Bla Activity Research Articles

The amygdala-ventral pallidum pathway contributes to a hypodopaminergic state in the ventral tegmental area during protracted abstinence from chronic cocaine.

Incubation of craving, the progressive increase in drug seeking over the first weeks of abstinence, is associated with temporal changes during abstinence in the activity of several structures involved in drug-seeking behaviour. Decreases of dopamine (DA) release and DA neuronal activity (hypodopaminergic state) have been reported in the ventral tegmental area (VTA) during cocaine abstinence, but the mechanisms underlying these neuroadaptations are not well understood. We investigated the potential involvement of a VTA inhibiting circuit (basolateral amygdala [BLA]-ventral pallidum [VP] pathway) in the hypodopaminergic state associated with abstinence from chronic cocaine. In a model of cocaine self-administration, we performed in vivo electrophysiological recordings of DA VTA neurons and BLA neurons from anaesthetised rats during early and protracted abstinence and evaluated the involvement of the BLA-VP pathway using a pharmacological approach. We found significant decreases in VTA DA population activity and significant increases in BLA activity after protracted but not after short-term abstinence from chronic cocaine. The decrease in VTA DA activity was restored by pharmacological inhibition of the activity of either the BLA or the VP, suggesting that these regions exert a negative influence on DA activity. Our study sheds new lights on neuroadaptations occurring during incubation of craving leading to relapse. In particular, we describe the involvement of the BLA-VP pathway in cocaine-induced decreases of DA activity in the VTA. This study adds important information about the specific brain network dysfunctions underlying hypodopaminergic activity during abstinence.

Selective inhibitory control of pyramidal neuron ensembles and cortical subnetworks by chandelier cells.

The neocortex comprises multiple information processing streams mediated by subsets of glutamatergic pyramidal cells (PCs) that receive diverse inputs and project to distinct targets. How GABAergic interneurons regulate the segregation and communication among intermingled PC subsets that contribute to separate brain networks remains unclear. Here we demonstrate that a subset of GABAergic chandelier cells (ChCs) in the prelimbic cortex (PL), which innervate PCs at spike initiation site, selectively control PCs projecting to the basolateral amygdala (BLAPC) compared to those projecting to contralateral cortex (CCPC). These ChCs in turn receive preferential input from local and contralateral CCPCs as opposed to BLAPCs and BLA neurons (the PL-BLA network). Accordingly, optogenetic activation of ChCs rapidly suppresses BLAPCs and BLA activity in freely behaving mice. Thus, the exquisite connectivity of ChCs not only mediates directional inhibition between local PC ensembles but may also shape communication hierarchies between global networks.

An att site-based recombination reporter system for genome engineering and synthetic DNA assembly

BackgroundDirect manipulation of the genome is a widespread technique for genetic studies and synthetic biology applications. The tyrosine and serine site-specific recombination systems of bacteriophages HK022 and ΦC31 are widely used for stable directional exchange and relocation of DNA sequences, making them valuable tools in these contexts. We have developed site-specific recombination tools that allow the direct selection of recombination events by embedding the attB site from each system within the β-lactamase resistance coding sequence (bla).ResultsThe HK and ΦC31 tools were developed by placing the attB sites from each system into the signal peptide cleavage site coding sequence of bla. All possible open reading frames (ORFs) were inserted and tested for recombination efficiency and bla activity. Efficient recombination was observed for all tested ORFs (3 for HK, 6 for ΦC31) as shown through a cointegrate formation assay. The bla gene with the embedded attB site was functional for eight of the nine constructs tested.ConclusionsThe HK/ΦC31 att-bla system offers a simple way to directly select recombination events, thus enhancing the use of site-specific recombination systems for carrying out precise, large-scale DNA manipulation, and adding useful tools to the genetics toolbox. We further show the power and flexibility of bla to be used as a reporter for recombination.

