| 1. |
- Noborn, Fredrik, et al.
(författare)
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Role of neurexin heparan sulfate in the molecular assembly of synapses - Expanding the neurexin code?
- 2023
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Ingår i: Febs Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 290:3, s. 252-265
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Tidskriftsartikel (refereegranskat)abstract
- Synapses are the minimal information processing units of the brain and come in many flavors across distinct circuits. The shape and properties of a synapse depend on its molecular organisation, which is thought to largely depend on interactions between cell adhesion molecules across the synaptic cleft. An established example is that of presynaptic neurexins and their interactions with structurally diverse postsynaptic ligands: the diversity of neurexin isoforms that arise from alternative promoters and alternative splicing specify synaptic properties by dictating ligand preference. The recent finding that a majority of neurexin isoforms exist as proteoglycans with a single heparan sulfate (HS) polysaccharide adds to this complexity. Sequence motifs within the HS polysaccharide may differ between neuronal cell types to contribute specificity to its interactions, thereby expanding the coding capacity of neurexin diversity. However, an expanding number of HS-binding proteins have been found capable to recruit neurexins via the HS chain, challenging the concept of a code provided by neurexin splice isoforms. Here we discuss the possible roles of the neurexin HS in light of what is known from other HS-protein interactions, and propose a model for how the neurexin HS polysaccharide may contribute to synaptic assembly. We also discuss how the neurexin HS may be regulated by co-secreted carbonic anhydrase-related and FAM19A proteins, and highlight some key issues that should be resolved to advance the field.
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| 2. |
- Kim, H., et al.
(författare)
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Calsyntenin-3 interacts with both ?- and ?-neurexins in the regulation of excitatory synaptic innervation in specific Schaffer collateral pathways
- 2020
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Ingår i: Journal of Biological Chemistry. - 0021-9258. ; 295:27, s. 9244-9262
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Tidskriftsartikel (refereegranskat)abstract
- Calsyntenin-3 (Clstn3) is a postsynaptic adhesion molecule that induces presynaptic differentiation via presynaptic neurexins (Nrxns), but whether Nrxns directly bind to Clstn3 has been a matter of debate. Here, using LC?MS/MS?based protein analysis, confocal microscopy, RNAscope assays, and electrophysiological recordings, we show that ?-Nrxns directly interact via their LNS domain with Clstn3 and Clstn3 cadherin domains. Expression of splice site 4 (SS4) insert?positive ?-Nrxn variants, but not insert?negative variants, reversed the impaired Clstn3 synaptogenic activity observed in Nrxn-deficient neurons. Consistently, Clstn3 selectively formed complexes with SS4?positive Nrxnsin vivo. Neuron-specific Clstn3 deletion caused significant reductions in number of excitatory synaptic inputs. Moreover, expression of Clstn3 cadherin domains in CA1 neurons of Clstn3 conditional knockout mice rescued structural deficits in excitatory synapses, especially within the stratum radiatum layer. Collectively, our results suggest that Clstn3 links to SS4?positive Nrxns to induce presynaptic differentiation and orchestrate excitatory synapse development in specific hippocampal neural circuits, including Schaffer collateral afferents.
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| 3. |
- Marco de La Cruz, Berta, 1990, et al.
(författare)
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Liprin-α proteins are master regulators of human presynapse assembly
- 2024
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Ingår i: NATURE NEUROSCIENCE. - 1097-6256 .- 1546-1726.
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Tidskriftsartikel (refereegranskat)abstract
- The formation of mammalian synapses entails the precise alignment of presynaptic release sites with postsynaptic receptors but how nascent cell-cell contacts translate into assembly of presynaptic specializations remains unclear. Guided by pioneering work in invertebrates, we hypothesized that in mammalian synapses, liprin-alpha proteins directly link trans-synaptic initial contacts to downstream steps. Here we show that, in human neurons lacking all four liprin-alpha isoforms, nascent synaptic contacts are formed but recruitment of active zone components and accumulation of synaptic vesicles is blocked, resulting in 'empty' boutons and loss of synaptic transmission. Interactions with presynaptic cell adhesion molecules of either the LAR-RPTP family or neurexins via CASK are required to localize liprin-alpha to nascent synaptic sites. Liprin-alpha subsequently recruits presynaptic components via a direct interaction with ELKS proteins. Thus, assembly of human presynaptic terminals is governed by a hierarchical sequence of events in which the recruitment of liprin-alpha proteins by presynaptic cell adhesion molecules is a critical initial step. This paper identifies the evolutionarily conserved liprin-alpha protein family as key mediators of presynaptic assembly in human neurons. Their recruitment to sites formed by contacting neurons is the critical initial step that triggers presynaptic differentiation.
