European Molecular Biology Laboratory

Microglia are highly motile phagocytic cells that infiltrate and take up residence in the developing brain, where they are thought to provide a surveillance and scavenging function. However, although microglia have been shown to engulf and clear damaged cellular debris after brain insult, it remains less clear what role microglia play in the uninjured brain. Here, we show that microglia actively engulf synaptic material and play a major role in synaptic pruning during postnatal development in mice. These findings link microglia surveillance to synaptic maturation and suggest that deficits in microglia function may contribute to synaptic abnormalities seen in some neurodevelopmental disorders.

Drought and salinity are two widespread environmental conditions leading to low water availability for plants. Low water availability is considered the main environmental factor limiting photosynthesis and, consequently, plant growth and yield worldwide. There has been a long-standing controversy as to whether drought and salt stresses mainly limit photosynthesis through diffusive resistances or by metabolic impairment. Reviewing in vitro and in vivo measurements, it is concluded that salt and drought stress predominantly affect diffusion of CO(2) in the leaves through a decrease of stomatal and mesophyll conductances, but not the biochemical capacity to assimilate CO(2), at mild to rather severe stress levels. The general failure of metabolism observed at more severe stress suggests the occurrence of secondary oxidative stresses, particularly under high-light conditions. Estimates of photosynthetic limitations based on the photosynthetic response to intercellular CO(2) may lead to artefactual conclusions, even if patchy stomatal closure and the relative increase of cuticular conductance are taken into account, as decreasing mesophyll conductance can cause the CO(2) concentration in chloroplasts of stressed leaves to be considerably lower than the intercellular CO(2) concentration. Measurements based on the photosynthetic response to chloroplast CO(2) often confirm that the photosynthetic capacity is preserved but photosynthesis is limited by diffusive resistances in drought and salt-stressed leaves.

Simple sequences are stretches of DNA which consist of only one, or a few tandemly repeated nucleotides, for example poly (dA) X poly (dT) or poly (dG-dT) X poly (dC-dA). These two types of simple sequence have been shown to be repetitive and interspersed in many eukaryotic genomes. Several other types have been found by sequencing eukaryotic DNA. In this report we have undertaken a systematical survey for simple sequences. We hybridized synthetical simple sequence DNA to genome blots of phylogenetically different organisms. We found that many, probably even all possible types of simple sequence are repetitive components of eukaryotic genomes. We propose therefore that they arise by common mechanisms namely slippage replication and unequal crossover and that they might have no general function with regards to gene expression. This latter inference is supported by the fact that we have detected simple sequences only in the metabolically inactive micronucleus of the protozoan Stylonychia, but not in the metabolically active macronucleus which is derived from the micronucleus by chromosome diminution.

We have constructed a series of plasmids, the pEMBL family, characterized by the presence of 1) the bla gene as selectable marker, 2) a short segment coding for the alpha-peptide of beta-galactosidase and containing a multiple cloning sites polylinker, 3) the intragenic region of phage F1. pEMBL plasmids have the property of being encapsidated as single stranded DNA, upon superinfection with phage F1. These vectors have been used successfully for DNA sequencing with the dideoxy-method, and can be used for any other purpose for which M13 derivatives are used. However, the pEMBL plasmids have the advantage of being smaller than M13 vectors, and the purification of the DNA is simpler. In addition, and most importantly, long inserts have a higher stability in pEMBL plasmids than M13 vectors.

Microglia are highly motile glial cells that are proposed to mediate synaptic pruning during neuronal circuit formation. Disruption of signaling between microglia and neurons leads to an excess of immature synaptic connections, thought to be the result of impaired phagocytosis of synapses by microglia. However, until now the direct phagocytosis of synapses by microglia has not been reported and fundamental questions remain about the precise synaptic structures and phagocytic mechanisms involved. Here we used light sheet fluorescence microscopy to follow microglia-synapse interactions in developing organotypic hippocampal cultures, complemented by a 3D ultrastructural characterization using correlative light and electron microscopy (CLEM). Our findings define a set of dynamic microglia-synapse interactions, including the selective partial phagocytosis, or trogocytosis (trogo-: nibble), of presynaptic structures and the induction of postsynaptic spine head filopodia by microglia. These findings allow us to propose a mechanism for the facilitatory role of microglia in synaptic circuit remodeling and maturation.

