From Plaque To Pretzel: Fold Formation And Acetylcholine Receptor Loss At The Developing Neuromuscular Junction

Although there has been progress in understanding the initial steps in the formation of synapses, less is known about their subsequent maturation (Sanes and Lichtman, 1999). Two alterations on the postsynaptic side of the mammalian neuromuscular junction occur during early postnatal life: acetylcholine receptors (AChRs) disappear from parts of the developing junction as all but one axonal inputs are removed, and the topography of the postsynaptic membrane becomes more complicated as gutters and folds are established. We have studied the maturation of the AChR distribution and postsynaptic topography simultaneously by imaging labeled AChRs at the mouse neuromuscular junction in a new way, using reflected light confocal microscopy. At birth postsynaptic receptors were localized in irregular patches within a spoon-shaped plaque. Beginning several days later, receptor regions within a single endplate were divided into differentiated and less organized compartments. Folds generally oriented orthogonal to the long axis of the muscle fiber were seen in developing gutters, although the orientation of the gutters seemed to be imposed by the branching pattern of the nerve. Eventually, superficial regions lacking AChR labeling were apparent in all junctions. In junctions denervated in the neonatal period both gutter formation and the disappearance of superficial receptors regions were prevented. We suggest that tension between growing muscle fibers and the relatively inelastic synaptic terminals that adhere to them causes the topographic features of the postsynaptic membrane. 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Rapid Synapse Elimination After Postsynaptic Protein Synthesis Inhibition In Vivo

To examine the role of retrograde signals on synaptic maintenance, we inhibited protein synthesis in individual postsynaptic cells in vivo while monitoring presynaptic terminals. Within 12 h, axon terminals begin to atrophy and withdraw from normal postsynaptic sites. Structural similarities between this process and naturally occurring synapse elimination suggest that short-lived target derived factors not only participate in synaptic maintenance in adults, but also regulate elimination of connections during development. Copyright © 2007 Society for Neuroscience.272260646067Bishop, D.L., Misgeld, T., Walsh, M.K., Gan, W.B., Lichtman, J.W., Axon branch removal at developing synapses by axosome shedding (2004) Neuron, 44, pp. 651-661Culican, S.M., Nelson, C.C., Lichtman, J.W., Axon withdrawal during synapse elimination at the neuromuscular junction is accompanied by disassembly of the postsynaptic specialization and withdrawal of Schwann cell processes (1998) J Neurosci, 18, pp. 4953-4965Feng, G., Mellor, R.H., Bernstein, M., Keller-Peck, C., Nguyen, Q.T., Wallace, M., Nerbonne, J.M., Sanes, J.R., Imaging neuronal subsets in transgenic mice expressing multiple spectral variants of GFP (2000) Neuron, 28, pp. 41-51Gan, W.B., Lichtman, J.W., Synaptic segregation at the developing neuromuscular junction (1998) Science, 282, pp. 1508-1511Keller-Peck, C.R., Walsh, M.K., Gan, W.B., Feng, G., Sanes, J.R., Lichtman, J.W., Asynchronous synapse elimination in neonatal motor units: Studies using GFP transgenic mice (2001) Neuron, 31, pp. 381-394Kerschensteiner, M., Schwab, M.E., Lichtman, J.W., Misgeld, T., In vivo imaging of axonal degeneration and regeneration in the injured spinal cord (2005) Nat Med, 11, pp. 572-577Kishida, K., Masuho, Y., Hara, T., Protein-synthesis inhibitory protein from seeds of Luffa cylindria roem (1983) FEBS Letters, 153, pp. 209-212Lichtman, J.W., Magrassi, L., Purves, D., Visualization of neuromuscular junctions over periods of several months in living mice (1987) J Neurosci, 7, pp. 1215-1222Nguyen, Q.T., Parsadanian, A.S., Snider, W.D., Lichtman, J.W., Hyperinnervation of neuromuscular junctions caused by GDNF overexpression in muscle (1998) Science, 279, pp. 1725-1729Portera-Cailliau, C., Weimer, R.M., De Paola, V., Caroni, P., Svoboda, K., Diverse modes of axon elaboration in the developing neocortex (2005) PLoS Biol, 3, pp. e272Reynolds, M.L., Woolf, C.J., Terminal Schwann cells elaborate extensive processes following denervation of the motor endplate (1992) J Neurocytol, 21, pp. 50-66Sanes, J.R., Lichtman, J.W., Induction, assembly, maturation and maintenance of a postsynaptic apparatus (2001) Nat Rev Neurosci, 2, pp. 791-805Sigrist, S.J., Thiel, P.R., Reiff, D.F., Lachance, P.E., Lasko, P., Schuster, C.M., Postsynaptic translation affects the efficacy and morphology of neuromuscular junctions (2000) Nature, 405, pp. 1062-1065Stirpe F, Gasperi-Campani A, Barbieri L, Falasca A, Abbondanza A, Stevens WA (1983) Ribosome-inactivating proteins from the seeds of Saponaria officinalis L. (soapwort), of Agrostemma githago L. (corn cockle) and of Asparagus officinalis L. (asparagus), and from the latex of Hura crepitans L. (sandbox tree). Biochem J 216:617-625Stirpe, F., Barbieri, L., Battelli, M.G., Soria, M., Lappi, D.A., Ribosome-inactivating proteins from plants: Present status and future prospects (1992) Biotechnology (NY), 10, pp. 405-412Tao, H.W., Poo, M., Retrograde signaling at central synapses (2001) Proc Natl Acad Sci USA, 98, pp. 11009-11015Walsh, M.K., Lichtman, J.W., In vivo time-lapse imaging of synaptic takeover associated with naturally occurring synapse elimination (2003) Neuron, 37, pp. 67-73Watts, R.J., Schuldiner, O., Perrino, J., Larsen, C., Luo, L., Glia engulf degenerating axons during developmental axon pruning (2004) Curr Biol, 14, pp. 678-684Zuo, Y., Lubischer, J.L., Kang, H., Tian, L., Mikesh, M., Marks, A., Scofield, V.L., Thompson, W.J., Fluorescent proteins expressed in mouse transgenic lines mark subsets of glia, neurons, macrophages, and dendritic cells for vital examination (2004) J Neurosci, 24, pp. 10999-1100

Comment on "Reelin promotes peripheral synapse elimination and maturation".

Comment on: Science. 2003 Aug 1;301(5633):649-5