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| 4. |
- Montoliu-Gaya, Laia, et al.
(författare)
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CA10 regulates neurexin heparan sulfate addition via a direct binding in the secretory pathway
- 2021
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Ingår i: Embo Reports. - : EMBO. - 1469-221X .- 1469-3178. ; 22:4
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Tidskriftsartikel (refereegranskat)abstract
- Neurexins are presynaptic adhesion molecules that shape the molecular composition of synapses. Diversification of neurexins in numerous isoforms is believed to confer synapse-specific properties by engaging with distinct ligands. For example, a subset of neurexin molecules carry a heparan sulfate (HS) glycosaminoglycan that controls ligand binding, but how this post-translational modification is controlled is not known. Here, we observe that CA10, a ligand to neurexin in the secretory pathway, regulates neurexin-HS formation. CA10 is exclusively found on non-HS neurexin and CA10 expressed in neurons is sufficient to suppress HS addition and attenuate ligand binding and synapse formation induced by ligands known to recruit HS. This effect is mediated by a direct interaction in the secretory pathway that blocks the primary step of HS biosynthesis: xylosylation of the serine residue. NMR reveals that CA10 engages residues on either side of the serine that can be HS-modified, suggesting that CA10 sterically blocks xylosyltransferase access in Golgi. These results suggest a mechanism for the regulation of HS on neurexins and exemplify a new mechanism to regulate site-specific glycosylations.
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| 5. |
- Oldfors Hedberg, Carola, 1969, et al.
(författare)
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Ribonuclease inhibitor 1 (RNH1) deficiency cause congenital cataracts and global developmental delay with infection-induced psychomotor regression and anemia
- 2023
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Ingår i: European Journal of Human Genetics. - : Springer Science and Business Media LLC. - 1018-4813 .- 1476-5438.
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Tidskriftsartikel (refereegranskat)abstract
- Ribonuclease inhibitor 1, also known as angiogenin inhibitor 1, encoded by RNH1, is a ubiquitously expressed leucine-rich repeat protein, which is highly conserved in mammalian species. Inactivation of rnh1 in mice causes an embryonically lethal anemia, but the exact biological function of RNH1 in humans remains unknown and no human genetic disease has so far been associated with RNH1. Here, we describe a family with two out of seven siblings affected by a disease characterized by congenital cataract, global developmental delay, myopathy and psychomotor deterioration, seizures and periodic anemia associated with upper respiratory tract infections. A homozygous splice-site variant (c.615-2A > C) in RNH1 segregated with the disease. Sequencing of RNA derived from patient fibroblasts and cDNA analysis of skeletal muscle mRNA showed aberrant splicing with skipping of exon 7. Western blot analysis revealed a total lack of the RNH1 protein. Functional analysis revealed that patient fibroblasts were more sensitive to RNase A exposure, and this phenotype was reversed by transduction with a lentivirus expressing RNH1 to complement patient cells. Our results demonstrate that loss-of-function of RNH1 in humans is associated with a multiorgan developmental disease with recessive inheritance. It may be speculated that the infection-induced deterioration resulted from an increased susceptibility toward extracellular RNases and/or other inflammatory responses normally kept in place by the RNase inhibitor RNH1.
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| 6. |
- Parra Bravo, Celeste, et al.
(författare)
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Human iPSC 4R tauopathy model uncovers modifiers of tau propagation.
- 2024
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Ingår i: Cell. - 1097-4172.
