Further Evidence for the Relationship between Light-Induced Changes of Plasmalemma Transport and Transthylakoid Proton Uptake

The simultaneous measurement of the induction curves of chlorophyllfluorescence, its responses to saturating flashes, light-scatteringat 532 nm, and plasmalemma voltage supports previous findings(Hansen, Kolbowski, and Dau, 1987), that light-induced uptakeof protons into the inner thylakoid space causes the rapid (5to 20 s) light-induced depolarization at the plasmalemma viasubstrate depletion of the electrogenic H⁺-pump. These conclusionsare based on kinetic studies which enable the separation ofindividual components in complex signals by means of their assignmentto different time-constants. In contrast to the previous investigation,binary noise was used for modulation of the actinic light. Thenew input signal not only increased the reliability of the previousresults obtained by sine-waves, but also led to the detectionof three additional time-constants. One of these is probablyrelated to the action of light on the potassium channel of theplasmalemma. The others are assigned to the quencher Q and toa still unknown process. Key words: Chlorophyll fluorescence, plasmalemma potential, proton fluxes, noise, scattering, spinach, state-transitions, thylakoid membrane     

CTCF-dependent chromatin bias constitutes transient epigenetic memory of the mother at the H19-Igf2 imprinting control region in prospermatogonia

Genomic imprints-parental allele-specific DNA methylation marks at the differentially methylated regions (DMRs) of imprinted genes-are erased and reestablished in germ cells according to the individual's sex. Imprint establishment at paternally methylated germ line DMRs occurs in fetal male germ cells. In prospermatogonia, the two unmethylated alleles exhibit different rates of de novo methylation at the H19/Igf2 imprinting control region (ICR) depending on parental origin. We investigated the nature of this epigenetic memory using bisulfite sequencing and allele-specific ChIP-SNuPE assays. We found that the chromatin composition in fetal germ cells was biased at the ICR between the two alleles with the maternally inherited allele exhibiting more H3K4me3 and less H3K9me3 than the paternally inherited allele. We determined genetically that the chromatin bias, and also the delayed methylation establishment in the maternal allele, depended on functional CTCF insulator binding sites in the ICR. Our data suggest that, in primordial germ cells, maternally inherited allele-specific CTCF binding sets up allele-specific chromatin differences at the ICR. The erasure of these allele-specific chromatin marks is not complete before the process of de novo methylation imprint establishment begins. CTCF-dependent allele-specific chromatin composition imposes a maternal allele-specific delay on de novo methylation imprint establishment at the H19/Igf2 ICR in prospermatogonia.     

A Population-Structured HIV Epidemic in Israel: Roles of Risk and Ethnicity

Background

HIV in Israel started with a subtype-B epidemic among men who have sex with men, followed in the 1980s and 1990s by introductions of subtype C from Ethiopia (predominantly acquired by heterosexual transmission) and subtype A from the former Soviet Union (FSU, most often acquired by intravenous drug use). The epidemic matured over the last 15 years without additional large influx of exogenous infections. Between 2005 and 2013 the number of infected men who have sex with men (MSM) increased 2.9-fold, compared to 1.6-fold and 1.3-fold for intravenous drug users (IVDU) and Ethiopian-origin residents. Understanding contemporary spread is essential for effective public health planning.

Methods

We analyzed demographic and virologic data from 1,427 HIV-infected individuals diagnosed with HIV-I during 1998–2012. HIV phylogenies were reconstructed with maximum-likelihood and Bayesian methods.

Results

Subtype-B viruses, but not A or C, demonstrated a striking number of large clusters with common ancestors having posterior probability ≥0.95, including some suggesting presence of transmission networks. Transmitted drug resistance was highest in subtype B (13%). MSM represented a frequent risk factor in cross-ethnic transmission, demonstrated by the presence of Israeli-born with non-B virus infections and FSU immigrants with non-A subtypes.

Conclusions

Reconstructed phylogenetic trees demonstrated substantial grouping in subtype B, but not in non-MSM subtype-A or in subtype-C, reflecting differences in transmission dynamics linked to HIV transmission categories. Cross-ethnic spread occurred through multiple independent introductions, with MSM playing a prevalent role in the transmission of the virus. Such data provide a baseline to track epidemic trends and will be useful in informing and quantifying efforts to reduce HIV transmission.     

Individual differences in response to an open field test by the guppy—Poecilia reticulata (Peters)

Guppies Poecilia reticulata (Peters) were subjected to repeated measures of 5 min duration, on an open field test. The major measures were the number of times a fish changed sections, the number of different sections entered regardless of how many times they entered a section and the ratio of inner to outer sections entered. The activity scores were on a continuous distribution from fish to fish and for the males correlated highly with the ratio of inner to outer movements, but not so for the females. All fish showed a preference for the outer rings compared to the inner rings. There was a non–significant tendency for the male activity to increase during each test, but to wane as the number of tests increased. The females showed a variation of activity which may be associated with their ovarian cycle, but the various activity measures tended not to correlate with each other during the cycle and also failed to correlate with various published cycles of physiological ovarian activity.     

Discovery of cyclotide-like protein sequences in graminaceous crop plants: ancestral precursors of circular proteins?

