this deletion prevents cell viability and leads to a strong defect in the accumulation of H/ACA snoRNAs and Gar1p. These data suggest that proper direct binding of Nhp2p to H/ACA snoRNAs is required for the assembly of H/ACA snoRNPs and hence for the stability of some of their components. In addition, we show that converting a highly conserved glycine residue (G(59)) within Nhp2p central domain to glutamate significantly reduces cell growth at 30 and 37 degrees C. Remarkably, this modification affects the steady-state levels of H/ACA snoRNAs and the strength of Nhp2p association with these RNAs to varying degrees, depending on the nature of the H/ACA snoRNA. Finally, we show that the modified Nhp2p protein whose interaction with H/ACA snoRNAs is impaired cannot accumulate in the nucleolus, suggesting that only the assembled H/ACA snoRNP particles can be efficiently retained in the nucleolus.

The protein kinases AtMAP3Kepsilon1 and BnMAP3Kepsilon1 are functional homologues of S. pombe cdc7p and may be involved in cell division

We identified an Arabidopsis thaliana gene, AtMAP3Kepsilon1, and a Brassica napus cDNA, BnMAP3Kepsilon1, encoding functional protein serine/threonine kinases closely related to cdc7p and Cdc15p from Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively. This is the first report of cdc7-related genes in non-fungal eukaryotes; no such genes have as yet been identified in Metazoans. The B. napus protein is able to partially complement a cdc7 loss of function mutation in S. pombe. RT-PCR and in situ hybridisation revealed that the A. thaliana and B. napus genes are expressed in both the sporophytic and the gametophytic tissues of the respective plant species and revealed further that expression is highest in dividing cells. Moreover, AtMAP3Kepsilon1 gene expression is cell cycle-regulated, with higher expression in G2-M phases. Our results strongly suggest that the plant cdc7p-related protein kinases are involved in a signal transduction pathway similar to the SIN pathway, which positively regulates cytokinesis in S. pombe.

Stable expression in yeast of the mature form of human telomerase RNA depends on its association with the box H/ACA small nucleolar RNP proteins Cbf5p, Nhp2p and Nop10p

Telomerase is a ribonucleoprotein (RNP) particle required for the replication of telomeres. The RNA component, termed hTR, of human telomerase contains a domain structurally and functionally related to box H/ACA small nucleolar RNAs (snoRNAs). Furthermore, hTR is known to be associated with two core components of H/ACA snoRNPs, hGar1p and Dyskerin (the human counterpart of yeast Cbf5p). To assess the functional importance of the association of hTR with H/ACA snoRNP core proteins, we have attempted to express hTR in a genetically tractable system, Saccharomyces cerevisiae. Both mature non-polyadenylated and polyadenylated forms of hTR accumulate in yeast. The former is associated with all yeast H/ACA snoRNP core proteins, unlike TLC1 RNA, the endogenous RNA component of yeast telomerase. We show that the presence of the H/ACA snoRNP proteins Cbf5p, Nhp2p and Nop10p, but not Gar1p, is required for the accumulation of mature non-polyadenylated hTR in yeast, while accumulation of TLC1 RNA is not affected by the absence of any of these proteins. Our results demonstrate that yeast telomerase is unrelated to H/ACA snoRNPs. In addition, they show that the accumulation in yeast of the mature RNA component of human telomerase depends on its association with three of the four core H/ACA snoRNP proteins. It is likely that this is the case in human cells as well.

Nuclear control of mitochondrial genome reorganization characterized using cultured cells of ditelosomic and nullisomic-tetrasomic wheat lines

In vitro-mediated reorganization of the mitochondrial genome is governed by information contained in the nuclear genome. Here we show, from the study of tissue cultures initiated from an almost complete collection of ditelosomic and nullisomic-tetrasomic wheat lines, that nuclear control of the mitochondrial genome structure is a highly complex process. Whereas information responsible for the amplification of defined molecular configurations has been found to be located in either a single or a few chromosomal arms, other rearrangements such as changes in the relative amounts of interconverting subgenomic structures are governed by a number of genes scattered over most of the wheat chromosomes.

