A stoichiometric complex of neurexins and dystroglycan in brain

Neurexins are evolutionarily conserved presynaptic cell-adhesion molecules that are essential for normal synapse formation and synaptic transmission. Indirect evidence has indicated that extensive alternative splicing of neurexin mRNAs may produce hundreds if not thousands of neurexin isoforms, but no direct evidence for such diversity has been available. Here we use unbiased long-read sequencing of full-length neurexin (Nrxn)1α, Nrxn1β, Nrxn2β, Nrxn3α, and Nrxn3β mRNAs to systematically assess how many sites of alternative splicing are used in neurexins with a significant frequency, and whether alternative splicing events at these sites are independent of each other. In sequencing more than 25,000 full-length mRNAs, we identified a novel, abundantly used alternatively spliced exon of Nrxn1α and Nrxn3α (referred to as alternatively spliced sequence 6) that encodes a 9-residue insertion in the flexible hinge region between the fifth LNS (laminin-α, neurexin, sex hormone-binding globulin) domain and the third EGF-like sequence. In addition, we observed several larger-scale events of alternative splicing that deleted multiple domains and were much less frequent than the canonical six sites of alternative splicing in neurexins. All of the six canonical events of alternative splicing appear to be independent of each other, suggesting that neurexins may exhibit an even larger isoform diversity than previously envisioned and comprise thousands of variants. Our data are consistent with the notion that α-neurexins represent extracellular protein-interaction scaffolds in which different LNS and EGF domains mediate distinct interactions that affect diverse functions and are independently regulated by independent events of alternative splicing.N eurons form highly specific and complex patterns of synaptic connections that underlie all brain function (1-5). Such specific connections require trillions of chemically differentiated synapses whose identity may be shaped by interactions of specific pre-and postsynaptic signaling molecules, especially cell-adhesion molecules. The genome size is insufficient to encode such diversity, but a mixture of combinatorial expression patterns that pair different synaptic cell-adhesion molecules with each other and of distinct alternative splicing patterns that amplify the number of cell-adhesion molecules into a large number of isoforms may generate the number of transsynaptic interactions needed to account for the enormous diversity of synaptic connections. In Drosophila melanogaster, alternative splicing of the mRNAs encoding the Down syndrome cell-adhesion molecule can generate nearly 20,000 protein isoforms whose structures specify axon bundling but not synapse formation (6). In mammals, alternative splicing of neurexin and some protocadherin mRNAs can also produce thousands of isoforms, which may at least in the case of neurexins be involved in synapse formation (7-10).Neurexins are type I membrane proteins that were discovered as presynaptic receptors for α-latrotoxin (8, 9). Six prin...

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“…In addition to these ligands, neurexins were shown to bind to neurexophilin, dystroglycan, and CIRL/ latrophilin (32)(33)(34)(35).…”

Section: Significancementioning

confidence: 99%

Cartography of neurexin alternative splicing mapped by single-molecule long-read mRNA sequencing

Treutlein¹,

Gökçe

Quake

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

296

262

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“…Interaction between α-dystroglycan and α-/β-neurexins by means of laminin-neurexin-sex hormone-binding globulin (LNS)/laminin G domains has been reported several years ago [101], and was proposed to compete with α-latrotoxin binding on neurexins. In addition, binding of synaptic scaffolding molecule (S-SCAM) to β-dystroglycan and NL2 has been characterized in studies showing the selective presence of S-SCAM at inhibitory synaptic sites [102,103].…”

Section: The Dystrophin-glycoprotein Complexmentioning

confidence: 99%

Molecular and functional heterogeneity of GABAergic synapses

Fritschy

Panzanelli

Tyagarajan

2012

Cell. Mol. Life Sci.

