Two-Photon Transitions in Quadrupolar and Branched Chromophores: Experiment and Theory

We wish to thank Dr. Francesca Terenziani for stimulating discussions, Dr. M. Drobizhev and A. Rebane for suggesting BDPAS as an additional TPEF standard and providing a sample of the material as well as the TPA cross-section data.International audienceA combined experimental and theoretical study is conducted on a series of model compounds in order to assess the combined role of branching and charge symmetry on absorption, photoluminescence, and two-photon absorption (TPA) properties. The main issue of this study is to examine how branching of quadrupolar chomophores can lead to different consequences as compared to branching of dipolar chromophores. Hence, three structurally related π-conjugated quadrupolar chromophores symmetrically substituted with donor end groups and one branched structure built from the assembly of three quadrupolar branches via a common donor moiety are used as model compounds. Their photophysical properties are studied using UV−vis spectroscopy, and the TPA spectra are determined through two-photon excited fluorescence experiments using femtosecond pulses in the 500−1000 nm range. Experimental studies are complemented by theoretical calculations. The applied theoretical methodology is based on time-dependent density functional theory, the Frenkel exciton model, and analysis in terms of the natural transition orbitals of relevant electronic states. Theory reveals that a symmetrical intramolecular charge transfer from the terminal donating groups to the middle of the molecule takes place in all quadrupolar chromophores upon photoexcitation. In contrast, branching via a central electron-donating triphenylamine moiety breaks the quadrupolar symmetry of the branches. Consequently, all Frank−Condon excited states have significant asymmetric multidimensional charge-transfer character upon excitation. Subsequent vibrational relaxation of the branched chromophore in the excited state leads to a localization of the excitation and fluorescence stemming from a single branch. As opposed to what was earlier observed when dipolar chromophores are branched via the same common electron-donating moiety, we find only a slight enhancement of the maximum TPA response of the branched compound with respect to an additive contribution of its quadrupolar branches. In contrast, substantial modifications of the spectral shape are observed. This is attributed to the subtle interplay of interbranch electronic coupling and asymmetry caused by branching

The Chlamydia muridarum plasmid revisited : new insights into growth kinetics.

Background: Research in chlamydial genetics is challenging because of its obligate intracellular developmental cycle. In vivo systems exist that allow studies of different aspects of basic biology of chlamydiae, the murine Chlamydia muridarum model is one of great importance and thus an essential research tool. C. muridarum carries a plasmid that has a role in virulence.  Our aim was to compare and contrast the C. muridarum plasmid-free phenotype with that of a chromosomally isogenic plasmid-bearing strain, through the inclusion phase of the developmental cycle. Methods: We measured infectivity for plasmid bearing and plasmid-cured C. muridarum by inclusion forming assays in McCoy cells and in parallel bacterial chromosome replication by quantitative PCR, throughout the developmental cycle. In addition to these studies, we have carefully monitored chlamydial inclusion formation by confocal microscopy and transmission electron microscopy. A new E.coli/chlamydial shuttle vector (pNigg::GFP) was constructed using standard cloning technology and used to transform C. muridarum for further phenotypic studies. Results: We have advanced the definition of the chlamydial phenotype away from the simple static observation of mature inclusions and redefined the C. muridarum plasmid-based phenotype on growth profile and inclusion morphology. Our observations on the growth properties of plasmid-cured C. muridarum challenge the established interpretations, especially with regard to inclusion growth kinetics. Introduction of the shuttle plasmid pNigg::GFP into plasmid-cured C. muridarum restored the wild-type plasmid-bearing phenotype and confirmed that loss of the plasmid was the sole cause for the changes in growth and chromosomal replication. Conclusions: Accurate growth curves and sampling at multiple time points throughout the developmental cycle is necessary to define plasmid phenotypes.  There are subtle but important (previously unnoticed) differences in the overall growth profile of plasmid-bearing and plasmid-free C. muridarum.  We have proven that the differences described are solely due to the plasmid pNigg