Rrp8p is a yeast nucleolar protein functionally linked to Gar1p and involved in pre-rRNA cleavage at site A2

Chemical modifications and processing of the 18S, 5.8S, and 25S ribosomal RNAs from the 35S pre-ribosomal RNA depend on an important set of small nucleolar ribonucleoprotein particles (snoRNPs). Genetic depletion of yeast Gar1p, an essential common component of H/ACA snoRNPs, leads to inhibition of uridine isomerizations to pseudo-uridines on the 35S pre-rRNA and of the early pre-rRNA cleavages at sites A1 and A2, resulting in a loss of mature 18S rRNA synthesis. To identify Gar1p functional partners, we screened for mutations that are synthetically lethal with a gar1 mutant allele encoding a Gar1p mutant protein lacking its two glycine/arginine-rich (GAR) domains. We identified a previously uncharacterized Saccharomyces cerevisiae open reading frame, YDR083W (now designated RRP8), that encodes a highly conserved protein containing motifs found in methyltransferases. Rrp8p localizes to the nucleolus. A yeast strain lacking this protein is viable at 30 degrees C but displays strong growth impairment at lower temperatures. In this strain, cleavage of the pre-rRNA at site A2 is strongly affected whereas cleavages at sites A0 and A1 are only slightly inhibited or delayed.

Peroxynitrite-mediated nitration of the stable free radical tyrosine residue of the ribonucleotide reductase small subunit

Ribonucleotide reductase activity is rate-limiting for DNA synthesis, and inhibition of this enzyme supports cytostatic antitumor effects of inducible NO synthase. The small R2 subunit of class I ribonucleotide reductases contains a stable free radical tyrosine residue required for activity. This radical is destroyed by peroxynitrite, which also inactivates the protein and induces nitration of tyrosine residues. In this report, nitrated residues in the E. coli R2 protein were identified by UV-visible spectroscopy, mass spectrometry (ESI-MS), and tryptic peptide sequencing. Mass analysis allowed the detection of protein R2 as a native dimer with two iron clusters per subunit. The measured mass was 87 032 Da, compared to a calculated value of 87 028 Da. Peroxynitrite treatment preserved the non-heme iron center and the dimeric form of the protein. A mean of two nitrotyrosines per E. coli protein R2 dimer were obtained at 400 microM peroxynitrite. Only 3 out of the 16 tyrosines were nitrated, including the free radical Tyr122. Despite its radical state, that should favor nitration, the buried Tyr122 was not nitrated with a high yield, probably owing to its restricted accessibility. Dose-response curves for Tyr122 nitration and loss of the free radical were superimposed. However, protein R2 inactivation was higher than nitration of Tyr122, suggesting that nitration of the nonconserved Tyr62 and Tyr289 might be also of importance for peroxynitrite-mediated inhibition of E. coli protein R2.

Spin accumulation and domain wall magnetoresistance in 35 nm Co wires

An enhancement of the resistance due to the presence of only one or two isolated domain walls is clearly evidenced by transport measurements in 35 nm epitaxial Co wires, 20 &mgr;m long. The deduced relative change in the resistivity is at least 1 order of magnitude larger than the one predicted from a model based on the mixing of spin channels occurring over the length scale of the domain wall width [P. M. Levy and S. Zhang, Phys. Rev. Lett. 79, 5110 (1997)]. This inconsistency can be resolved by taking the effect of spin accumulation into account, which scales in the case of Co over the much larger distance of the spin diffusion length.

Interactions of nitric oxide with hemoproteins: roles of nitric oxide in mitochondria

Nitric oxide (NO) binds to metalloproteins, and particularly to hemoproteins in both ferrous and ferric states, with association and dissociation rate constants which cover many orders of magnitude. These chemical properties often provide clear explanations of enzymatic specificity. A basic and straightforward description of the versatility of NO chemistry and of the biological relevance of NO effects, as understood by biochemists as opposed to physiologists, is presented. NO effects on hemoglobin and soluble guanylate cyclase, two proteins directly involved in arterio-venous oxygen transport at quite different biological levels, are compared. NO and other N-oxides also play primary roles in several mitochondrial functions. Specific interactions with cytochrome c oxidase and cytochrome c are reviewed, and the effects of NO and other N-oxides on other iron-cluster-containing components of mitochondrial respiration are discussed.