Macrophages play an essential role in the resolution of tissue damage through removal of necrotic cells, thus paving the way for tissue regeneration. Macrophages also directly support the formation of new tissue to replace the injury, through their acquisition of an anti-inflammatory, or M2, phenotype, characterized by a gene expression program that includes IL-10, the IL-13 receptor, and arginase 1. We report that deletion of two CREB-binding sites from the Cebpb promoter abrogates Cebpb induction upon macrophage activation. This blocks the downstream induction of M2-specific Msr1, Il10, II13ra, and Arg-1 genes, whereas the inflammatory (M1) genes Il1, Il6, Tnfa, and Il12 are not affected. Mice carrying the mutated Cebpb promoter (betaDeltaCre) remove necrotic tissue from injured muscle, but exhibit severe defects in muscle fiber regeneration. Conditional deletion of the Cebpb gene in muscle cells does not affect regeneration, showing that the C/EBPbeta cascade leading to muscle repair is muscle-extrinsic. While betaDeltaCre macrophages efficiently infiltrate injured muscle they fail to upregulate Cebpb, leading to decreased Arg-1 expression. CREB-mediated induction of Cebpb expression is therefore required in infiltrating macrophages for upregulation of M2-specific genes and muscle regeneration, providing a direct genetic link between these two processes.

The choice between double-strand break (DSB) repair by either homology-directed repair (HDR) or nonhomologous end joining (NHEJ) is tightly regulated. Defects in this regulation can induce genome instability and cancer. 53BP1 is critical for the control of DSB repair, promoting NHEJ, and inhibiting the 5' end resection needed for HDR. Using dysfunctional telomeres and genome-wide DSBs, we identify Rif1 as the main factor used by 53BP1 to impair 5' end resection. Rif1 inhibits resection involving CtIP, BLM, and Exo1; limits accumulation of BRCA1/BARD1 complexes at sites of DNA damage; and defines one of the mechanisms by which 53BP1 causes chromosomal abnormalities in Brca1-deficient cells. These data establish Rif1 as an important contributor to the control of DSB repair by 53BP1.

GABA-mediated fast-hyperpolarizing inhibition depends on extrusion of chloride by the neuron-specific K-Cl cotransporter, KCC2. Here we show that sustained interictal-like activity in hippocampal slices downregulates KCC2 mRNA and protein expression in CA1 pyramidal neurons, which leads to a reduced capacity for neuronal Cl- extrusion. This effect is mediated by endogenous BDNF acting on tyrosine receptor kinase B (TrkB), with down-stream cascades involving both Shc/FRS-2 (src homology 2 domain containing transforming protein/FGF receptor substrate 2) and PLCgamma (phospholipase Cgamma)-cAMP response element-binding protein signaling. The plasmalemmal KCC2 has a very high rate of turnover, with a time frame that suggests a novel role for changes in KCC2 expression in diverse manifestations of neuronal plasticity. A downregulation of KCC2 may be a general early response involved in various kinds of neuronal trauma.

A cDNA encoding a protein with 70% amino acid identity to the previously characterized gamma-aminobutyric acidA (GABAA) receptor alpha-subunits was isolated from a rat brain cDNA library by homology screening. As observed for alpha 1-, alpha 2-, and alpha 3-subunits, coexpression of this new alpha-subunit (alpha 5) with a beta- and gamma 2-subunit in cultured cells produces receptors displaying high-affinity binding sites for both muscimol, a GABA agonist, and benzodiazepines. Characteristic of GABAA/benzodiazepine type II sites, receptors containing alpha 2-, alpha 3- or alpha 5-subunits have low affinities for several type I-selective compounds. However, alpha 5-subunit-containing receptors have lower affinities for zolpidem (30-fold) and Cl 218 872 (three-fold) than measured previously using recombinantly expressed type II receptors containing either alpha 2- or alpha 3-subunits. Based on these findings, a reclassification of the GABAA/benzodiazepine receptors is warranted.

Canonical animal microRNAs (miRNAs) are generated by sequential cleavage of precursor substrates by the Drosha and Dicer RNase III enzymes. Several variant pathways exploit other RNA metabolic activities to generate functional miRNAs. However, all of these pathways culminate in Dicer cleavage, suggesting that this is a unifying feature of miRNA biogenesis. Here, we show that maturation of miR-451, a functional miRNA that is perfectly conserved among vertebrates, is independent of Dicer. Instead, structure-function and knockdown studies indicate that Drosha generates a short pre-mir-451 hairpin that is directly cleaved by Ago2 and followed by resection of its 3' terminus. We provide stringent evidence for this model by showing that Dicer knockout cells can generate mature miR-451 but not other miRNAs, whereas Ago2 knockout cells reconstituted with wild-type Ago2, but not Slicer-deficient Ago2, can process miR-451. Finally, we show that the mir-451 backbone is amenable to reprogramming, permitting vector-driven expression of diverse functional miRNAs in the absence of Dicer. Beyond the demonstration of an alternative strategy to direct gene silencing, these observations open the way for transgenic rescue of Dicer conditional knockouts.

