The epigenetic footprint of poleward range-expanding plants in apomictic dandelions.

Epigenetic modifications, such as DNA methylation variation, can generate heritable phenotypic variation independent of the underlying genetic code. However, epigenetic variation in natural plant populations is poorly documented and little understood. Here, we test whether northward range expansion of obligate apomicts of the common dandelion (Taraxacum officinale) is associated with DNA methylation variation. We characterized and compared patterns of genetic and DNA methylation variation in greenhouse-reared offspring of T. officinale that were collected along a latitudinal transect of northward range expansion in Europe. Genetic AFLP and epigenetic MS-AFLP markers revealed high levels of local diversity and modest but significant heritable differentiation between sampling locations and between the southern, central and northern regions of the transect. Patterns of genetic and epigenetic variation were significantly correlated, reflecting the genetic control over epigenetic variation and/or the accumulation of lineage-specific spontaneous epimutations, which may be selectively neutral. In addition, we identified a small component of DNA methylation differentiation along the transect that is independent of genetic variation. This epigenetic differentiation might reflect environment-specific induction or, in case the DNA methylation variation affects relevant traits and fitness, selection of heritable DNA methylation variants. Such generated epigenetic variants might contribute to the adaptive capacity of individual asexual lineages under changing environments. Our results highlight the potential of heritable DNA methylation variation to contribute to population differentiation along ecological gradients. Further studies are needed using higher resolution methods to understand the functional significance of such natural occurring epigenetic differentiation.

Silene as a model system in ecology and evolution.

The genus Silene, studied by Darwin, Mendel and other early scientists, is re-emerging as a system for studying interrelated questions in ecology, evolution and developmental biology. These questions include sex chromosome evolution, epigenetic control of sex expression, genomic conflict and speciation. Its well-studied interactions with the pathogen Microbotryum has made Silene a model for the evolution and dynamics of disease in natural systems, and its interactions with herbivores have increased our understanding of multi-trophic ecological processes and the evolution of invasiveness. Molecular tools are now providing new approaches to many of these classical yet unresolved problems, and new progress is being made through combining phylogenetic, genomic and molecular evolutionary studies with ecological and phenotypic data.

Chemical defense, mycorrhizal colonization and growth responses in Plantago lanceolata L.

Allelochemicals defend plants against herbivore and pathogen attack aboveground and belowground. Whether such plant defenses incur ecological costs by reducing benefits from plant mutualistic symbionts is largely unknown. We explored a potential trade-off between inherent plant chemical defense and belowground mutualism with arbuscular mycorrhizal fungi (AMF) in Plantago lanceolata L., using plant genotypes from lines selected for low and high constitutive levels of the iridoid glycosides (IG) aucubin and catalpol. As selection was based on IG concentrations in leaves, we first examined whether IG concentrations covaried in roots. Root and leaf IG concentrations were strongly positively correlated among genotypes, indicating genetic interdependence of leaf and root defense. We then found that root AMF arbuscule colonization was negatively correlated with root aucubin concentration. This negative correlation was observed both in plants grown with monocultures of Glomus intraradices and in plants colonized from whole-field soil inoculum. Overall, AMF did not affect total biomass of plants; an enhancement of initial shoot biomass was offset by a lower root biomass and reduced regrowth after defoliation. Although the precise effects of AMF on plant biomass varied among genotypes, plants with high IG levels and low AMF arbuscule colonization in roots did not produce less biomass than plants with low IG and high AMF arbuscule colonization. Therefore, although an apparent trade-off was observed between high root chemical defense and AMF arbuscule colonization, this did not negatively affect the growth responses of the plants to AMF. Interestingly, AMF induced an increase in root aucubin concentration in the high root IG genotype of P. lanceolata. We conclude that AMF does not necessarily stimulate plant growth, that direct plant defense by secondary metabolites does not necessarily reduce potential benefits from AMF, and that AMF can enhance concentrations of root chemical defenses, but that these responses are plant genotype-dependent.

Disease status and population origin effects on floral scent:: potential consequences for oviposition and fruit predation in a complex interaction between a plant, fungus, and noctuid moth.