Plant MAP kinase kinase kinases structure, classification and evolution

The increasing number of reports describing plant MAP kinase signalling components reflects the cardinal role that MAP kinase pathways are likely to play during plant growth and development. Relationship and structural analyses of plant MAP kinase kinase kinase related cDNAs and genes established, on one hand, the PMEKKs, which may be distinguished into the alpha, beta, gamma, and zeta groups, and, on the other hand, the PRAFs that consist of the delta, eta and theta groups. Plant MAP3Ks are characterized by different primary structures, but conserved within a single group. A relationship analysis, which included animal, fungal and plant MAP3Ks, revealed a high degree of diversity among this biochemically established set of proteins, thus suggesting a range of biological functions. Four major families emerged, namely the MEKK/STE11, including the PMEKKs, the RAF, including the PRAFs, as well as the MLK and CDC7 families. These four families showed phylum-dependent distributions. Signature sequences characterizing the RAF family and the RAF subfamilies have been evidenced. However, no equivalent sequence motifs were identified for the MEKK/STE11 family, which is highly heterogeneous.

Characterisation of novel plant genes encoding MEKK/STE11 and RAF-related protein kinases

Various elements of the MAP kinase module have been isolated in plants. We describe here the characterisation of 14 new plant cDNAs and genes encoding putative MAP kinase kinase kinases (MAP3Ks) related to the MEKK/STE11 and RAF protein kinases. Plant MAP3Ks are characterised by a variety of primary structures conserved within closely related proteins. Southern blot analysis suggests that plant MAP3Ks are heterogenous in their genomic structure, existing either as single copy genes or as small gene families. An RT-PCR analysis showed that in Arabidopsis thaliana, all organs studied contain detectable levels of transcripts of each of the MAP3K genes identified; however, signals obtained with mature pollen were weak or non-existent except for AtMAP3Kgamma. None of the reported genes share a cell-cycle or a cold stress regulated expression.

Seven novel methylation guide small nucleolar RNAs are processed from a common polycistronic transcript by Rat1p and RNase III in yeast

Through a computer search of the genome of the yeast Saccharomyces cerevisiae, the coding sequences of seven different box C/D antisense small nucleolar RNAs (snoRNAs) with the structural hallmarks of guides for rRNA ribose methylation have been detected clustered over a 1.4-kb tract in an inter-open reading frame region of chromosome XIII. The corresponding snoRNAs have been positively identified in yeast cells. Disruption of the nonessential snoRNA gene cluster specifically suppressed the seven cognate rRNA ribose methylations but did not result in any growth delay under the conditions of yeast culture tested. The seven snoRNAs are processed from a common polycistronic transcript synthesized from an independent promoter, similar to some plant snoRNAs but in marked contrast with their vertebrate functional homologues processed from pre-mRNA introns containing a single snoRNA. Processing of the polycistronic precursor requires nucleases also involved in rRNA processing, i.e., Rnt1p and Rat1p. After disruption of the RNT1 gene, the yeast ortholog of bacterial RNase III, production of the seven mature snoRNAs was abolished, while the polycistronic snoRNA precursor accumulated. In cells lacking functional Rat1p, an exonuclease involved in the processing of both pre-rRNA and intron-encoded snoRNAs, several processing intermediates of the polycistronic precursor accumulated. This allowed for the mapping in the precursor of the presumptive Rnt1p endonucleolytic cuts which provide entry sites for subsequent exonucleolytic trimming of the pre-snoRNAs. In line with known properties of double-stranded RNA-specific RNase III, pairs of Rnt1p cuts map next to each other on opposite strands of long double-helical stems in the secondary structure predicted for the polycistronic snoRNA precursor.

Molecular characterisation of plant cDNAs BnMAP4Kalpha1 and BnMAP4Kalpha2 belonging to the GCK/SPS1 subfamily of MAP kinase kinase kinase kinase

Several yeast and mammal MAP kinase modules require, upstream of their MAP kinase kinase kinase (MAP3K), a MAP3K kinase (MAP4K). An Arabidopsis thaliana EST clone, sharing identity to MAP4Ks from yeast and mammals, has been used to isolate cDNA clones from a Brassica napus microspore-derived embryo cDNA library. The BnMAP4Kalpha1 and BnMAP4K-alpha2 clones encode putative proteins possessing the 12 subdomains of the serine/threonine protein kinase catalytic domain. A detailed analysis showed that they belong to the GCK/SPS1 subfamily of MAP4K proteins which possess an amino terminal catalytic domain and a long carboxy terminal tail. A Southern blot analysis suggested that the two proteins are encoded by a small multigene family. Expression studies revealed the presence of BnMAP4Kalpha1 and -alpha2 transcripts in all the tissues examined; however, they are most abundant in roots, siliques and flower buds. The expression of BnMAP4Kalpha1 and -alpha2 at the three main developmental stages of microspore-derived embryos (i.e., globular/heart, torpedo and cotyledonary) was confirmed by northern blot and RT-PCR analysis. An expression analysis of the above genes using synchronised Arabidopsis thaliana cell suspensions showed that the homologues genes are cell cycle regulated.