Body temperature homeostasis is critical for survival and requires precise regulation by the nervous system. The hypothalamus serves as the principal thermostat that detects and regulates internal temperature. We demonstrate that the ion channel TRPM2 [of the transient receptor potential (TRP) channel family] is a temperature sensor in a subpopulation of hypothalamic neurons. TRPM2 limits the fever response and may detect increased temperatures to prevent overheating. Furthermore, chemogenetic activation and inhibition of hypothalamic TRPM2-expressing neurons in vivo decreased and increased body temperature, respectively. Such manipulation may allow analysis of the beneficial effects of altered body temperature on diverse disease states. Identification of a functional role for TRP channels in monitoring internal body temperature should promote further analysis of molecular mechanisms governing thermoregulation and foster the genetic dissection of hypothalamic circuits involved with temperature homeostasis.

A-reader YTHDF2 is an intrinsic determinant of mammalian oocyte competence and early zygotic development.

Monoamine oxidase A gene (MAOA) has earned the nickname "warrior gene" because it has been linked to aggression in observational and survey-based studies. However, no controlled experimental studies have tested whether the warrior gene actually drives behavioral manifestations of these tendencies. We report an experiment, synthesizing work in psychology and behavioral economics, which demonstrates that aggression occurs with greater intensity and frequency as provocation is experimentally manipulated upwards, especially among low activity MAOA (MAOA-L) subjects. In this study, subjects paid to punish those they believed had taken money from them by administering varying amounts of unpleasantly hot (spicy) sauce to their opponent. There is some evidence of a main effect for genotype and some evidence for a gene by environment interaction, such that MAOA is less associated with the occurrence of aggression in a low provocation condition, but significantly predicts such behavior in a high provocation situation. This new evidence for genetic influences on aggression and punishment behavior complicates characterizations of humans as "altruistic" punishers and supports theories of cooperation that propose mixed strategies in the population. It also suggests important implications for the role of individual variance in genetic factors contributing to everyday behaviors and decisions.

Rationale: Aging represents a major risk factor for coronary artery disease and aortic aneurysm formation. MicroRNAs (miRs) have emerged as key regulators of biological processes, but their role in age-associated vascular pathologies is unknown. Objective: We aim to identify miRs in the vasculature that are regulated by age and play a role in age-induced vascular pathologies. Methods and Results: Expression profiling of aortic tissue of young versus old mice identified several age-associated miRs. Among the significantly regulated miRs, the increased expression of miR-29 family members was associated with a profound downregulation of numerous extracellular matrix (ECM) components in aortas of aged mice, suggesting that this miR family contributes to ECM loss, thereby sensitizing the aorta for aneurysm formation. Indeed, miR-29 expression was significantly induced in 2 experimental models for aortic dilation: angiotensin II-treated aged mice and genetically induced aneurysms in Fibulin-4 R/R mice. More importantly, miR-29b levels were profoundly increased in biopsies of human thoracic aneurysms, obtained from patients with either bicuspid ( n =79) or tricuspid aortic valves ( n =30). Finally, LNA-modified antisense oligonucleotide-mediated silencing of miR-29 induced ECM expression and inhibited angiotensin II-induced dilation of the aorta in mice. Conclusion: In conclusion, miR-29-mediated downregulation of ECM proteins may sensitize the aorta to the formation of aneurysms in advanced age. Inhibition of miR-29 in vivo abrogates aortic dilation in mice, suggesting that miR-29 may represent a novel molecular target to augment matrix synthesis and maintain vascular wall structural integrity.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by a selective degeneration of motor neurons, atrophy, and paralysis of skeletal muscle. Although a significant proportion of familial ALS results from a toxic gain of function associated with dominant SOD1 mutations, the etiology of the disease and its specific cellular origins have remained difficult to define. Here, we show that muscle-restricted expression of a localized insulin-like growth factor (Igf) -1 isoform maintained muscle integrity and enhanced satellite cell activity in SOD1(G93A) transgenic mice, inducing calcineurin-mediated regenerative pathways. Muscle-specific expression of local Igf-1 (mIgf-1) isoform also stabilized neuromuscular junctions, reduced inflammation in the spinal cord, and enhanced motor neuronal survival in SOD1(G93A) mice, delaying the onset and progression of the disease. These studies establish skeletal muscle as a primary target for the dominant action of inherited SOD1 mutation and suggest that muscle fibers provide appropriate factors, such as mIgf-1, for neuron survival.

