Tubulin is subject to a special cycle of detyrosination͞tyrosination in which the C-terminal tyrosine of ␣-tubulin is cyclically removed by a carboxypeptidase and readded by a tubulin-tyrosine-ligase (TTL). This tyrosination cycle is conserved in evolution, yet its physiological importance is unknown. Here, we find that TTL suppression in mice causes perinatal death. A minor pool of tyrosinated (Tyr-)tubulin persists in TTL null tissues, being present mainly in dividing TTL null cells where it originates from tubulin synthesis, but it is lacking in postmitotic TTL null cells such as neurons, which is apparently deleterious because early death in TTL null mice is, at least in part, accounted for by a disorganization of neuronal networks, including a disruption of the cortico-thalamic loop. Correlatively, cultured TTL null neurons display morphogenetic anomalies including an accelerated and erratic time course of neurite outgrowth and a premature axonal differentiation. These anomalies may involve a mislocalization of CLIP170, which we find lacking in neurite extensions and growth cones of TTL null neurons. Our results demonstrate a vital role of TTL for neuronal organization and suggest a requirement of Tyr-tubulin for proper control of neurite extensions.CLIP170 ͉ tubulin code

Recent evidence suggests that regulatory pathways might control sustained high levels of FOXP3 in regulatory CD4+CD25hi T (Treg) cells. Based on transcriptional profiling of ex vivo activated Treg and helper CD4+CD25− T (Th) cells we have identified GARP (glycoprotein-A repetitions predominant), LGALS3 (lectin, galactoside-binding, soluble, 3) and LGMN (legumain) as novel genes implicated in human Treg cell function, which are induced upon T-cell receptor stimulation. Retroviral overexpression of GARP in antigen-specific Th cells leads to an efficient and stable re-programming of an effector T cell towards a regulatory T cell, which involves up-regulation of FOXP3, LGALS3, LGMN and other Treg-associated markers. In contrast, overexpression of LGALS3 and LGMN enhance FOXP3 and GARP expression, but only partially induced a regulatory phenotype. Lentiviral down-regulation of GARP in Treg cells significantly impaired the suppressor function and was associated with down-regulation of FOXP3. Moreover, down-regulation of FOXP3 resulted in similar phenotypic changes and down-regulation of GARP. This provides compelling evidence for a GARP-FOXP3 positive feedback loop and provides a rational molecular basis for the known difference between natural and transforming growth factor-β induced Treg cells as we show here that the latter do not up-regulate GARP. In summary, we have identified GARP as a key receptor controlling FOXP3 in Treg cells following T-cell activation in a positive feedback loop assisted by LGALS3 and LGMN, which represents a promising new system for the therapeutic manipulation of T cells in human disease.

N-terminally truncated A␤ peptides starting with pyroglutamate (A␤pE3) represent a major fraction of all A␤ peptides in the brain of Alzheimer disease (AD) patients. A␤pE3 has a higher aggregation propensity and stability and shows increased toxicity compared with full-length A␤. In the present work, we generated a novel monoclonal antibody (9D5) that selectively recognizes oligomeric assemblies of A␤pE3 and studied the potential involvement of oligomeric A␤pE3 in vivo using transgenic mouse models as well as human brains from sporadic and familial AD cases. 9D5 showed an unusual staining pattern with almost nondetectable plaques in sporadic AD patients and non-demented controls. Interestingly, in sporadic and familial AD cases prominent intraneuronal and blood vessel staining was observed. Using a novel sandwich ELISA significantly decreased levels of oligomers in plasma samples from patients with AD compared with healthy controls were identified. Moreover, passive immunization of 5XFAD mice with 9D5 significantly reduced overall A␤ plaque load and A␤pE3 levels, and normalized behavioral deficits. These data indicate that 9D5 is a therapeutically and diagnostically effective monoclonal antibody targeting low molecular weight A␤pE3 oligomers. Alzheimer disease (AD)3 represents the most frequent form of dementia and is characterized by the presence of extracellular amyloid plaques composed of amyloid-␤ (A␤) surrounded by dystrophic neurites and neurofibrillary tangles. The discovery that certain early-onset familial forms of AD may be caused by enhanced levels of A␤ peptides have led to the hypothesis that amyloidogenic A␤ is intimately involved in the AD pathogenic process (1). In the past extracellular A␤ has been regarded as the major culprit, whereas more recent evidence now points to toxic effects of A␤ in intracellular compartments (2-3). In addition, other concepts propose that the soluble oligomers and the ␤-sheet containing amyloid fibrils are the toxic forms of A␤ (4 -6). Supporting this notion, it has been demonstrated that soluble oligomeric A␤42, but not plaque-associated A␤, correlates best with cognitive dysfunction in AD (7-8). Oligomers are formed preferentially intracellulary within neuronal processes and synapses rather than extracellularly (9 -10). Besides full-length A␤ peptides starting with an aspartate at position 1, a variety of different N-truncated A␤ peptides have been identified in AD brains. Ragged peptides including phenylalanine at position 4 of A␤ have been reported as early as 1985 by Masters et al. (11). In contrast, no N-terminal sequence could be obtained from cores purified in a sodium dodecyl sulfate-containing buffer, which led to the assumption that the N terminus could be blocked (12-13). The presence of A␤pE3 (N-terminally truncated A␤ starting with pyroglutamate) in AD brain was subsequently shown using mass spectrometry of purified A␤ peptides, explaining at least partially initial difficulties in sequencing A␤ peptides purified from human brain tissue (14). The author...