Influence of the antioxidant quercetin in vivo on the level of nitric oxide determined by electron paramagnetic resonance in rat brain during global ischemia and reperfusion

We characterized the changes in nitric oxide (NO) levels in the brain during global forebrain ischemia and reperfusion and tested the ability of the natural flavonoid, quercetin, and a synthetic flavonoid, FB277, to increase the amount of available NO by elimination of the superoxide radicals produced during reperfusion. In Sprague-Dawley rats, we used a four-vessel occlusion model of forebrain ischemia (15 min) and reperfusion (30 min). Brain NO was measured on samples of cerebral cortex and cerebellum ex vivo by electron paramagnetic resonance (EPR) spectroscopy. The spin trap used was diethyldithiocarbamate sodium salt (DETC) associated with ferrous citrate. The complex Fe(DETC)2NO was detected at 77 K as a triplet signal at g = 2.035. Groups of animals were treated with quercetin or FB277 (3-morpholinomethyl-3',4',5,7tetramethoxyflavone) or polyethylene glycol-conjugated superoxide dismutase (PEG-SOD). In control (intact anesthetized animals), the signal was about 3 times greater in the cortex than in the cerebellum. During ischemia, the signal rose to 110% in cortex (NS) and 283% in cerebellum (P < 0.05). In reperfusion, it fell again to 91% of control in cerebellum (NS) and 35% in cortex (P < 0.05). Treatment by quercetin (5 mg/kg i.v.) of intact and ischemia-reperfusion groups did not significantly change the signal amplitude in the cerebellum, but did double it in the cortex (to 76% of control) for the ischemia-reperfusion group (P < 0.05). In contrast, FB277 (3.75 mg/kg i.v.) did not increase the signal in the cortex during ischemia-reperfusion, but did do so in the cerebellum (to 152% of control, P < 0.05). The results obtained for PEG-SOD (10,000 U/kg i.v.) were similar to those for FB277. In separate in vitro measurements, we found that quercetin but not FB277 efficiently scavenged superoxide. We hypothesize that quercetin but not FB277 scavenged superoxide anions released in the cortex during reperfusion, thus diminishing the amount of NO removed by the formation of peroxynitrite. The lack of effect of PEG-SOD may be related to the need for chronic treatment to obtain protection.

Microsomal cytochrome P450 dependent oxidation of N-hydroxyguanidines, amidoximes, and ketoximes: mechanism of the oxidative cleavage of their C=N(OH) bond with formation of nitrogen oxides

Oxidation by rat liver microsomes of 13 compounds involving a C=N(OH) function (including N-hydroxyguanidines, amidoximes, ketoximes, and aldoximes) was found to occur with the release of nitrogen oxides such as NO, NO2-, and NO3-. The greatest activities were observed with liver microsomes from dexamethasone-treated rats (up to 8 nmol of NO2- nmol of P450(-)1 min-1). A detailed study of the microsomal oxidation of some of these compounds was performed. Oxidation of N-(4-chlorophenyl)-N'-hydroxy-guanidine led to the formation of the corresponding urea and cyanamide in addition to NO, NO2-, and NO3-. Formation of all these products was dependent on NADPH, O2, and cytochromes P450. Oxidation of two arylamidoximes was found to occur with formation of the corresponding amides and nitriles in addition to nitrogen oxides. Oxidation of 4-(chlorophenyl)methyl ketone oxime gave the corresponding ketone and nitroalkane as well as NO, NO2-, and NO3-. These reactions were also dependent on cytochromes P450 and required NADPH and O2. Mechanistic experiments showed that microsomal oxidations of amidoximes to the corresponding nitriles and of ketoximes to the corresponding nitroalkanes are not inhibited by superoxide dismutase (SOD) and are performed by a cytochrome P450 active species, presumably the high-valent P450-iron-oxo complex. On the contrary, microsomal oxidation of N-hydroxyguanidines to the corresponding cyanamides was greatly inhibited by SOD and appeared to be mainly due to O2*- derived from the oxidase function of cytochromes P450. Similarly, microsomal oxidations of N-hydroxyguanidines and amidoximes to the corresponding ureas and amides were also found to be mainly performed by O2*-, as shown by the great inhibitory effect of SOD (70-100%) and the ability of the xanthine-xanthine oxidase system to give similar oxidation products. However, it is noteworthy that other species, such as the P450 Fe(II)-O2 complex, are also involved, to a minor extent, in the SOD-insensitive microsomal oxidative cleavages of compounds containing a C=N(OH) bond. Our results suggest a general mechanism for such oxidative cleavages of C=N(OH) bonds with formation of nitrogen oxides by cytochromes P450 and NO-synthases, with the involvement of O2*- and its Fe(III) complex [(FeIII-O2-) or (FeII-O2)] as main active species.

