A synaptic laminin–calcium channel interaction organizes active zones in motor nerve terminals

Nishimune, Hiroshi; Sanes, Joshua R.; Carlson, Steven S.

doi:10.1038/nature03112

Cited by 249 publications

(392 citation statements)

References 38 publications

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“…Laminin-332 has an extremely important role in maintaining the structural integrity of the skin as evidenced by the fact that mutations in all three subunits of laminin-332 cause junctional epidermolysis bullosa, a severe, often lethal, inherited skin blistering disease 1,3 . Little is known about the effects of laminin isoforms on neuronal function, but β2-containing isoforms such as laminin-421 (previously laminin-9) participate in the organization of neuromuscular junction via β2-mediated interactions with the calcium channel Ca V 2.2 37 , and the same interaction has been proposed to be a stop signal for sensory axon growth in the skin 38 .…”

Section: Discussionmentioning

confidence: 99%

Laminin-332 coordinates mechanotransduction and growth cone bifurcation in sensory neurons

et al. 2011

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2 These authors made an equal contribution. Basement membrane molecules such as laminin are important structural components of the skin 1-4 , but also serve as substrates for sensory neurons of the dorsal root ganglia (DRG) to grow in culture 5 . The main function of sensory neurons innervating the skin is to detect and relay relevant sensory stimuli, in particular mechanical stimuli 6 . It has long been known that sensory neurons with a nociceptive function (detecting potentially harmful stimuli) can have their endings in the epidermis 7-9 whereas mechanoreceptor endings (touch receptors) reside exclusively in the dermal layer [9][10] . Interestingly, the matrix environments of the epidermis and the dermis are very distinctive 11 . We showed that mechanosensitive currents required for touch receptor function depend on the presence of a protein tether which may function to couple mechanosensitive channels to a laminin-containing matrix 12 . The tether protein is not required for the mechanosensitivity of most nociceptive sensory neurons. Here we set out to address the idea that sensory mechanotransduction might be modulated by distinct matrix components made by different types of skin cells in different skin layers. We show that epidermal keratinocytes produce a matrix that is non-permissive for mechanotransduction and identify the factor responsible as laminin-332 (formerly known as laminin-5). Laminin matrices doped with small amounts of laminin-332 have a dramatically altered network structure that is non-permissive for tether attachment.We demonstrate a spatially restricted loss of mechanotransduction in neurite segments connected to laminin-332-containing matrices. Mutations in all three genes coding the trimeric laminin-332 protein complex can cause epidermolysis bullosa, a severe inherited skin blistering disease 1,3 . Human keratinocytes that produce a laminin-332 free matrix have no inhibitory activity on mechanotransduction. We have also discovered an activity of laminin-332 matrix in inhibiting sensory axon bifurcation. Our results reveal novel mechanisms whereby permissive and non-permissive substrates can spatially coordinate mechanotransduction in distinct domains within a single neuron. Results Keratinocyte matrix is suppresses mechanotransductionUsing whole-cell, patch-clamp techniques we directly recorded mechanosensitive currents in cultured sensory neurons [12][13][14][15][16][17][18][19][20] . We first asked whether co-culture of sensory neurons with different cellular components of the skin can modulate the activity of mechanosensitive currents. When sensory neurons are cultured on a laminin substrate, standardly-derived from Engelbreth-Holm-Swarm cells (EHS matrix, henceforth referred to as laminin), more than 90% of the cells exhibit a mechanosensitive current evoked using a small (~740 nm displacement) stimulus to the neurite 12, 14-15 . At least three types of mechanosensitive current can be measured in sensory neurons, classified according to their inactivation time constant τ 1 , rap...

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Section: Discussionmentioning

confidence: 99%

Laminin-332 coordinates mechanotransduction and growth cone bifurcation in sensory neurons

et al. 2011

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“…Therefore, agrin may evoke signals other than MuSK activation by binding to laminins and/or Lrp4. Because the laminin β2-subunit acts as an essential presynaptic organizer after, but not before, birth by binding to the presynaptic voltage-gated calcium channels at NMJs (33)(34)(35), agrin might promote the presynaptic specialization essential for NMJ maintenance via interaction with the laminins containing the β2-subunit. Notably, this hypothetical role for agrin could explain our finding that agrin deficiency impaired motor innervation as judged by the coverage of presynaptic nerve terminals over postsynaptic AChR clusters (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Given that the exogenous Dok-7-mediated MuSK activation was maintained at a high level ( Only a few elements that play indispensable roles in the postnatal maintenance, but not prenatal formation, of NMJs have been suggested (32). The laminin β2-subunit is one such element; mice lacking it show no defects in NMJ formation during embryogenesis and the first few postnatal days, but develop presynaptic defects by 1 wk after birth, leading to lethality during the third postnatal week (33)(34)(35). Interestingly, agrin-deficient mice are rescued by muscle-specific expression of "mini-agrin," which retains only agrin's laminin-binding and MuSK-activating (Lrp4-binding) regions (36).…”