In the Silene latifolia-Hadena bicruris nursery pollination system, the Hadena moth is both pollinator and seed predator of its host plant. Floral scent, which differs among S. latifolia individuals and populations, is important for adult Hadena to locate its host. However, the success of moth larvae is strongly reduced if hosts are infected by the anther smut fungus Microbotryum violaceum, a pathogen that is transmitted by flower visitors. There were no qualitative differences between the scent of flowers from healthy and diseased plants. In addition, electroantennographic measurements showed that Hadena responded to the same subset of 19 compounds in samples collected from healthy and diseased plants. However, there were significant quantitative differences in scent profiles. Flowers from diseased plants emitted both a lower absolute amount of floral scent and had a different scent pattern, mainly due to their lower absolute amount of lilac aldehyde, whereas their amount of (E)-beta-ocimene was similar to that in healthy flowers. Dual choice behavioral wind tunnel tests using differently scented flowers confirmed that moths respond to both qualitative and quantitative aspects of floral scent, suggesting that they could use differences in floral scent between healthy and infected plants to discriminate against diseased plants. Population mean fruit predation rates significantly increased with population mean levels of the emission rates of lilac aldehyde per flower, indicating that selection on floral scent compounds may not only be driven by effects on pollinator attraction but also by effects on fruit predation. However, variation in mean emission rates of scent compounds per flower generally could not explain the higher fruit predation in populations originating from the introduced North American range compared to populations native to Europe.

Oviposition cues for a specialist butterfly--plant chemistry and size.

The oviposition choice of an insect herbivore is based on a complex set of stimuli and responses. In this study, we examined the effect of plant secondary chemistry (the iridoid glycosides aucubin and catalpol) and aspects of size of the plant Plantago lanceolata, on the oviposition behavior of the specialist butterfly Melitaea cinxia. Iridoid glycosides are known to deter feeding or decrease the growth rate of generalist insect herbivores, but can act as oviposition cues and feeding stimulants for specialized herbivores. In a previous observational study of M. cinxia in the field, oviposition was associated with high levels of aucubin. However, this association could have been the cause (butterfly choice) or consequence (plant induction) of oviposition. We conducted a set of dual- and multiple-choice experiments in cages and in the field. In the cages, we found a positive association between the pre-oviposition level of aucubin and the number of ovipositions. The association reflects the butterfly oviposition selection rather than plant induction that follows oviposition. Our results also suggest a threshold concentration below which females do not distinguish between levels of iridoid glycosides. In the field, the size of the plant appeared to be a more important stimulus than iridoid glycoside content, with bigger plants receiving more oviposition than smaller plants, regardless of their secondary chemistry. Our results illustrate that the rank of a cue used for oviposition may be dependent on environmental context.

Habitat-specific natural selection at a flowering-time QTL is a main driver of local adaptation in two wild barley populations.

Understanding the genetic basis of local adaptation requires insight in the fitness effects of individual loci under natural field conditions. While rapid progress is made in the search for genes that control differences between plant populations, it is typically unknown whether the genes under study are in fact key targets of habitat-specific natural selection. Using a quantitative trait loci (QTL) approach, we show that a QTL associated with flowering-time variation between two locally adapted wild barley populations is an important determinant of fitness in one, but not in the other population's native habitat. The QTL mapped to the same position as a habitat-specific QTL for field fitness that affected plant reproductive output in only one of the parental habitats, indicating that the genomic region is under differential selection between the native habitats. Consistent with the QTL results, phenotypic selection of flowering time differed between the two environments, whereas other traits (growth rate and seed weight) were under selection but experienced no habitat-specific differential selection. This implies the flowering-time QTL as a driver of adaptive population divergence. Our results from phenotypic selection and QTL analysis are consistent with local adaptation without genetic trade-offs in performance across environments, i.e. without alleles or traits having opposing fitness effects in contrasting environments.

Aspergilosis necrotizante crónica en un paciente con secuelas de tuberculosis pulmonar / Chronic necrotizing aspergillosis in a patient with pulmonary tuberculosis sequelae

Aspergillus fumigatus is the causative agent of differents pathologies in the human being: aspergilloma, allergic bronchopulmonary aspergillosis, chronic necrotizing aspergillosis and invasive aspergillosis. In chronic necrotizing aspergillosis there is local invasion of the lung tissue and parenchyma destruction. Chronic necrotizing aspergillosis is different from invasive aspergillosis, because the abscence of vascular invasion or dissemination. Chronic necrotizing aspergillosis is seen in middle-aged and elderly with underlying lung diseases: COPD, tuberculosis sequelae, lung resection, pneumoconiosis, radiotherapy, lung infarction or sarcoidosis. Clinical manifestations are non specific, being the most usual fever, cough, sputum production and weight loss. Incidence of chronic necrotizing aspergillosis is unknown in Chile. Chronic necrotizing aspergillosis can produce death. It requires early diagnosis and treatment. In a patient with a predisposing disease and with prolonged fever and consuntive status, diagnosis of chronic necrotizing aspergillosis should be considered. We present a patient with chronic necrotizing aspergillosis attended at Instituto Nacional del Tórax (Thorax National Institute) in Santiago.