Nhp2p and Nop10p are essential for the function of H/ACA snoRNPs

The small nucleolar ribonucleoprotein particles containing H/ACA-type snoRNAs (H/ACA snoRNPs) are crucial trans-acting factors intervening in eukaryotic ribosome biogenesis. Most of these particles generate the site-specific pseudouridylation of rRNAs while a subset are required for 18S rRNA synthesis. To understand in detail how these particles carry out these functions, all of their protein components have to be characterized. For that purpose, we have affinity-purified complexes containing epitope-tagged Gar1p protein, previously shown to be part of H/ACA snoRNPs. Under the conditions used, three polypeptides of 65, 22 and 10 kDa apparent molecular weight specifically copurify with epitope-tagged Gar1p. The 22 and 10 kDa polypeptides were identified as Nhp2p and a novel protein we termed Nop10p, respectively. Both proteins are conserved, essential and present in the dense fibrillar component of the nucleolus. Nhp2p and Nop10p are specifically associated with all H/ACA snoRNAs and are essential to the function of H/ACA snoRNPs. Cells lacking Nhp2p or Nop10p are impaired in global rRNA pseudouridylation and in the A1 and A2 cleavage steps of the pre-rRNA required for the synthesis of mature 18S rRNA. These phenotypes are probably a direct consequence of the instability of H/ACA snoRNAs and Gar1p observed in cells deprived of Nhp2p or Nop10p. Our results suggest that Nhp2p and Nop10p, together with Cbf5p, constitute the core of H/ACA snoRNPs.

Differential sensitivity of the tyrosyl radical of mouse ribonucleotide reductase to nitric oxide and peroxynitrite

Ribonucleotide reductase is essential for DNA synthesis in cycling cells. It has been previously shown that the catalytically competent tyrosyl free radical of its small R2 subunit (R2-Y.) is scavenged in tumor cells co-cultured with macrophages expressing a nitric oxide synthase II activity. We now demonstrate a loss of R2-Y. induced either by .NO or peroxynitrite in vitro. The .NO effect is reversible and followed by an increase in ferric iron release from mouse protein R2. A similar increased iron lability in radical-free, diferric metR2 protein suggests reciprocal stabilizing interactions between R2-Y. and the diiron center in the mouse protein. Scavenging of R2-Y. by peroxynitrite is irreversible and paralleled to an irreversible loss of R2 activity. Formation of nitrotyrosine and dihydroxyphenylalanine was also detected in peroxynitrite-modified protein R2. In R2-overexpressing tumor cells co-cultured with activated murine macrophages, scavenging of R2-Y. following NO synthase II induction was fully reversible, even when endogenous production of peroxynitrite was induced by triggering NADPH oxidase activity with a phorbol ester. Our results did not support the involvement of peroxynitrite in R2-Y. scavenging by macrophage .NO synthase II activity. They confirmed the preponderant physiological role of .NO in the process.

Processing of the precursors to small nucleolar RNAs and rRNAs requires common components

The genes encoding the small nucleolar RNA (snoRNA) species snR190 and U14 are located close together in the genome of Saccharomyces cerevisiae. Here we report that these two snoRNAs are synthesized by processing of a larger common transcript. In strains mutant for two 5'-->3' exonucleases, Xrn1p and Rat1p, families of 5'-extended forms of snR190 and U14 accumulate; these have 5' extensions of up to 42 and 55 nucleotides, respectively. We conclude that the 5' ends of both snR190 and U14 are generated by exonuclease digestion from upstream processing sites. In contrast to snR190 and U14, the snoRNAs U18 and U24 are excised from the introns of pre-mRNAs which encode proteins in their exonic sequences. Analysis of RNA extracted from a dbr1-delta strain, which lacks intron lariat-debranching activity, shows that U24 can be synthesized only from the debranched lariat. In contrast, a substantial level of U18 can be synthesized in the absence of debranching activity. The 5' ends of these snoRNAs are also generated by Xrn1p and Rat1p. The same exonucleases are responsible for the degradation of several excised fragments of the pre-rRNA spacer regions, in addition to generating the 5' end of the 5.8S rRNA. Processing of the pre-rRNA and both intronic and polycistronic snoRNAs therefore involves common components.