Cyclotides are peptides from plants of the Rubiaceae and Violaceae families that have the unusual characteristic of a macrocylic backbone. They are further characterized by their incorporation of a cystine knot in which two disulfides, along with the intervening backbone residues, form a ring through which a third disulfide is threaded. The cyclotides have been found in every Violaceae species screened to date but are apparently present in only a few Rubiaceae species. The selective distribution reported so far raises questions about the evolution of the cyclotides within the plant kingdom. In this study, we use a combined bioinformatics and expression analysis approach to elucidate the evolution and distribution of the cyclotides in the plant kingdom and report the discovery of related sequences widespread in the Poaceae family, including crop plants such as rice (Oryza sativa), maize (Zea mays), and wheat (Triticum aestivum), which carry considerable economic and social importance. The presence of cyclotide-like sequences within these plants suggests that the cyclotides may be derived from an ancestral gene of great antiquity. Quantitative RT-PCR was used to show that two of the discovered cyclotide-like genes from rice and barley (Hordeum vulgare) have tissue-specific expression patterns.     

MM-ChIP enables integrative analysis of cross-platform and between-laboratory ChIP-chip or ChIP-seq data

The ChIP-chip and ChIP-seq techniques enable genome-wide mapping of in vivo protein-DNA interactions and chromatin states. The cross-platform and between-laboratory variation poses a challenge to the comparison and integration of results from different ChIP experiments. We describe a novel method, MM-ChIP, which integrates information from cross-platform and between-laboratory ChIP-chip or ChIP-seq datasets. It improves both the sensitivity and the specificity of detecting ChIP-enriched regions, and is a useful meta-analysis tool for driving discoveries from multiple data sources.     

Heat-induced electrical signals affect cytoplasmic and apoplastic pH as well as photosynthesis during propagation through the maize leaf

Combining measurements of electric potential and pH with such of chlorophyll fluorescence and leaf gas exchange showed heat stimulation to evoke an electrical signal (propagation speed: 3–5 mm s⁻¹) that travelled through the leaf while reducing the net CO₂ uptake rate and the photochemical quantum yield of both photosystems (PS). Two-dimensional imaging analysis of the chlorophyll fluorescence signal of PS II revealed that the yield reduction spread basipetally via the veins through the leaf at a speed of 1.6 ± 0.3 mm s⁻¹ while the propagation speed in the intervein region was c. 50 times slower. Propagation of the signal through the veins was confirmed because PS I, which is present in the bundle sheath cells around the leaf vessels, was affected first. Hence, spreading of the signal along the veins represents a path with higher travelling speed than within the intervein region of the leaf lamina. Upon the electrical signal, cytoplasmic pH decreased transiently from 7.0 to 6.4, while apoplastic pH increased transiently from 4.5 to 5.2. Moreover, photochemical quantum yield of isolated chloroplasts was strongly affected by pH changes in the surrounding medium, indicating a putative direct influence of electrical signalling via changes of cytosolic pH on leaf photosynthesis.     

The Chloroplast and Leaf Developmental Mutant, pale cress, Exhibits Light-conditional Severity and Symptoms Characteristic of its ABA Deficiency

The PALE CRESS gene (PAC) is essential for proper chloroplastand leaf development in Arabidopsis thaliana. The ability ofpac mutants to accumulate significantly more chlorophyll whengrown in low light conditions than in high light conditionssuggests that carotenoid deficiency is at least partly responsiblefor premature cessation of chloroplast development. In additionto accumulation of low levels of chlorophyll and carotenoidpigments,pac mutants are abscisic acid (ABA) deficient and havecharacteristics which may be explained by this deficiency. Theseinclude reduced seed viability and, in enclosed growth conditions,increased leaf growth. Plants transformed with an antisensePAC construct often bear viviparous embryos which may be symptomaticof a deficiency in ABA. Since carotenoids are precursors ofABA, a role for PAC in carotenoid biosynthesis is further supported.The nuclear-encoded, chloroplast-localized PAC protein has beenimplicated in the maturation of plastid-encoded mRNAs. Thus,PAC may affect the abundance of one or more chloroplast proteinswhich function in the synthesis or stability of carotenoids.Using thePROLIFERA gene as a marker for cell division, it isshown that cell division profiles in the pac shoot apex aredisrupted. pac leaves are relatively normal in size and shapedespite the light intensity-induced variability of leaf celldefects. Copyright 2000 Annals of Botany Company Abscisic acid, carotenoid, chloroplast development, leaf development, organismal theory, PALE CRESS,PROLIFERA , vivipary     

Focal adhesion kinase signaling is decreased in polyamine-depleted IEC-6 cells

Polyamines are essential to the migration ofepithelial cells in the intestinal mucosa. Cells depleted of polyaminesdo not attach as rapidly to the extracellular matrix and do not form the actin stress fibers essential for migration. Because both attachment and stress fiber formation depend on integrin signaling andthe formation of focal adhesions, we examined these and related processes in polyamine-depleted IEC-6 cells. There was general decreased tyrosine phosphorylation of focal adhesion kinase (FAK), and,specifically, decreased phosphorylation of Tyr-925, the paxillin binding site. In control cells, FAK phosphorylation was rapid afterattachment to the extracellular matrix, while attached cells depletedof polyamines had significantly delayed phosphorylation. FAK activitywas also significantly inhibited in polyamine-depleted cells as was thephosphorylation of paxillin. Polyamine-depleted cells failed to spreadnormally after attachment, and immunocytochemistry showed littlecolocalization of FAK and actin compared with controls. Focal adhesioncomplex formation was greatly reduced in the absence of polyamines.These data suggest that defective integrin signaling may, at least inpart, account for the decreased rates of attachment, actin stress fiberformation, spreading, and migration observed in polyamine-depleted cells.