Glycoproteins of the Synaptic Region

1986 ◽

Vol 44 ◽

pp. 278-279

Author(s):

W. L. Steffens ◽

Nancy B. Roberts ◽

J. M. Bowen

Keyword(s):

Dirofilaria Immitis ◽

Domestic Dogs ◽

Structural Description ◽

Pharmacological Effects ◽

Free Living ◽

Canine Heartworm ◽

The World ◽

Synaptic Region ◽

Muscle Innervation ◽

Insight Into

The canine heartworm is a common and serious nematode parasite of domestic dogs in many parts of the world. Although nematode neuroanatomy is fairly well documented, the emphasis has been on sensory anatomy and primarily in free-living soil species and ascarids. Lee and Miller reported on the muscular anatomy in the heartworm, but provided little insight into the peripheral nervous system or myoneural relationships. The classical fine-structural description of nematode muscle innervation is Rosenbluth's earlier work in Ascaris. Since the pharmacological effects of some nematacides currently being developed are neuromuscular in nature, a better understanding of heartworm myoneural anatomy, particularly in reference to the synaptic region is warranted.

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Synapsin I (protein I), a nerve terminal-specific phosphoprotein. I. Its general distribution in synapses of the central and peripheral nervous system demonstrated by immunofluorescence in frozen and plastic sections.

The Journal of Cell Biology ◽

10.1083/jcb.96.5.1337 ◽

1983 ◽

Vol 96 (5) ◽

pp. 1337-1354 ◽

Cited By ~ 345

Author(s):

P De Camilli ◽

R Cameron ◽

P Greengard

Keyword(s):

Nervous System ◽

Detailed Examination ◽

Specific Protein ◽

Nerve Cells ◽

General Distribution ◽

Synapsin I ◽

Nervous Systems ◽

Synaptic Region ◽

Specific Localization ◽

Peripheral Nervous Systems

Synapsin I (formerly referred to as protein I) is the collective name for two almost identical phosphoproteins, synapsin Ia and synapsin Ib (protein Ia and protein Ib), present in the nervous system. Synapsin I has previously been shown by immunoperoxidase studies (De Camilli, P., T. Ueda, F. E. Bloom, E. Battenberg, and P. Greengard, 1979, Proc. Natl. Acad. Sci. USA, 76:5977-5981; Bloom, F. E., T. Ueda, E. Battenberg, and P. Greengard, 1979, Proc. Natl. Acad. Sci. USA 76:5982-5986) to be a neuron-specific protein, present in both the central and peripheral nervous systems and concentrated in the synaptic region of nerve cells. In those preliminary studies, the occurrence of synapsin I could be demonstrated in only a portion of synapses. We have now carried out a detailed examination of the distribution of synapsin I immunoreactivity in the central and peripheral nervous systems. In this study we have attempted to maximize the level of resolution of immunohistochemical light microscopy images in order to estimate the proportion of immunoreactive synapses and to establish their precise distribution. Optimal results were obtained by the use of immunofluorescence in semithin sections (approximately 1 micron) prepared from Epon-embedded nonosmicated tissues after the Epon had been removed. Our results confirm the previous observations on the specific localization of synapsin I in nerve cells and synapses. In addition, the results strongly suggest that, with a few possible exceptions involving highly specialized neurons, all synapses contain synapsin I. Finally, immunocytochemical experiments indicate that synapsin I appearance in the various regions of the developing nervous system correlates topographically and temporally with the appearance of synapses. In two accompanying papers (De Camilli, P., S. M. Harris, Jr., W. B. Huttner, and P. Greengard, and Huttner, W. B., W. Schiebler, P. Greengard, and P. De Camilli, 1983, J. Cell Biol. 96:1355-1373 and 1374-1388, respectively), evidence is presented that synapsin I is specifically associated with synaptic vesicles in nerve endings.

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GA-Binding Protein Is Dispensable for Neuromuscular Synapse Formation and Synapse-Specific Gene Expression

Molecular and Cellular Biology ◽

10.1128/mcb.02228-06 ◽

2007 ◽

Vol 27 (13) ◽

pp. 5040-5046 ◽

Cited By ~ 22

Author(s):

Alexander Jaworski ◽

Cynthia L. Smith ◽

Steven J. Burden

Keyword(s):