The box H + ACA snoRNAs carry Cbf5p, the putative rRNA pseudouridine synthase

Many or all of the sites of pseudouridine (Psi) formation in eukaryotic rRNA are selected by site-specific base-pairing with members of the box H + ACA class of small nucleolar RNAs (snoRNAs). Database searches previously identified strong homology between the rat nucleolar protein Nap57p, its yeast homolog Cbf5p, and the Escherichia coli Psi synthase truB/P35. We therefore tested whether Cbf5p is required for synthesis of Psi in the yeast rRNA. After genetic depletion of Cbf5p, formation of Psi in the pre-rRNA is dramatically inhibited, resulting in accumulation of the unmodified rRNA. Protein A-tagged Cbf5p coprecipitates all tested members of the box H + ACA snoRNAs but not box C + D snoRNAs or other RNA species. Genetic depletion of Cbf5p leads to depletion of all box H + ACA snoRNAs. These include snR30, which is required for pre-rRNA processing. Depletion of Cbf5p also results in a pre-rRNA processing defect similar to that seen on depletion of snR30. We conclude that Cbf5p is likely to be the rRNA Psi synthase and is an integral component of the box H + ACA class of snoRNPs, which function to target the enzyme to its site of action.

Sequence and structural elements of methylation guide snoRNAs essential for site-specific ribose methylation of pre-rRNA

Site-specific 2'-O-ribose methylation of eukaryotic rRNAs is guided by small nucleolar RNAs (snoRNAs). The methylation guide snoRNAs carry long perfect complementaries to rRNAs. These antisense elements are located either in the 5' half or in the 3' end region of the snoRNA, and are followed by the conserved D' or D box motifs, respectively. An uninterrupted helix formed between the rRNA and the antisense element of the snoRNA, in conjunction with the adjacent D' or D box, constitute the recognition signal for the putative methyltransferase. Here, we have identified an additional essential box element common to methylation guide snoRNAs, termed the C' box. We show that the C' box functions in concert with the D' box and plays a crucial role in the methyltransfer reaction directed by the upstream antisense element and the D' box. We also show that an internal fragment of U24 methylation guide snoRNA, encompassing the upstream antisense element and the D' and C' box motifs, can support the site-specific methylation of rRNA. This strongly suggests that the C box of methylation guide snoRNAs plays an essential role in the methyltransfer reaction guided by the 3'-terminal antisense element and the D box of the snoRNA.

A small nucleolar RNP protein is required for pseudouridylation of eukaryotic ribosomal RNAs

Eukaryotic rRNAs possess numerous post-transcriptionally modified nucleotides. The most abundant modifications, 2'-O-ribose methylation and pseudouridylation, occur in the nucleolus during rRNA processing. The nucleolus contains a large number of small nucleolar RNAs (snoRNAs) most of which can be classified into two distinct families defined by conserved sequence boxes and common associated proteins. The C and D box-containing snoRNAs are associated with fibrillarin, and most of them function as guide RNAs in site-specific ribose methylation of rRNAs. The nucleolar function of the other class of snoRNAs, which share box H and ACA elements and are associated with a glycine- and arginine-rich nucleolar protein, Gar1p, remains elusive. Here we demonstrate that the yeast Saccharomyces cerevisiae Gar1 snoRNP protein plays an essential and specific role in the overall pseudouridylation of yeast rRNAs. These results establish a novel function for Gar1 protein and indicate that the box H/ACA snoRNAs, or at least a subset of these snoRNAs, function in the site-specific pseudouridylation of rRNAs.