Section: Discussionmentioning

confidence: 99%

The MuSK activator agrin has a separate role essential for postnatal maintenance of neuromuscular synapses

Tezuka

Inoue

Hoshi

et al. 2014

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

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The motoneural control of skeletal muscle contraction requires the neuromuscular junction (NMJ), a midmuscle synapse between the motor nerve and myotube. The formation and maintenance of NMJs are orchestrated by the muscle-specific receptor tyrosine kinase (MuSK). Motor neuron-derived agrin activates MuSK via binding to MuSK's coreceptor Lrp4, and genetic defects in agrin underlie a congenital myasthenic syndrome (an NMJ disorder). However, MuSK-dependent postsynaptic differentiation of NMJs occurs in the absence of a motor neuron, indicating a need for nerve/agrin-independent MuSK activation. We previously identified the muscle protein Dok-7 as an essential activator of MuSK. Although NMJ formation requires agrin under physiological conditions, it is dispensable for NMJ formation experimentally in the absence of the neurotransmitter acetylcholine, which inhibits postsynaptic specialization. Thus, it was hypothesized that MuSK needs agrin together with Lrp4 and Dok-7 to achieve sufficient activation to surmount inhibition by acetylcholine. Here, we show that forced expression of Dok-7 in muscle enhanced MuSK activation in mice lacking agrin or Lrp4 and restored midmuscle NMJ formation in agrin-deficient mice, but not in Lrp4-deficient mice, probably due to the loss of Lrp4-dependent presynaptic differentiation. However, these NMJs in agrin-deficient mice rapidly disappeared after birth, and postsynaptic specializations emerged ectopically throughout myotubes whereas exogenous Dok-7-mediated MuSK activation was maintained. These findings demonstrate that the MuSK activator agrin plays another role essential for the postnatal maintenance, but not for embryonic formation, of NMJs and also for the postnatal, but not prenatal, midmuscle localization of postsynaptic specializations, providing physiological and pathophysiological insight into NMJ homeostasis. neuromuscular junction | postsynaptic specialization | Dok-7 | Lrp4

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“…Nevertheless, for each junction imaged and immunostained there was a high correlation coefficient between ⌬F stim and SV2 labeling, further emphasizing the connection between evoked synaptic vesicle release and vesicle pool size. It will be of interest to know whether the distribution of other proteins, such as those in active zones (Nishimune et al, 2004;Juranek et al, 2006) is also correlated to the relative amount of synaptic vesicle release across regions of a terminal.…”

Section: Discussionmentioning

confidence: 99%

Heterogeneity in Synaptic Vesicle Release at Neuromuscular Synapses of Mice Expressing SynaptopHluorin

Wyatt

Balice-Gordon²

2008

J. Neurosci.

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Mammalian neuromuscular junctions are useful model synapses to study the relationship between synaptic structure and function, although these have rarely been studied together at the same synapses. To do this, we generated transgenic lines of mice in which the thy1.2 promoter drives expression of synaptopHluorin (spH) as a means of optically measuring synaptic vesicle distribution and release. SpH is colocalized with other synaptic vesicle proteins in presynaptic terminals and does not alter normal synaptic function. Nerve stimulation leads to readily detectable and reproducible fluorescence changes in motor axon terminals that vary with stimulus frequency and, when compared with electrophysiological recordings, are reliable indicators of neurotransmitter release. Measurements of fluorescence intensity changes reveal a surprising amount of heterogeneity in synaptic vesicle release throughout individual presynaptic motor axon terminals. Some discrete terminal regions consistently displayed a greater rate and extent of release than others, regardless of stimulation frequency. The amount of release at a particular site is highly correlated to the relative abundance of synaptic vesicles there, indicating that a relatively constant fraction of the total vesicular pool, ϳ30%, is released in response to activity. These studies reveal previously unknown relationships between synaptic structure and function at mammalian neuromuscular junctions and demonstrate the usefulness of spH expressing mice as a tool for studying neuromuscular synapses in adults, as well as during development and diseases that affect neuromuscular synaptic function.

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A synaptic laminin–calcium channel interaction organizes active zones in motor nerve terminals

Cited by 249 publications

References 38 publications

Laminin-332 coordinates mechanotransduction and growth cone bifurcation in sensory neurons

Laminin-332 coordinates mechanotransduction and growth cone bifurcation in sensory neurons

The MuSK activator agrin has a separate role essential for postnatal maintenance of neuromuscular synapses

Heterogeneity in Synaptic Vesicle Release at Neuromuscular Synapses of Mice Expressing SynaptopHluorin

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