Aspergillus fumigatus puede causar diferentes patologías en el ser humano: aspergiloma, aspergilosis broncopulmonar alérgica, aspergilosis necrotizante crónica, aspergilosis invasora. En la aspergilosis necrotizante crónica hay invasión local del parénquima y destrucción. A diferencia de la aspergilosis invasora no invade vasos sanguíneos ni se disemina a otros órganos. La aspergilosis necrotizante crónica se presenta en pacientes de edad media o ancianos con patología pulmonar previa: EPOC, secuelas de tuberculosis, resección pulmonar, neumoconiosis, radioterapia, infarto pulmonar o sarcoidosis. La clínica es indolente e inespecífica, con fiebre, tos, expectoración y baja de peso. Se desconoce la incidencia de aspergilosis necrotizante crónica en nuestro medio. La aspergilosis necrotizante crónica es potencialmente fatal, por lo que requiere de un diagnóstico y tratamiento oportuno. Creemos que, debe considerarse esta entidad ante un cuadro consuntivo y febril prolongado, en pacientes con enfermedades predisponentes que producen una leve baja de la inmunidad. Describimos el caso de un paciente atendido en el Instituto Nacional del Tórax.

Optimum and maximum host sizes at parasitism for the endoparasitoid Hyposoter didymator (Hymenoptera: Ichneumonidae) differ greatly between two host species.

Host size is considered a reliable indicator of host quality and an important determinant of parasitoid fitness. Koinobiont parasitoids attack hosts that continue feeding and growing during parasitism. In contrast with hemolymph-feeding koinobionts, tissue-feeding koinobionts face not only a minimum host size for successful development but also a maximum host size, because consumption of the entire host is often necessary for successful egression. Here we study interactions between a generalist tissue-feeding larval endoparasitoid, Hyposoter didymator Thunberg (Hymenoptera: Ichneumonidae) and two of its natural hosts, Spodoptera exigua Hübner and Chrysodeixis chalcites Esper (Lepidoptera: Noctuidae). Larvae of C. chalcites are up to three times larger than corresponding instars of S. exigua and also attain much higher terminal masses before pupation. We hypothesized that the range of host instars suitable for successful parasitism by H. didymator would be much more restricted in the large host C. chalcites than in the smaller S. exigua. To test this hypothesis, we monitored development of H. didymator in all instars of both host species and measured survival, larval development time, and adult body mass of the parasitioid. In contrast with our predictions, C. chalcites was qualitatively superior to S. exigua in terms of the survival of parasitized hosts, the proportion of parasitoids able to complete development, and adult parasitoid size. However, in both hosts, the proportion of mature parasitoid larvae that successfully developed into adults was low at the largest host sizes. Our results suggest that qualitative, as well as quantitative, factors are important in the success of tissue-feeding parasitoids.

Host-related genetic differentiation in the anther smut fungus Microbotryum violaceum in sympatric, parapatric and allopatric populations of two host species Silene latifolia and S. dioica.

We investigated genetic diversity in West European populations of the fungal pathogen Microbotryum violaceum in sympatric, parapatric and allopatric populations of the host species Silene latifolia and S. dioica, using four polymorphic microsatellite loci. In allopatric host populations, the fungus was highly differentiated by host species, exhibiting high values of F(ST) and R(ST), and revealed clear and distinct host races. In sympatric and parapatric populations we found significant population differentiation as well, except for one sympatric population in which the two host species grew truly intermingled. The mean number of alleles per locus for isolates from each of the host species was significantly higher in sympatric/parapatric than in allopatric populations. This suggests that either gene flow between host races in sympatry, or in case of less neutral loci, selection in a more heterogeneous host environment can increase the level of genetic variation in each of the demes. The observed pattern of host-related genetic differentiation among these geographically spread populations suggest a long-term divergence between these host races. In sympatric host populations, both host races presumably come in secondary contact, and host-specific alleles are exchanged depending on the amount of fungal gene flow.