Purification and characterization of an extracellular heme-binding protein, HasA, involved in heme iron acquisition

Many bacterial hemoproteins involved in heme acquisition have been isolated recently, comprising outer membrane receptors and extracellular heme-binding protein. The mechanisms by which these proteins extract heme have not been described up to now. One such protein, HasA, which can bind free heme as well as capture it from hemoglobin, is secreted by the Gram-negative bacteria Serratia marcescens under iron deficiency conditions. The fact that HasA does not present sequence similarities with other known hemoproteins suggests that it possesses a new type of heme binding site. This work describes the main physicochemical properties of HasA, essential for understanding its function. HasA is a monomer of 19 kDa that binds one b heme per molecule with high affinity. The electron paramagnetic resonance spectra indicate that the heme iron is in a low-spin ferric state and that the two iron axial ligands are His and His-. The low oxidation-reduction potential value (-550 mV vs standard hydrogen electrode) of the heme bound to HasA suggests that heme could be exposed to the solvent. According to circular dichroism data, the binding of heme does not seem to modify the conformation of HasA.

Immunological detection of potential signal-transduction proteins expressed during wheat somatic tissue culture

An immunochemical approach was used to detect the expression of putative guanine nucleotide-binding proteins (G-proteins), arrestin, and nucleoside diphosphate kinases during wheat (Triticum aestivum) tissue culture initiated from immature embryos. Both the soluble and membrane extracts from the immature embryos revealed bands of 58, 40, and 16 kD with antibodies to G-protein (alpha subunit), arrestin, and nucleoside diphosphate kinase, respectively. These proteins were overexpressed in vitro in both nonembryogenic callus and embryogenic cultures. An additional soluble protein (32 kD) was detected by anti-G alpha antibodies in cultured tissues but not in immature embryos, suggesting a possible function in cell multiplication. Moreover, somatic embryogenesis was associated with the appearance of a 29-kD protein reactive with anti-arrstin antibodies, both in soluble and membrane fractions. Tissue-cultured genetic stocks of Chinese Spring wheat, including the disomic, 36 ditelosomic, and 6 nullisomic-tetrasomic wheat lines, were used to ascertain the chromosomal location of the genes encoding the 29-kD arrestin-like protein. The lack of a signal with the nonembryogenic ditelosomic 3 D short chromosome arm line suggests that the 3 D long chromosome arm possesses at least one gene involved in the expression of the 29-kD protein. The putative role of the 29-kD protein in signal-transduction regulating embryogenesis is discussed.

Recombinant [Phe(beta)63]hemoglobin shows rapid oxidation of the beta chains and low-affinity, non-cooperative oxygen binding to the alpha subunits

We have engineered alpha2beta2 [Phe63]hemoglobin by changing the highly conserved distal histidine of the beta chains to a phenylalanine. The mutant tetramer binds four high-affinity ligands, such as CO or NO, to the ferrous form, or CN to the oxidized iron; however, it binds only two low-affinity ligands, oxygen and azide. The absorption spectrum of the ferrous deoxy or ferric forms are not normal, displaying an enhanced absorption of the visible band near 560 nm. Half of the autooxidation process, attributed to the mutated beta subunits, is over 1000-fold faster than for Hb A. The mutant Hb exhibits non-cooperative binding of two oxygens with an affinity about fivefold lower than those of HbA valency hybrids (alpha met beta)2. Functional properties of this mutant Hb resemble those of Hb Saskatoon ([Tyr63]Hb) [Suzuki, T., Hayashi, A., Shimizu, A. & Yamamura, Y. (1966) Biochim. Biophys. Acta 127, 280-282]. Flash-photolysis experiments also indicate non-cooperative behaviour: the CO-recombination kinetics were independent of the fraction dissociated. Furthermore, the amplitude of the CO bimolecular phase was the same for the (alpha(CO)metbeta)2 valency hybrid or the (alphaCO betaCO)2 form, suggesting mainly geminate CO-recombination kinetics to the beta chains. EPR and Resonance Raman spectra did not show evidence for a hemichrome, normally considered as a six-coordinated iron with low-spin character. The EPR and resonance Raman spectra for the mutated beta subunits demonstrate the presence of a high-spin compound in the ferric and deoxy ferrous forms. In particular, the ferrous mutated beta subunits are penta-coordinated. The abnormal absorption spectra are possibly due to an interaction between the porphyrin and the phenyl ring in the distal position rather than to direct binding to the iron.