Variant Creutzfeldt-Jakob disease and bovine spongiform encephalopathy are initiated by extracerebral exposure to prions. Although prion transmission from extracerebral sites to the brain represents a potential target for prophylaxis, attempts at vaccination have been limited by the poor immunogenicity of prion proteins. To circumvent this, we expressed an anti-prion protein (anti-PrP) mu chain in Prnp(o/o) mice. Transgenic mice developed sustained anti-PrP titers, which were not suppressed by introduction of Prnp+ alleles. Transgene expression prevented pathogenesis of prions introduced by intraperitoneal injection in the spleen and brain. Expression of endogenous PrP (PrP(C)) in the spleen and brain was unaffected, suggesting that immunity was responsible for protection. This indicates the feasibility of immunological inhibition of prion disease in vivo.

Aged haematopoietic stem cells (HSCs) generate more myeloid cells and fewer lymphoid cells compared with young HSCs, contributing to decreased adaptive immunity in aged individuals. However, it is not known how intrinsic changes to HSCs and shifts in the balance between biased HSC subsets each contribute to the altered lineage output. Here, by analysing HSC transcriptomes and HSC function at the single-cell level, we identify increased molecular platelet priming and functional platelet bias as the predominant age-dependent change to HSCs, including a significant increase in a previously unrecognized class of HSCs that exclusively produce platelets. Depletion of HSC platelet programming through loss of the FOG-1 transcription factor is accompanied by increased lymphoid output. Therefore, increased platelet bias may contribute to the age-associated decrease in lymphopoiesis.

A simple system has been designed enabling ultrasensitive on-line detection of fluorescently labelled macromolecules, e.g. nucleic acids, proteins and peptides during electrophoretic separations in gels. An important application is the automated DNA sequence determination without radioactivity. Drying of gels, film exposure and handling are not necessary. A sulphydryl containing M13 sequencing primer has been synthesised and end-labelled in a reaction with fluorescein iodoacetamide. This is then used in the dideoxy reactions. In particular no moving parts or complicated software are required for data collection and analysis. Compared to our first automated device detection sensitivity has been improved by a factor of thirty to about 3 X 10(-18) mol per band. The resolution has increased to about 400 bases in 5 hours, with the possibility to read up to about 500 bases when they are properly labelled. Gels shorter than 20 cm may be used for resolution of about 300 bases. The single gel system may be upgraded for simultaneous running and reading of six or ten sequencing samples.

In 2007, the International Knockout Mouse Consortium (IKMC) made the ambitious promise to generate mutations in virtually every protein-coding gene of the mouse genome in a concerted worldwide action. Now, 5 years later, the IKMC members have developed high-throughput gene trapping and, in particular, gene-targeting pipelines and generated more than 17,400 mutant murine embryonic stem (ES) cell clones and more than 1,700 mutant mouse strains, most of them conditional. A common IKMC web portal (www.knockoutmouse.org) has been established, allowing easy access to this unparalleled biological resource. The IKMC materials considerably enhance functional gene annotation of the mammalian genome and will have a major impact on future biomedical research.

The control of motor behavior in animals and humans requires constant adaptation of neuronal networks to signals of various types and strengths. We found that microRNA-128 (miR-128), which is expressed in adult neurons, regulates motor behavior by modulating neuronal signaling networks and excitability. miR-128 governs motor activity by suppressing the expression of various ion channels and signaling components of the extracellular signal-regulated kinase ERK2 network that regulate neuronal excitability. In mice, a reduction of miR-128 expression in postnatal neurons causes increased motor activity and fatal epilepsy. Overexpression of miR-128 attenuates neuronal responsiveness, suppresses motor activity, and alleviates motor abnormalities associated with Parkinson's-like disease and seizures in mice. These data suggest a therapeutic potential for miR-128 in the treatment of epilepsy and movement disorders.