Neuromuscular synaptogenesis in wild-type and mutant zebrafish

Department of Neuroscience, University of Pennsylvania School of Medicine, 215 Stemmler Hall, 3610 Hamilton Walk, Philadelphia, PA 19104-6074, USA.
Developmental Biology (Impact Factor: 3.64). 10/2005; 285(2):340-57. DOI: 10.1016/j.ydbio.2005.06.027
Source: PubMed

ABSTRACT Genetic screens for synaptogenesis mutants have been performed in many organisms, but few if any have simultaneously screened for defects in pre- and postsynaptic specializations. Here, we report the results of a small-scale genetic screen, the first in vertebrates, for defects in synaptogenesis. Using zebrafish as a model system, we identified seven mutants that affect different aspects of neuromuscular synapse formation. Many of these mutant phenotypes have not been previously reported in zebrafish and are distinct from those described in other organisms. Characterization of mutant and wild-type zebrafish, from the time that motor axons first arrive at target muscles through adulthood, has provided the new information about the cellular events that occur during neuromuscular synaptogenesis. These include insights into the formation and dispersal of prepatterned AChR clusters, the relationship between motor axon elongation and synapse size, and the development of precise appositions between presynaptic clusters of synaptic vesicles in nerve terminals and postsynaptic receptor clusters. In addition, we show that the mechanisms underlying synapse formation within the myotomal muscle itself are largely independent of those that underlie synapse formation at myotendinous junctions and that the outgrowth of secondary motor axons requires at least one cue not necessary for the outgrowth of primary motor axons, while other cues are required for both. One-third of the mutants identified in this screen did not have impaired motility, suggesting that many genes involved in neuromuscular synaptogenesis were missed in large scale motility-based screens. Identification of the underlying genetic defects in these mutants will extend our understanding of the cellular and molecular mechanisms that underlie the formation and function of neuromuscular and other synapses.

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Available from: Roland Dosch, Jul 07, 2015
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    • "Thus, the NMJ is an attractive model for studying the sequence of events during synapse assembly. Furthermore, because myotubes and motor neurons develop in a rostral-to-caudal progression, the whole sequence of events underlying NMJ assembly can be viewed in a single zebrafish embryo (Flanagan-Steet et al., 2005; Panzer et al., 2005, 2006). Two time lapse imaging studies have demonstrated that prepatterned AChRs exist on muscle fibers before the arrival of motor axons (Flanagan-Steet et al., 2005; Panzer et al., 2006). "
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    • "Immunostaining of embryos at various developmental stages was performed as previously described (Panzer et al., 2005). F59 (monoclonal anti-slow myosin heavy chain, Developmental Studies Hybridoma Bank (DSHB) (Miller et al., 1985)) was used at 1:20 dilution (Devoto et al., 1996), Alexa Fluor 488 conjugated α-bungarotoxin (Invitrogen) was used at 10 μg/ml following manufacturer's instructions, SV2 (monoclonal anti-synaptic vesicles, DSHB (Buckley and Kelly, 1985)) secondarily bound to Alexa Fluor 546 conjugated antibody (Molecular Probes) was used at 1:100 dilution, and Alexa Fluor 488 conjugated phalloidin (Invitrogen) was used at 1 unit/ml following manufacturer's instructions. "
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    • "At 24 hpf, from 187 normally developed embryos, 173 (93%) of the embryos contained EGFP expressing cells. Embryos were fixed, immunostained with SV2 and znp1 antibodies to label axons and nerve terminals (Brusés, in press; Panzer et al., 2005), and observed by confocal microscopy to determine the pattern of EGFP expression (see Fig 1). At 24 hpf, EGFP was detected in a few primary motor neurons with an average of 11.4 neurons per embryo (Table 2). "
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