Neurodevelopmental effects of chronic exposure to elevated levels of pro-inflammatory cytokines in a developing visual system

<p>Abstract</p> <p>Background</p> <p>Imbalances in the regulation of pro-inflammatory cytokines have been increasingly correlated with a number of severe and prevalent neurodevelopmental disorders, including autism spectrum disorder, schizophrenia and Down syndrome. Although several studies have shown that cytokines have potent effects on neural function, their role in neural development is still poorly understood. In this study, we investigated the link between abnormal cytokine levels and neural development using the <it>Xenopus laevis </it>tadpole visual system, a model frequently used to examine the anatomical and functional development of neural circuits.</p> <p>Results</p> <p>Using a test for a visually guided behavior that requires normal visual system development, we examined the long-term effects of prolonged developmental exposure to three pro-inflammatory cytokines with known neural functions: interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α. We found that all cytokines affected the development of normal visually guided behavior. Neuroanatomical imaging of the visual projection showed that none of the cytokines caused any gross abnormalities in the anatomical organization of this projection, suggesting that they may be acting at the level of neuronal microcircuits. We further tested the effects of TNF-α on the electrophysiological properties of the retinotectal circuit and found that long-term developmental exposure to TNF-α resulted in enhanced spontaneous excitatory synaptic transmission in tectal neurons, increased AMPA/NMDA ratios of retinotectal synapses, and a decrease in the number of immature synapses containing only NMDA receptors, consistent with premature maturation and stabilization of these synapses. Local interconnectivity within the tectum also appeared to remain widespread, as shown by increased recurrent polysynaptic activity, and was similar to what is seen in more immature, less refined tectal circuits. TNF-α treatment also enhanced the overall growth of tectal cell dendrites. Finally, we found that TNF-α-reared tadpoles had increased susceptibility to pentylenetetrazol-induced seizures.</p> <p>Conclusions</p> <p>Taken together our data are consistent with a model in which TNF-α causes premature stabilization of developing synapses within the tectum, therefore preventing normal refinement and synapse elimination that occurs during development, leading to increased local connectivity and epilepsy. This experimental model also provides an integrative approach to understanding the effects of cytokines on the development of neural circuits and may provide novel insights into the etiology underlying some neurodevelopmental disorders.</p

Detection and correction of underassigned rotational symmetry prior to structure deposition

An X-ray structural model can be reassigned to a higher symmetry space group using the presented framework if its noncrystallographic symmetry operators are close to being exact crystallographic relationships. About 2% of structures in the Protein Data Bank can be reclassified in this way

SHP-1 negatively regulates neuronal survival by functioning as a TrkA phosphatase

Nerve growth factor (NGF) mediates the survival and differentiation of neurons by stimulating the tyrosine kinase activity of the TrkA/NGF receptor. Here, we identify SHP-1 as a phosphotyrosine phosphatase that negatively regulates TrkA. SHP-1 formed complexes with TrkA at Y490, and dephosphorylated it at Y674/675. Expression of SHP-1 in sympathetic neurons induced apoptosis and TrkA dephosphorylation. Conversely, inhibition of endogenous SHP-1 with a dominant-inhibitory mutant stimulated basal tyrosine phosphorylation of TrkA, thereby promoting NGF-independent survival and causing sustained and elevated TrkA activation in the presence of NGF. Mice lacking SHP-1 had increased numbers of sympathetic neurons during the period of naturally occurring neuronal cell death, and when cultured, these neurons survived better than wild-type neurons in the absence of NGF. These data indicate that SHP-1 can function as a TrkA phosphatase, controlling both the basal and NGF-regulated level of TrkA activity in neurons, and suggest that SHP-1 regulates neuron number during the developmental cell death period by directly regulating TrkA activity