Preferential recruitment of the basolateral amygdala during memory encoding of negative scenes in posttraumatic stress disorder

Background: The vast majority of functional neuroimaging studies in posttraumatic stress disorder (PTSD) have examined the amygdala as a unitary structure. However, an emerging body of studies indicates that separable functions are subserved by discrete amygdala subregions. The basolateral subdivision (BLA), as compared with the centromedial amygdala (CMA), plays a unique role in learning and memory-based processes for threatening events, and alterations to the BLA have been implicated in the pathogenesis of PTSD. We assessed whether PTSD is associated with differential involvement of the BLA versus the CMA during successful encoding of emotionally charged events. Methods: Participants with PTSD (n=11) and a trauma-exposed comparison (TEC) group (n=11) viewed a series of photos that varied in valence (negative versus positive) and arousal (high versus low) while undergoing functional magnetic resonance imaging (fMRI). Subsequently, participants completed an old/new recognition memory test. Results: Using analytic methods based on probabilistic cytoarchitectonic mapping, PTSD was associated with greater activation of the BLA, as compared to the CMA, during successful encoding of negative scenes, a finding which was not observed in the TEC group. Moreover, this memory-related activity in the BLA independently predicted PTSD status. Contrary to hypotheses, there was no evidence of altered BLA activity during memory encoding of high arousing relative to low arousing scenes. Conclusions: Task-related brain activation in PTSD does not appear to be consistent across the entire amygdala. Importantly, memory-related processing of negative information in PTSD is associated with preferential recruitment of the BLA.

Distinct roles of the repeat-containing regions and effector domains of the Vibrio vulnificus multifunctional-autoprocessing repeats-in-toxin (MARTX) toxin.

ABSTRACTVibrio vulnificus is a seafood-borne pathogen that destroys the intestinal epithelium, leading to rapid bacterial dissemination and death. The most important virulence factor is the multifunctional-autoprocessing repeats-in-toxin (MARTX) toxin comprised of effector domains in the center region flanked by long repeat-containing regions which are well conserved among MARTX toxins and predicted to translocate effector domains. Here, we examined the role of the repeat-containing regions using a modified V. vulnificus MARTX (MARTXVv) toxin generated by replacing all the internal effector domains with β-lactamase (Bla). Bla activity was detected in secretions from the bacterium and also in the cytosol of intoxicated epithelial cells. The modified MARTXVv toxin without effector domains retained its necrotic activity but lost its cell-rounding activity. Further, deletion of the carboxyl-terminal repeat-containing region blocked toxin secretion from the bacterium. Deletion of the amino-terminal repeat-containing region had no effect on secretion but completely abolished translocation and necrosis. Neither secretion nor translocation was affected by enzymatically inactivating the cysteine protease domain of the toxin. These data demonstrate that the amino-terminal and carboxyl-terminal repeat-containing regions of the MARTXVv toxin are necessary and sufficient for the delivery of effector domains and epithelial cell lysis in vitro but that effector domains are required for other cytopathic functions. Furthermore, Ca2+-dependent secretion of the modified MARTXVv toxin suggests that nonclassical RTX-like repeats found in the carboxyl-terminal repeat-containing region are functionally similar to classical RTX repeats found in other RTX proteins.

Amygdala perfusion is predicted by its functional connectivity with the ventromedial prefrontal cortex and negative affect.

BackgroundPrevious studies have shown that the activity of the amygdala is elevated in people experiencing clinical and subclinical levels of anxiety and depression (negative affect). It has been proposed that a reduction in inhibitory input to the amygdala from the prefrontal cortex and resultant over-activity of the amygdala underlies this association. Prior studies have found relationships between negative affect and 1) amygdala over-activity and 2) reduced amygdala-prefrontal connectivity. However, it is not known whether elevated amygdala activity is associated with decreased amygdala-prefrontal connectivity during negative affect states.MethodsHere we used resting-state arterial spin labeling (ASL) and blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) in combination to test this model, measuring the activity (regional cerebral blood flow, rCBF) and functional connectivity (correlated fluctuations in the BOLD signal) of one subregion of the amygdala with strong connections with the prefrontal cortex, the basolateral nucleus (BLA), and subsyndromal anxiety levels in 38 healthy subjects.ResultsBLA rCBF was strongly correlated with anxiety levels. Moreover, both BLA rCBF and anxiety were inversely correlated with the strength of the functional coupling of the BLA with the caudal ventromedial prefrontal cortex. Lastly, BLA perfusion was found to be a mediator of the relationship between BLA-prefrontal connectivity and anxiety.ConclusionsThese results show that both perfusion of the BLA and a measure of its functional coupling with the prefrontal cortex directly index anxiety levels in healthy subjects, and that low BLA-prefrontal connectivity may lead to increased BLA activity and resulting anxiety. Thus, these data provide key evidence for an often-cited circuitry model of negative affect, using a novel, multi-modal imaging approach.