Differential selection of growth rate-related traits in wild barley, Hordeum spontaneum, in contrasting greenhouse nutrient environments.

Across-species comparisons show that inherent variation in relative growth rate (RGR) and its underlying traits are correlated with habitat productivity. In this study, we test the hypothesis that growth rate-related traits confer differential selective effects in contrasting nutrient environments. We specifically test whether high RGR is targeted by selection in nutrient-rich environments whereas low values of traits that underlie RGR [specific leaf area (SLA), leaf mass fraction and leaf area ratio (LAR)] confer a direct fitness advantage in nutrient-poor environments, resulting in selection of low RGR as a correlated response. We measured RGR, its underlying component traits, and estimated fitness in a range of wild barley (Hordeum spontaneum) accessions grown under high and low nutrient conditions. Selection on component traits differed between the two environments, while total selection of RGR was not significant. Using multiple regression and path analysis to estimate direct fitness effects, a selective advantage of high LAR and SLA was demonstrated only under nutrient-rich conditions. While supporting the view that observed associations between habitat richness and some RGR-component traits reflect adaptation to differing nutrient regimes, our data suggest that direct selection targets component traits rather than RGR itself.

Parkinson's disease-associated alpha-synuclein is more fibrillogenic than beta- and gamma-synuclein and cannot cross-seed its homologs.

Parkinson's disease (PD) is a neurodegenerative disorder that is pathologically characterized by the presence of intracytoplasmic Lewy bodies. Recently, two point mutations in alpha-synuclein were found to be associated with familial PD, but as of yet no mutations have been described in the homologous genes beta- and gamma-synuclein. alpha-Synuclein forms the major fibrillar component of Lewy bodies, but these do not stain for beta- or gamma-synuclein. This result is very surprising, given the extent of sequence conservation and the high similarity in expression and subcellular localization, in particular between alpha- and beta-synuclein. Here we compare in vitro fibrillogenesis of all three purified synucleins. We show that fresh solutions of alpha-, beta-, and gamma- synuclein show the same natively unfolded structure. While over time alpha-synuclein forms the previously described fibrils, no fibrils could be detected for beta- and gamma-synuclein under the same conditions. Most importantly, beta- and gamma-synuclein could not be cross-seeded with alpha-synuclein fibrils. However, under conditions that drastically accelerate aggregation, gamma-synuclein can form fibrils with a lag phase roughly three times longer than alpha-synuclein. These results indicate that beta- and gamma-synuclein are intrinsically less fibrillogenic than alpha-synuclein and cannot form mixed fibrils with alpha-synuclein, which may explain why they do not appear in the pathological hallmarks of PD, although they are closely related to alpha-synuclein and are also abundant in brain.

Beta-secretase cleavage of Alzheimer's amyloid precursor protein by the transmembrane aspartic protease BACE.

Cerebral deposition of amyloid beta peptide (Abeta) is an early and critical feature of Alzheimer's disease. Abeta generation depends on proteolytic cleavage of the amyloid precursor protein (APP) by two unknown proteases: beta-secretase and gamma-secretase. These proteases are prime therapeutic targets. A transmembrane aspartic protease with all the known characteristics of beta-secretase was cloned and characterized. Overexpression of this protease, termed BACE (for beta-site APP-cleaving enzyme) increased the amount of beta-secretase cleavage products, and these were cleaved exactly and only at known beta-secretase positions. Antisense inhibition of endogenous BACE messenger RNA decreased the amount of beta-secretase cleavage products, and purified BACE protein cleaved APP-derived substrates with the same sequence specificity as beta-secretase. Finally, the expression pattern and subcellular localization of BACE were consistent with that expected for beta-secretase. Future development of BACE inhibitors may prove beneficial for the treatment of Alzheimer's disease.

alpha-synuclein fibrillogenesis is nucleation-dependent. Implications for the pathogenesis of Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disorder that is pathologically characterized by the presence of intracytoplasmic Lewy bodies, the major components of which are filaments consisting of alpha-synuclein. Two recently identified point mutations in alpha-synuclein are the only known genetic causes of PD. alpha-Synuclein fibrils similar to the Lewy body filaments can be formed in vitro, and we have shown recently that both PD-linked mutations accelerate their formation. This study addresses the mechanism of alpha-synuclein aggregation: we show that (i) it is a nucleation-dependent process that can be seeded by aggregated alpha-synuclein functioning as nuclei, (ii) this fibril growth follows first-order kinetics with respect to alpha-synuclein concentration, and (iii) mutant alpha-synuclein can seed the aggregation of wild type alpha-synuclein, which leads us to predict that the Lewy bodies of familial PD patients with alpha-synuclein mutations will contain both, the mutant and the wild type protein. Finally (iv), we show that wild type and mutant forms of alpha-synuclein do not differ in their critical concentrations. These results suggest that differences in aggregation kinetics of alpha-synucleins cannot be explained by differences in solubility but are due to different nucleation rates. Consequently, alpha-synuclein nucleation may be the rate-limiting step for the formation of Lewy body alpha-synuclein fibrils in Parkinson's disease.