Neuron-astrocyte transmitophagy is altered in Alzheimer's disease

Under physiological conditions in vivo astrocytes internalize and degrade neuronal mitochondria in a process called transmitophagy. Mitophagy is widely reported to be impaired in neurodegeneration but it is unknown whether and how transmitophagy is altered in Alzheimer's disease (AD). Here we report that the internalization of neuronal mitochondria is significantly increased in astrocytes isolated from AD mouse brains. We also demonstrate that the degradation of neuronal mitochondria by astrocytes is increased in AD mice at the age of 6 months onwards. Furthermore, we demonstrate for the first time a similar phenomenon between human neurons and AD astrocytes, and in murine hippocampi in vivo. The results suggest the involvement of S100a4 in impaired mitochondrial transfer between neurons and AD astrocytes together with significant increases in the mitophagy regulator and reactive oxygen species in aged AD astrocytes. These findings demonstrate altered neuronsupporting functions of AD astrocytes and provide a starting point for studying the molecular mechanisms of transmitophagy in AD.Peer reviewe

The factor structure of the Forms of Self-Criticising/Attacking & Self-Reassuring Scale in thirteen distinct populations

There is considerable evidence that self-criticism plays a major role in the vulnerability to and recovery from psychopathology. Methods to measure this process, and its change over time, are therefore important for research in psychopathology and well-being. This study examined the factor structure of a widely used measure, the Forms of Self-Criticising/Attacking & Self-Reassuring Scale in thirteen nonclinical samples (N = 7510) from twelve different countries: Australia (N = 319), Canada (N = 383), Switzerland (N = 230), Israel (N = 476), Italy (N = 389), Japan (N = 264), the Netherlands (N = 360), Portugal (N = 764), Slovakia (N = 1326), Taiwan (N = 417), the United Kingdom 1 (N = 1570), the United Kingdom 2 (N = 883), and USA (N = 331). This study used more advanced analyses than prior reports: a bifactor item-response theory model, a two-tier item-response theory model, and a non-parametric item-response theory (Mokken) scale analysis. Although the original three-factor solution for the FSCRS (distinguishing between Inadequate-Self, Hated-Self, and Reassured-Self) had an acceptable fit, two-tier models, with two general factors (Self-criticism and Self-reassurance) demonstrated the best fit across all samples. This study provides preliminary evidence suggesting that this two-factor structure can be used in a range of nonclinical contexts across countries and cultures. Inadequate-Self and Hated-Self might not by distinct factors in nonclinical samples. Future work may benefit from distinguishing between self-correction versus shame-based self-criticism.Peer reviewe

A cellular trafficking signal in the SIV envelope protein cytoplasmic domain is strongly selected for in pathogenic infection

The HIV/SIV envelope glycoprotein (Env) cytoplasmic domain contains a highly conserved Tyr-based trafficking signal that mediates both clathrin-dependent endocytosis and polarized sorting. Despite extensive analysis, the role of these functions in viral infection and pathogenesis is unclear. An SIV molecular clone (SIVmac239) in which this signal is inactivated by deletion of Gly-720 and Tyr-721 (SIVmac239ΔGY), replicates acutely to high levels in pigtail macaques (PTM) but is rapidly controlled. However, we previously reported that rhesus macaques and PTM can progress to AIDS following SIVmac239ΔGY infection in association with novel amino acid changes in the Env cytoplasmic domain. These included an R722G flanking the ΔGY deletion and a nine nucleotide deletion encoding amino acids 734–736 (ΔQTH) that overlaps the rev and tat open reading frames. We show that molecular clones containing these mutations reconstitute signals for both endocytosis and polarized sorting. In one PTM, a novel genotype was selected that generated a new signal for polarized sorting but not endocytosis. This genotype, together with the ΔGY mutation, was conserved in association with high viral loads for several months when introduced into naïve PTMs. For the first time, our findings reveal strong selection pressure for Env endocytosis and particularly for polarized sorting during pathogenic SIV infection in vivo