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Tidskriftsartikel (refereegranskat)abstract
- Tauopathies are age-associated neurodegenerative diseases whose mechanistic underpinnings remain elusive, partially due to a lack of appropriate human models. Here, we engineered human induced pluripotent stem cell (hiPSC)-derived neuronal lines to express 4R Tau and 4R Tau carrying the P301S MAPT mutation when differentiated into neurons. 4R-P301S neurons display progressive Tau inclusions upon seeding with Tau fibrils and recapitulate features of tauopathy phenotypes including shared transcriptomic signatures, autophagic body accumulation, and reduced neuronal activity. A CRISPRi screen of genes associated with Tau pathobiology identified over 500 genetic modifiers of seeding-induced Tau propagation, including retromer VPS29 and genes in the UFMylation cascade. In progressive supranuclear palsy (PSP) and Alzheimer's Disease (AD) brains, the UFMylation cascade is altered in neurofibrillary-tangle-bearing neurons. Inhibiting the UFMylation cascade invitro and invivo suppressed seeding-induced Tau propagation. This model provides a robust platform to identify novel therapeutic strategies for 4R tauopathy.
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| 7. |
- Sofou, Kalliopi, et al.
(författare)
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Bi-allelic VPS16 variants limit HOPS/CORVET levels and cause a mucopolysaccharidosis-like disease.
- 2021
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Ingår i: EMBO molecular medicine. - : EMBO. - 1757-4684 .- 1757-4676. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Lysosomal storage diseases, including mucopolysaccharidoses, result from genetic defects that impair lysosomal catabolism. Here, we describe two patients from two independent families presenting with progressive psychomotor regression, delayed myelination, brain atrophy, neutropenia, skeletal abnormalities, and mucopolysaccharidosis-like dysmorphic features. Both patients were homozygous for the same intronic variant in VPS16, a gene encoding a subunit of the HOPS and CORVET complexes. The variant impaired normal mRNA splicing and led to an ~85% reduction in VPS16 protein levels in patient-derived fibroblasts. Levels of other HOPS/CORVET subunits, including VPS33A, were similarly reduced, but restored upon re-expression of VPS16. Patient-derived fibroblasts showed defects in the uptake and endosomal trafficking of transferrin as well as accumulation of autophagosomes and lysosomal compartments. Re-expression of VPS16 rescued the cellular phenotypes. Zebrafish with disrupted vps16 expression showed impaired development, reduced myelination, and a similar accumulation of lysosomes and autophagosomes in the brain, particularly in glia cells. This disorder resembles previously reported patients with mutations in VPS33A, thus expanding the family of mucopolysaccharidosis-like diseases that result from mutations in HOPS/CORVET subunits.
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| 8. |
- Zhao, Hongxing, et al.
(författare)
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Detection of SARS-CoV-2 antibodies in serum and dried blood spot samples of vaccinated individuals using a sensitive homogeneous proximity extension assay.
- 2022
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Ingår i: New biotechnology. - : Elsevier BV. - 1871-6784 .- 1876-4347. ; 72, s. 139-148
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Tidskriftsartikel (refereegranskat)abstract
- A homogeneous PCR-based assay for sensitive and specific detection of antibodies in serum or dried blood spots (DBS) is presented and the method is used to monitor individuals infected with or vaccinated against SARS-CoV-2. Detection probes were prepared by conjugating the recombinant spike protein subunit 1 (S1), containing the receptor binding domain (RBD) of SARS-CoV-2, to each of a pair of specific oligonucleotides. The same was done for the nucleocapsid protein (NP). Upon incubation with serum or DBS samples, the bi- or multivalency of the antibodies (IgG, IgA or IgM) brings pairs of viral proteins with their conjugated oligonucleotides in proximity, allowing the antibodies to be detected by a modified proximity extension assay (PEA). Anti-S1 and anti-NP antibodies could be detected simultaneously from one incubation reaction. This Antibody PEA (AbPEA) test uses only 1µl of neat or up to 100,000-fold diluted serum or one ø1.2mm disc cut from a DBS. All 100 investigated sera and 21 DBS collected prior to the COVID-19 outbreak were negative, demonstrating a 100% specificity. The area under the curve, as evaluated by Receiver Operating Characteristic (ROC) analysis reached 0.998 (95%CI: 0.993-1) for samples taken from 11 days after symptoms onset. The kinetics of antibody responses were monitored after a first and second vaccination using serially collected DBS from 14 individuals. AbPEA offers highly specific and sensitive solution-phase antibody detection without requirement for secondary antibodies, no elution step when using DBS sample in a simple procedure that lends itself to multiplex survey of antibody responses.
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