Both familial Parkinson's disease mutations accelerate alpha-synuclein aggregation.

Parkinson's disease (PD) is a neurodegenerative disorder that is pathologically characterized by the presence of intracytoplasmic Lewy bodies, the major component of which are filaments consisting of alpha-synuclein. Two recently identified point mutations in alpha-synuclein are the only known genetic causes of PD, but their pathogenic mechanism is not understood. Here we show that both wild type and mutant alpha-synuclein form insoluble fibrillar aggregates with antiparallel beta-sheet structure upon incubation at physiological temperature in vitro. Importantly, aggregate formation is accelerated by both PD-linked mutations. Under the experimental conditions, the lag time for the formation of precipitable aggregates is about 280 h for the wild type protein, 180 h for the A30P mutant, and only 100 h for the A53T mutant protein. These data suggest that the formation of alpha-synuclein aggregates could be a critical step in PD pathogenesis, which is accelerated by the PD-linked mutations.

Permeability and residual plasma volume of human, Dutch variant, and rat amyloid beta-protein 1-40 at the blood-brain barrier.

The permeability of normal human, the human Dutch variant, and the rat A beta 1-40 proteins at the blood-brain barrier (BBB) was determined in the normal adult rat by quantifying the permeability coefficient-surface area (PS) product for each protein after correction for the residual plasma volume (Vp) occupied by the protein in the blood vessels of different brain regions. The PS for normal and Dutch A beta ranged from 13 x 10(-6) to 22 x 10(-6) ml/g/s in different brain regions, which is 130 to 220 times greater than albumin. These high PS values compare to that of insulin, whose uptake is decidedly by a receptor-mediated transport process, and suggest a similar mechanism for A beta. Remarkably, the PS for rat A beta was 4 times higher and ranged from 54 x 10(-6) to 82 x 10(-6) ml/g/s for different brain regions, suggesting a distinctive species specificity. While the Vp values of human and rat A beta were comparable, the Dutch variant was 2 to 3 times higher, indicating adherence to the vessel walls in different brain regions, consistent with the heavy A beta deposition that has been described in intracerebral vessel walls with this variant. The high PS values observed for A beta at the BBB suggest that sources outside the nervous system could contribute, at least in part, to the cerebral A beta deposits seen in Alzheimer's disease. SDS-PAGE of 125I-labeled human A beta after 60 min of uptake revealed intact protein in plasma and in different brain regions. In addition, 125I-labeled human A beta binding to a protein of 67,000 in both plasma and brain tissue regions was observed with SDS-PAGE. This protein was tentatively identified as albumin, and it was not detectable in the brain regions of animals that had undergone intracardiac perfusion; hence, a portion of A beta binds tightly to and is likely transported by albumin in plasma. The absence of this A beta-albumin complex in brain regions after perfusion and the low permeability of albumin at the BBB imply that A beta itself is efficiently transported at the BBB to account for the high PS values, although presentation of A beta to the capillary endothelial cell by albumin or other plasma proteins cannot be excluded.

Amyloid beta-peptide is transported on lipoproteins and albumin in human plasma.

The amyloid beta-peptide (Abeta) is the major constituent of neuritic plaques in Alzheimer's disease and occurs as a soluble 40-42-residue peptide in cerebrospinal fluid and blood of both normal and AD subjects. It is unclear whether Abeta, once it is secreted by cells, remains free in biological fluids or is associated with other proteins and thus transported and metabolized with them. Such knowledge of the normal fate of Abeta is a prerequisite for understanding the changes that may lead to the pathological aggregation of soluble Abeta in vivo, the possible influence of certain extracellular proteins, particularly apolipoprotein E, on plaque formation, and the pharmacology of putative Abeta-lowering drugs. To address the question of Abeta distribution in human biological fluids, we incubated fresh human plasma from 38 subjects with physiological concentrations (0.5-0.7 nM) of radioiodinated Abeta1-40 and seven plasma samples with Abeta1-42. Lipoproteins and lipid-free proteins were separated and analyzed for bound iodinated Abeta1-40. We found that up to 5% of Abeta added to plasma is bound to selected lipoproteins: very low density, low density, and high density, but not lipoprotein(a). The large majority ( approximately 89%), however, is bound to albumin, and very little Abeta is free. Abeta distribution in plasma was not significantly influenced by apolipoprotein E genotype. We conclude that Abeta is normally bound to and transported by albumin and specific lipoproteins in human plasma under physiological conditions.