Comparison of Two Homogeneous Cell-Based Kinase Assays for JAK2 V617F: SureFire pSTAT5 and GeneBLAzer Fluorescence Resonance Energy Transfer Assays

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway plays an important role in cellular responses to cytokines and growth factors. Recent studies have identified a recurrent somatic activating mutation (JAK2 V617F) in majority of patients with myeloproliferative disorders (MPDs). Development of drugs that target JAK2 V617F is, therefore, of therapeutic relevance. To discover small molecule inhibitors for this target, robust and reliable cell-based assays are important. Here, we present a comparison of two homogeneous, 384-well plate-based cellular assays using Invitrogen's CellSensor® JAK2 V617F interferon regulatory factor-1 (irf1)-beta-lactamase (bla) human erythroleukemia line (HEL): (1) SureFire® pSTAT5 AlphaScreen® assay from PerkinElmer; and (2) GeneBLAzer® fluorescence resonance energy transfer assay from Invitrogen. HEL cells are growth factor-independent due to JAK2 V617F mutation that causes constitutive STAT5 activation. The SureFire assay measures levels of phosphorylated STAT5 downstream of JAKs, while the GeneBLAzer assay is a reporter assay that monitors bla activity further downstream of STAT5. Evaluation of a number of chemically diverse JAK2 inhibitors in the two cellular assays yielded comparable half-maximal inhibitory concentration (IC₅₀) values, boding well for the utility of these assay formats in compound profiling.

An enzymatic virus-like particle assay for sensitive detection of virus entry

A viral entry assay where a beta-lactamase reporter protein fused to the influenza matrix protein-1 (BlaM1) is packaged as a structural component into influenza virus-like particles (VLPs) is described. The Bla reporter is released upon fusion with target cells and can be detected in live cells by flow cytometry, microscopy, or fluorometric plate reader for utility in high-throughput screening approaches. The production of BlaM1 VLPs and subsequent transfer of Bla activity to target cells requires the presence of influenza hemagglutinin (HA) and neuraminidase (NA). In addition, transfer of Bla by the VLPs can be blocked by an influenza neutralizing antibody, is impeded by a chemical inhibitor of influenza virus entry, and requires HA that is cleaved by a protease specific for its cleavage site. An analogous VLP system also was developed for Ebola (EBOV) and Marburg (MARV) viruses, demonstrating that this straightforward assay has broad application for studying the entry steps of enveloped viruses, especially those that require high levels of biosafety containment.

Peripheral anxiogenic drug injections differentially affect cognitive and habit memory: role of basolateral amygdala

Findings from single-solution plus-maze tasks that require the use of either place or response learning indicate that post-training intra-basolateral amygdala (BLA) administration of the anxiogenic α-2 adrenoreceptor antagonist RS 79948 can both enhance dorsal striatal-dependent response learning and impair hippocampus-dependent place learning. Whether post-training peripheral administration of RS 79948 can also enhance and impair response and place learning respectively, is not known. If peripheral drug administration can also produce this “dual” effect on cognitive and habit memory, it would be of interest to know whether the functional integrity of the BLA is critical. In order to examine these questions, the present experiments combined peripheral administration of RS 79948 with concurrent neural inactivation of the BLA. Adult male Long–Evans rats were trained in place or response learning tasks in a water plus-maze. On days 1–3 of training, rats received post-training peripheral injections of saline or RS 79948 (0.1 mg/kg) combined with intra-BLA injections of saline or the sodium channel blocker bupivacaine (1.0% solution, 0.5 μl). Post-training peripheral injections of RS 79948 enhanced acquisition of response learning, and impaired acquisition of place learning. Bupivacaine infusions into the BLA had no effect on acquisition of either task. However, intra-BLA infusions of bupivacaine blocked both the enhancement of response learning and the impairment of place learning produced by RS 79948. Taken together, the findings indicate that although the functional integrity of BLA is not necessary for acquisition of place and response learning, BLA activity is critical in order for peripheral injections of an anxiogenic drug to differentially modulate hippocampus-dependent and dorsal striatal-dependent memory.

Colorimetric screening of bacterial enzyme activity and inhibition based on the aggregation of gold nanoparticles

A simple and novel gold nanoparticle (Au-NPs) based colorimetric method has been developed for efficient screening of class A beta-lactamase (Bla) activity and inhibitors in vitro and in bacterial strains.