Gene Expression ◽

Synapse Formation ◽

Binding Protein ◽

Neuromuscular Synapse ◽

Specific Gene ◽

Promoter Regions ◽

Specific Gene Expression ◽

Muscle Gene Expression ◽

Synaptic Region ◽

Ga Binding Protein

ABSTRACT The mRNAs encoding postsynaptic components at the neuromuscular junction are concentrated in the synaptic region of muscle fibers. Accumulation of these RNAs in the synaptic region is mediated, at least in part, by selective transcription of the corresponding genes in synaptic myofiber nuclei. The transcriptional mechanisms that are responsible for synapse-specific gene expression are largely unknown, but an Ets site in the promoter regions of acetylcholine receptor (AChR) subunit genes and other “synaptic” genes is required for synapse-specific transcription. The Ets domain transcription factor GA-binding protein (GABP) has been implicated to mediate synapse-specific gene expression. Inactivation of GABPα, the DNA-binding subunit of GABP, leads to early embryonic lethality, preventing analysis of synapse formation in gabpα mutant mice. To study the role of GABP at neuromuscular synapses, we conditionally inactivated gabpα in skeletal muscle and studied synaptic differentiation and muscle gene expression. Although expression of rb, a target of GABP, is elevated in muscle tissue deficient in GABPα, clustering of synaptic AChRs at synapses and synapse-specific gene expression are normal in these mice. These data indicate that GABP is dispensable for synapse-specific transcription and maintenance of normal AChR expression at synapses.

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Synaptic basal lamina contains a signal for synapse-specific transcription

Development ◽

10.1242/dev.115.3.673 ◽

1992 ◽

Vol 115 (3) ◽

pp. 673-680 ◽

Cited By ~ 1

Author(s):

S.A. Jo ◽

S.J. Burden

Keyword(s):

Acetylcholine Receptor ◽

Basal Lamina ◽

Motor Nerve ◽

Receptor Gene ◽

High Rate ◽

Denervated Muscle ◽

Transcriptional Pattern ◽

Synaptic Region ◽

Acetylcholine Receptor Gene ◽

Continuous Presence

Nuclei in the synaptic region of multinucleated skeletal myofibers are transcriptionally distinct, since acetylcholine receptor genes are transcribed at a high rate by these nuclei, but not by nuclei elsewhere in the myofiber. Although this spatially restricted transcription pattern is presumably imposed by the motor nerve, the continuous presence of the nerve is not required, since synapse-specific transcription persists after denervation. These results suggest either that a transcriptional signal persists at synaptic sites after nerve terminals have degenerated, or that a transcriptional pattern in the myofiber, once established, is stable in the absence of a nerve-derived signal. To distinguish between these possibilities, we denervated muscle and damaged the myofibers and specialized cells located near synaptic sites, and then studied transcription of an acetylcholine receptor gene in myofibers that regenerated in their original basal lamina sheaths, but remained denervated. We show that synapse-specific transcription is re-induced in these regenerated myofibers, and we conclude that a signal for synapse-specific transcription is stably maintained in the synaptic basal lamina.

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Rapid dispersal of clustered postsynaptic nuclei following dissociation of skeletal muscle fibers.

Journal of Experimental Biology ◽

10.1242/jeb.199.11.2359 ◽

1996 ◽

Vol 199 (11) ◽

pp. 2359-2367

Author(s):

C Brösamle ◽

D P Kuffler

Keyword(s):

Skeletal Muscle ◽

Synapse Formation ◽

Contractile Activity ◽

Muscle Fibers ◽

Skeletal Muscle Fibers ◽

Synaptic Region ◽

Nuclear Clusters ◽

Specialized Structure

The vertebrate neuromuscular junction is a highly specialized structure containing many unique proteins and an underlying cluster of nuclei. Part of this specialization results from the expression of the genes for these proteins in nuclei clustered in the postsynaptic region. Contractile activity, as well as molecules located in the synaptic extracellular matrix (ECM), have been implicated in the induction of gene expression in these clustered nuclei. The present experiments were aimed at examining whether the presence of the synaptic ECM and presynaptic cells play a role in maintaining the clustering of the nuclei. We describe the normal distribution of nuclei clustered in the synaptic region of intact adult frog, Rana pipiens, skeletal muscle fibers and show that innervation is not required to maintain the nuclear clusters. Even after long-term (4 week) denervation, the clusters remain unchanged. Dissociation of the muscle fibers with proteases that remove ECM, Schwann cells and other satellite cells from the synaptic sites is followed by a rapid (within approximately 1.5 h) and almost complete dispersal of the clustered nuclei. Attempts to recluster the postsynaptic nuclei by the application of ECM components to muscle fibers in vitro were not successful. We propose that a factor or factors, localized in the synaptic ECM as a result of synapse formation and acting via the transmembrane or cytoplasmic domains of their respective receptors, induces the formation of a specialized cytoskeleton in the postsynaptic region that is capable of pulling in or 'trapping' nuclei. The removal of these factors from the ECM by proteases brings about the disorganization of the cytoskeleton and the freeing of the 'trapped' nuclei.

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