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Knowledge of the functional organization of the GABAergic system, the main inhibitory neurotransmitter system, in the CNS has increased remarkably in recent years. In particular, substantial progress has been made in elucidating the molecular mechanisms underlying the formation and plasticity of GABAergic synapses. Evidence available ascribes a key role to the cytoplasmic protein gephyrin to form a postsynaptic scaffold anchoring GABA(A) receptors along with other transmembrane proteins and signaling molecules in the postsynaptic density. However, the mechanisms of gephyrin scaffolding remain elusive, notably because gephyrin can auto-aggregate spontaneously and lacks PDZ protein interaction domains found in a majority of scaffolding proteins. In addition, the structural diversity of GABA(A) receptors, which are pentameric channels encoded by a large family of subunits, has been largely overlooked in these studies. Finally, the role of the dystrophin-glycoprotein complex, present in a subset of GABAergic synapses in cortical structures, remains ill-defined. In this review, we discuss recent results derived mainly from the analysis of mutant mice lacking a specific GABA(A) receptor subtype or a core protein of the GABAergic postsynaptic density (neuroligin-2, collybistin), highlighting the molecular diversity of GABAergic synapses and its relevance for brain plasticity and function. In addition, we discuss the contribution of the dystrophin-glycoprotein complex to the molecular and functional heterogeneity of GABAergic synapses. AbstractKnowledge of the functional organization of the GABAergic system, the main inhibitory neurotransmitter system, in the CNS has increased remarkably in recent years. In particular, substantial progress has been made in elucidating the molecular mechanisms underlying formation and plasticity of GABAergic synapses. Evidence available ascribes a key role to the cytoplasmic protein gephyrin to form a postsynaptic scaffold anchoring GABA A receptors along with other transmembrane proteins and signaling molecules in the postsynaptic density. However, the mechanisms of gephyrin scaffolding remain elusive, notably because gephyrin can auto-aggregate spontaneously and lacks PDZ protein interaction domains found in a majority of scaffolding proteins. In addition, the structural diversity of GABA A receptors, which are pentameric channels encoded by a large family of subunits, has been largely overlooked in these studies. Finally, the role of the dystrophin-glycoprotein complex, present in a subset of GABAergic synapses in cortical structures, remains ill-defined. In this review, we discuss recent results derived mainly from the analysis of mutant mice lacking a specific GABA A receptor subtype or a core protein of the GABAergic postsynaptic density (neuroligin-2, collybistin), highlighting the molecular diversity of GABAergic synapses and its relevance for brain plasticity and function. In addition, we discuss the contribution of the dystrophinglycoprotein complex to the molecular ...

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“…The parenchymal basement membrane contains laminins, α1 and α2, compared with the endothelial basal lamina that only contains laminin α4 [49,57] suggesting a more complex barrier. Additionally, the parenchymal basement membrane is linked to the astrocytic endfoot membrane through interactions with ECM components present on both sides [51,52]. Dystroglycan, which is exclusively expressed on the astrocytic endfoot membrane [53,64] participates in these interactions, and it is known to be a substrate of MMP-2 and -9 [1].…”

Section: Discussionmentioning

confidence: 99%

Multiple expression of matrix metalloproteinases in murine neurocysticercosis: Implications for leukocyte migration through multiple central nervous system barriers

Alvarez

Teale

2008

Brain Research

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During the course of murine neurocysticercosis (NCC), disruption of the unique protective barriers in the central nervous system (CNS) is evidenced by extravasation of leukocytes. This process varies according to the anatomical sites and diverse vascular beds analyzed. To examine mechanisms involved in the observed differences, the expression and activity of eight matrix metalloproteinases (MMPs) were analyzed in a murine model of NCC. The mRNA expression of the MMPs studied was upregulated as a result of infection, and active MMPs were mainly detected in leukocytes migrating into the brain. Polarized expression and gelatinolytic activity of several MMPs were identified in immune cells extravasating pial vessels as early as 1 day post infection. In contrast, leukocytes expressing active MMPs and extravasating parenchymal vessels were not observed until 5 weeks post infection. In ventricular areas, most of the MMP activity was detected in leukocytes traversing the ependyma from leptomeningeal infiltrates. In addition, immune cells continued to express active MMPs after exiting vessels suggesting that enzymatic activity of MMPs is not just required for diapedesis. These results correlate with our previous studies showing differential kinetics in the disruption of the CNS barriers upon infection and help document the important role of MMPs during leukocyte infiltration and inflammation.

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A stoichiometric complex of neurexins and dystroglycan in brain

Cited by 400 publications

References 62 publications

Cartography of neurexin alternative splicing mapped by single-molecule long-read mRNA sequencing

Cartography of neurexin alternative splicing mapped by single-molecule long-read mRNA sequencing

Molecular and functional heterogeneity of GABAergic synapses

Multiple expression of matrix metalloproteinases in murine neurocysticercosis: Implications for leukocyte migration through multiple central nervous system barriers

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