Small GTPases of the Rab family not only regulate target recognition in membrane traffic but also control other cellular functions such as cytoskeletal transport and autophagy. Here we show that Rab26 is specifically associated with clusters of synaptic vesicles in neurites. Overexpression of active but not of GDP-preferring Rab26 enhances vesicle clustering, which is particularly conspicuous for the EGFP-tagged variant, resulting in a massive accumulation of synaptic vesicles in neuronal somata without altering the distribution of other organelles. Both endogenous and induced clusters co-localize with autophagy-related proteins such as Atg16L1, LC3B and Rab33B but not with other organelles. Furthermore, Atg16L1 appears to be a direct effector of Rab26 and binds Rab26 in its GTP-bound form, albeit only with low affinity. We propose that Rab26 selectively directs synaptic and secretory vesicles into preautophagosomal structures, suggesting the presence of a novel pathway for degradation of synaptic vesicles.DOI: http://dx.doi.org/10.7554/eLife.05597.001

CitationPseudomonas aeruginosa cupA-encoded fimbriae expression is regulated by a GGDEF and EAL Cyclic-diguanylate (c-di-GMP) is a widespread bacterial signal molecule that plays a major role in the modulation of cellular surface components, such as exopolysaccharides and fimbriae, and in the establishment of a sessile life style. Here, we report that intracellular c-di-GMP levels influence cupA encoded fimbriae expression in Pseudomonas aeruginosa. In an autoaggregative P. aeruginosa small colony variant (SCV) CupA fimbriae and the intracellular c-di-GMP concentration were found to be enhanced as compared to the clonal wild-type. The expression of CupA fimbriae were dependent on a functional PA1120 and morA gene both encoding a GGDEF domain. Overexpression of the GGDEF domain protein PA1120 complemented the PA1120 and the morA mutant with respect to CupA fimbriae expression. In agreement with these findings, overexpression of the EAL domain containing phenotypic variance regulator (PvrR) in the SCV resulted in a switch to wild-type colony morphology, a decreased intracellular level of c-di-GMP and reduced cupA fimbriae expression. Although a regulation of cupA encoded fimbriae expression via c-di-GMP was clearly demonstrated, cupA expression is also under transcriptional control that is independent of the global intracellular c-di-GMP levels.

Type II diabetes (T2D) is characterized by diminished insulin production and resistance of cells to insulin. Among others, endoplasmic reticulum (ER) stress is a principal factor contributing to T2D and induces a shift towards a more reducing cellular environment. At the same time, peripheral insulin resistance triggers the over-production of regulatory hormones such as insulin and human islet amyloid polypeptide (hIAPP). We show that the differential aggregation of reduced and oxidized hIAPP assists to maintain the redox equilibrium by restoring redox equivalents. Aggregation thus induces redox balancing which can assist initially to counteract ER stress. Failure of the protein degradation machinery might finally result in β-cell disruption and cell death. We further present a structural characterization of hIAPP in solution, demonstrating that the N-terminus of the oxidized peptide has a high propensity to form an α-helical structure which is lacking in the reduced state of hIAPP. In healthy cells, this residual structure prevents the conversion into amyloidogenic aggregates.

Neurotransmitter uptake into synaptic vesicles is mediated by vesicular neurotransmitter transporters. Although these transporters belong to different families, they all are thought to share a common overall topology with an even number of transmembrane domains. Using epitope-specific antibodies and mass spectrometry we show that the vesicular GABA transporter (VGAT) possesses an uneven number of transmembrane domains, with the N terminus facing the cytoplasm and the C terminus residing in the synaptic vesicle lumen. Antibodies recognizing the C terminus of VGAT (anti-VGAT-C) selectively label GABAergic nerve terminals of live cultured hippocampal and striatal neurons as confirmed by immunocytochemistry and patch-clamp electrophysiology. Injection of fluorochromated anti-VGAT-C into the hippocampus of mice results in specific labeling of GABAergic synapses in vivo. Overall, our data open the possibility of studying novel GABA release sites, characterizing inhibitory vesicle trafficking, and establishing their contribution to inhibitory neurotransmission at identified GABAergic synapses.

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