The basolateral amygdala modulates specific sensory memory representations in the cerebral cortex

Stress hormones released by an experience can modulate memory strength via the basolateral amygdala, which in turn acts on sites of memory storage such as the cerebral cortex [McGaugh, J. L. (2004). The amygdala modulates the consolidation of memories of emotionally arousing experiences. Annual Review of Neuroscience, 27, 1–28]. Stimuli that acquire behavioral importance gain increased representation in the cortex. For example, learning shifts the tuning of neurons in the primary auditory cortex (A1) to the frequency of a conditioned stimulus (CS), and the greater the level of CS importance, the larger the area of representational gain [Weinberger, N. M. (2007). Associative representational plasticity in the auditory cortex: A synthesis of two disciplines. Learning & Memory, 14(1–2), 1–16]. The two lines of research suggest that BLA strengthening of memory might be accomplished in part by increasing the representation of an environmental stimulus. The present study investigated whether stimulation of the BLA can affect cortical memory representations. In male Sprague–Dawley rats studied under urethane general anesthesia, frequency receptive fields were obtained from A1 before and up to 75 min after the pairing of a tone with BLA stimulation (BLAstm: 100 trials, 400 ms, 100 Hz, 400 μA [±16.54]). Tone started before and continued after BLAstm. Group BLA/1.0 ( n = 16) had a 1 s CS–BLAstm interval while Group BLA/1.6 ( n = 5) has a 1.6 s interval. The BLA/1.0 group did develop specific tuning shifts toward and to the CS, which could change frequency tuning by as much as two octaves. Moreover, its shifts increased over time and were enduring, lasting 75 min. However, group BLA/1.6 did not develop tuning shifts, indicating that precise CS–BLAstm timing is important in the anesthetized animal. Further, training in the BLA/1.0 paradigm but stimulating outside of the BLA did not produce tuning shifts. These findings demonstrate that the BLA is capable of exerting highly specific, enduring, learning-related modifications of stimulus representation in the cerebral cortex. These findings suggest that the ability of the BLA to alter specific cortical representations may underlie, at least in part, the modulatory influence of BLA activity on strengthening long-term memory.

High level heterologous protein production in Lactococcus and Lactobacillus using a new secretion system based on the Lactobacillus brevis S-layer signals

A secretion cassette, based on the expression and secretion signals of a S-layer protein (SlpA) from Lactobacillus brevis, was constructed. E. coli β-lactamase (Bla) was used as the reporter protein to determine the functionality of the S-layer signals for heterologous expression and secretion in Lactococcus lactis, Lactobacillus brevis, Lactobacillus plantarum, Lactobacillus gasseri and Lactobacillus casei using a low-copy-number plasmid derived from pGK12. In all hosts tested, the bla gene was expressed under the slpA signals and all Bla activity was secreted to the culture medium. The Lb. brevis S-layer promoters were very efficiently recognized in L. lactis, Lb. brevis and Lb. plantarum, whereas in Lb. gasseri the slpA promoter region appeared to be recognized at a lower level and in Lb. casei the level of transcripts was below the detection limit. The production of Bla was mainly restricted to the exponential phase of growth. The highest yield of Bla was obtained with L. lactis and Lb. brevis. Without pH control, substantial degradation of Bla occurred during prolonged cultivations with all lactic acid bacteria (LAB) tested. When growing L. lactis and Lb. brevis under pH control, the Bla activity could be stabilized also at the stationary phase. L. lactis produced up to 80 mg/l of Bla which to our knowledge represents the highest amount of a heterologous protein secreted by LAB so far. The short production phase implied a very high rate of secretion with a calculated value of 5×10 5 Bla molecules/cell per h. Such a high rate was also observed with Lb. plantarum, whereas in Lb. brevis the competition between the wild type slpA gene and the secretion construct probably lowered the rate of Bla production. The results obtained indicate wide applicability of the Lb. brevis slpA signals for efficient protein production and secretion in LAB.

Regulation of the protein A-encoding gene in Staphylococcus aureus

The synthesis of several exoproteins, including protein A (SpA) in Staphylococcus aureus is coordinately regulated by the agr locus. Different constructs of the SpA-encoding gene ( spa) were introduced into Agr + and Agr − derivatives of a spa − strain of S. aureus. Plasmid-located spa with deletions at the 3′ end expressed a truncated SpA which was almost exclusively extracellular and which confirmed the role of C-terminal region X in cell-wall binding. In the Agr − host, the production of SpA was elevated severalfold. Transcriptional and translational fusions were constructed to study the agr-mediated regulation of spa gene expression. Translational fusions of a β-lactamase (Bla)-encoding Ap R reporter gene with the spa promoter and N-terminal coding sequences expressed elevated levels of Bla activity in the Agr − host. In contrast, a transcriptional fusion of the spa gene with a promoter of the positively regulated staphylococcal epidermolytic toxin A (ETA)-encoding gene synthesized higher levels of SpA in an Agr + host, as compared to Agr −. Moreover, the synthesis of SpA in the Agr + strain was switched on during the transition from the exponential to stationary phase in a similar fashion to ETA itself. These data strongly indicate that the regulation of both SpA and ETA occurs at the transcriptional level in S. aureus. The agr-regulated spa promoter was defined by deletion analysis and by transcript mapping.