Evidence that the 42- and 40-amino acid forms of amyloid beta protein are generated from the beta-amyloid precursor protein by different protease activities.

Cerebral deposition of the amyloid beta protein (A beta) is an early and invariant feature of Alzheimer disease (AD). Whereas the 40-amino acid form of A beta (A beta 40) accounts for approximately 90% of all A beta normally released from cells, it appears to contribute only to later phases of the pathology. In contrast, the longer more amyloidogenic 42-residue form (A beta 42), accounting for only approximately 10% of secreted A beta, is deposited in the earliest phase of AD and remains the major constituent of most amyloid plaques throughout the disease. Moreover, its levels have been shown to be increased in all known forms of early-onset familial AD. Thus, inhibition of A beta 42 production is a prime therapeutic goal. The same protease, gamma-secretase, is assumed to generate the C termini of both A beta 40 and A beta 42. Herein, we analyze the effect of the compound MDL 28170, previously suggested to inhibit gamma-secretase, on beta-amyloid precursor protein processing. By immunoprecipitating conditioned medium of different cell lines with various A beta 40- and A beta 42-specific antibodies, we demonstrate a much stronger inhibition of the gamma-secretase cleavage at residue 40 than of that at residue 42. These data suggest that different proteases generate the A beta 40 and A beta 42 C termini. Further, they raise the possibility of identifying compounds that do not interfere with general beta-amyloid precursor protein metabolism, including A beta 40 production, but specifically block the generation of the pathogenic A beta 42 peptide.

Co-expression of beta-amyloid precursor protein (betaAPP) and apolipoprotein E in cell culture: analysis of betaAPP processing.

Apolipoprotein E (ApoE) is the major genetic risk factor for Alzheimer's disease (AD). The ApoE4 allele is associated with earlier disease onset and greater cerebral deposition of the amyloid beta peptide (Abeta), the major constituent of senile (amyloid) plaques. The molecular mechanism underlying these effects of ApoE4 remains unclear; ApoE alleles could have different influences on Abeta production, extracellular aggregation, or clearance. Because the missense mutations on chromosomes 14 and 21 that cause familial forms of AD appear to lead to increased secretion of Abeta, it is important to determine whether ApoE4 has a similar effect. Here, we have examined the effects of all three ApoE alleles on the processing of betaAPP and the secretion of Abeta in intact cells. We established neural (HS683 human glioma) and non-neural (Chinese hamster ovary) cell culture systems that constitutively secrete both ApoE and Abeta at concentrations like those in human cerebrospinal fluid. betaAPP metabolites, generated in the presence of each ApoE allele, were analysed and quantified by two methods: immunoprecipitation and phosphorimaging, and ELISA. We detected no consistent allele-specific effects of ApoE on betaAPP processing in either cell type. Our data suggest that the higher amyloid burden found in AD subjects expressing ApoE4 is not due to increased amyloidogenic processing of betaAPP, in contrast to findings in AD linked to chromosome 14 or 21. These co-expressing cell lines will be useful in the further search for the effects of ApoE on Abeta aggregation or clearance under physiologically relevant conditions.

Transcriptional control via translational repression by c4 antisense RNA of bacteriophages P1 and P7.

The c4 repressors of bacteriophages P1 and P7 are antisense RNAs that inhibit antirepressor synthesis. This antisense inhibition is unusual in that the c4 repressor and the repressed genes orfx and ant are cotranscribed in that order from the same promoter, and c4 RNA is processed from a precursor RNA. Here, we show that c4 RNA directly represses translation of orfx, a small open reading frame, to which ant is translationally coupled. This translational repression blocks ant transcription via a rho-dependent terminator. Thus, c4 RNA controls expression of the ant gene by a novel indirect mechanism combining translational repression, translational coupling, and rho-dependent termination.