Growth performance and brain neurotransmitters in pigs as affected by tryptophan, protein, and sex

The effects of dietary levels of tryptophan (TRP) and protein on voluntary feed intake, growth performance, muscle pH, and brain indoleamine and catecholamine concentrations were studied in an experiment involving 48 crossbred Piétrain x Large White pigs (38 kg initial weight). Equal numbers of females, intact males, and barrows were used and they were given ad libitum access to feed during the 28-d experiment. Four dietary treatments were compared in a 2 x 2 factorial arrangement, with the following levels of analyzed TRP and CP: 1) .12 and .16% TRP, suboptimum and optimum for growth, respectively, 2) 12.7% CP of a diet based on corn-soybean meal and adequately balanced for limiting essential amino acids other than TRP; and 16.7% CP diet with additional protein from corn gluten meal. Dietary CP interacted with TRP on feed intake and growth, with a greater depressive effect at .12% TRP than at .16% TRP in the three genders. Norepinephrine concentration, which was the highest in the preoptic area, was higher in females than in intact or castrated males. Serotonin concentration was increased by TRP supplementation in the different brain regions. Additional CP depressed serotonin concentration more at .12% TRP than at .16% TRP. The greater sensitivity of feed intake and growth of pigs, especially females, to TRP deficiency in the presence of additional CP may have been related to a more critical serotonergic activity, when hypothalamic serotonin concentration fell below a threshold level. Supplemental TRP increased muscle pH, both at 45 min and 24 h after death, in ham (adductor femoris and semimembranosus) and loin (longissimus), suggesting a sedative effect of TRP for reducing stress response.

Site-specific ribose methylation of preribosomal RNA: a novel function for small nucleolar RNAs

Eukaryotic cells contain many fibrillarin-associated small nucleolar RNAs (snoRNAs) that possess long complementarities to mature rRNAs. Characterization of 21 novel antisense snoRNAs from human cells followed by genetic depletion and reconstitution studies on yeast U24 snoRNA provides evidence that this class of snoRNAs is required for site-specific 2'-O-methylation of preribosomal RNA (pre-rRNA). Antisense sno-RNAs function through direct base-pairing interactions with pre-rRNA. The antisense element, together with the D or D' box of the snoRNA, provide the information necessary to select the target nucleotide for the methyltransfer reaction. The conclusion that sno-RNAs function in covalent modification of the sugar moieties of ribonucleotides demonstrates that eukaryotic small nuclear RNAs have a more versatile cellular function than earlier anticipated.

Characterization of bacterial cytochrome cd(1)-nitrite reductase as one enzyme responsible for catalysis of nitrosation of secondary amines

Bacterial formation of carcinogenic N-nitroso compounds may play a role in the etiology of human cancer. Biochemical and immunological studies in denitrifying bacteria (Pseudomonas aeruginosa) strongly support the identification of cytochrome cd(1)-nitrite reductase as the enzyme responsible for the catalysis of nitrosation through the production of nitric oxide or NO(+)-like species. Interestingly, electron paramagnetic resonance studies have shown that large quantities of nitric oxide or NO(+)-species were also produced by non-denitrifying enterobacteria (Escherichia coli, Proteus morganii).

Processing of the yeast pre-rRNA at sites A(2) and A(3) is linked

Cleavage of the yeast pre-rRNA at site A(2) in internal transcribed spacer 1 (ITS1) requires multiple snoRNP species, whereas cleavage at site A(3),located 72 nt 3' in ITS1, requires Rnase MRP. Analyses of mutations in the pre- rRNA have revealed an unexpected link between processing at A(2) and A(3). Small substitution mutations in the 3' flanking sequence at A(2) inhibit processing at site A(3), whereas a small deletion at A(3) has been shown to delay processing at site A(2). Moreover, the combination of mutations in cis at both A(2) and A(3) leads to the synthesis of pre-rRNA species with 5' ends within the mature 18S rRNA sequence, at sites between + 482 and + 496. The simultaneous interference with an snoRNP processing complex at site A(2) and an Rnase MPRP complex at site A(3) may activate a pre-rRNA breakdown pathway. The same aberantpre-rRNA species are observed in strains with mutations in the RNA component of Rnase MRP, consistent with interactions between the processing complexes. Furthermore, genetic depletion of the snoRNA, snR30, has been shown to affect the coupling between cleavage by Rnase MRP and subsequent exonuclease digestion.We conclude that an sno-RNP-dependent processing complex that is required for A(2) cleavage and that recognizes the 3' flanking sequence at A(2), interacts with the RNase MRP complex bound to the pre-rRNA around site A(3).