Effect of Growth Temperature on the Production of Bacterial .BETA.-Lactamase in Yeast Cells.

The stability of bacterial β-Lactamase (bla) in Saccharomyces cerevisiae containing YEp vector was monitored at different temperatures. It was found that in all runs the loss of bla activity occurred during the late logarithmic-growth phase. This loss was activated at relatively high temperatures. A transient decrease in cell doublings was observed at the beginning of loss of bla activity, which is followed by approximately one doubling before the end of batch growth. This would appear to indicate that the loss of bla activity is closely related to growth regulation mechanisms of S. cerevisiae cells.

Development of an inducible and enhancible expression and secretion system in Bacillus subtilis

A set of inducible secretion vectors has been developed in Bacillus subtilis based on the regulatory region and the signal peptide sequence of the sacB gene encoding an extracellular enzyme, levansucrase. The expression of the inserted foreign gene ( bla) encoding TEM β-lactamase (Bla), can be induced by the addition of sucrose to the medium. Either the installation of a sacQ expression cassette into the same secretion vector, or the use of a sacU h two-protease-deficient strain (WB30), can significantly enhance expression of the bla gene. However, the combined use of the sacQ-containing secretion vector and the WB30 strain results in no further increase in Bla activity. During development of the secretion vector, the nucleotide sequence around the signal peptidase cleavage site has been redesigned, so that unique restriction sites were installed to facilitate the insertion of foreign genes.

Measurement of cat expression from growth-rate-regulated promoters employing β-lactamase activity as an indicator of plasmid copy number

Many promoter-fusion vectors contain an intact β-lactamase (BLA) gene ( bla) to allow measurement of BLA activity as an internal control for plasmid copy number. This approach rests on the assumption that bla is constitutively expressed. To use such vectors for comparison of promoter activity at different growth rates it was necessary to confirm that this is the case under all physiological conditions. The relationship between plasmid copy number and BLA activity at different steady-state growth rates in Escherichia coli HB101 transformed with a ColE1-type plasmid (pBR325) was examined. Both BLA activity and plasmid copy number decreased in a parallel fashion as growth rate increased. This finding was tested further by measuring the growth-rate-regulated expression of the chloramphenicol acetyltransferase (CAT) gene under the control of the rrnB P1 promoter in a plasmid pKK231-1 fusion. The results indicate that BLA activity is a reliable indicator of copy number at a wide range of growth rates and that CAT/BLA ratios can be employed as a valid measure of promoter-specific activity in such plasmid fusions under these different physiological conditions.

Synthesis of the nutL DNA segments and analysis of antitermination and termination functions in coliphage lambda

The nut antiterminator sequence, when present between a promoter and a terminator, permits the N-mediated antitermination of transcription in phage λ. The efficiency of nutL was determined by assaying the activity of gene galK placed on a plasmid downstream from the promoter, nutL and terminator modules. As a reference and an estimate of the plasmid copy number, we have used an improved and very reproducible assay for bla activity. Sequences consisting of the 17-bp nutL core flanked by two HindIII cohesive sites were synthesized by the phosphite coupling method, and cloned in proper orientation between the pp promoter of pBR322 and λ gene N followed by the t L1 terminator on a galK-expression plasmid. The antitermination efficiencies for two synthetic 17-bp nutL sequences, one wild type and one point mutant at the base of the nutL stem, are similar but substantially reduced in comparison with the native 25-bp nutL sequence cloned at the same site in the otherwise identical galK-expression plasmid. Multiple tandem insertions of the synthetic 17-bp nutL segment successively increase antitermination efficiency, but also to levels below those of comparable plasmids carrying multiple copies of the native 25-bp nutL sequence. Thus, several specific base pairs in the flanking sequences appear to be important for the efficient nut function. In an inverted orientation the 17-bp nutL sequence has lost its antitermination function. It also lost the termination activity exhibited by inversion of the longer 25-bp and 74-bp native nutL sequences.