Abstract
Axons are defined by the presence of presynaptic specializations at specific locations. We show here that loss-of-function mutations in the C. elegans gene syd-1 cause presynaptic specializations to form in the dendritic processes of GABA-expressing motor neurons during initial differentiation. At a later developmental stage, however, syd-1 is not required for the polarity respecification of a subset of these neurons. The SYD-1 protein contains PDZ, C2 and rho–GTPase activating protein (GAP)-like domains, and is localized to presynaptic terminals in mature neurons. A truncated SYD-1 that lacks the rhoGAP domain interferes with neurite outgrowth and guidance. Our data indicate that syd-1 may be involved in specifying axon identity during initial polarity acquisition.
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Acknowledgements
We thank M. Nonet, C. Bargmann, J. Kaplan, B. Herman, B. Bamber, Y. Kohara, A. Coulson and the C. elegans genome consortium for reagents; W. Harris and K. Guan for biochemistry of SYD-1 GAP; B. Ackley, C. Suh, K. Hudson, K. Hoogner, M. Verado and M. Crookham for assistance; A. Chisholm, M. Zhen and our lab members for discussions and comments. We obtained some of these strains from the Caenorhabditis Genetics Center, which is supported by a grant from the National Institutes of Health. This work was funded by a National Science Foundation Presidential Early Career award (Y.J.) and an NSF equipment grant DBI-9729596. S.H. was supported by a GAANN predoctoral fellowship; R.B. was supported by a National Research Service Award postdoctoral fellowship. A.G. is an HHMI research associate, and Y.J. is an assistant investigator of HHMI.
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Supplementary Fig. 1.
Effect of syd-1 on neuronal morphology, dendro-soma markers and ASI neuron polarity. (a, b) The overall axon morphology and cell body positions of DD and VD motor neurons in wild-type (a) and syd-1 mutant (b). No differences seen. (c, d) The expression of OSM-6::GFP (mnIs17) in phasmid neurons in wild type (c) and syd-1 mutants (d) is the same. Arrowhead, cell bodies; thin arrows, dendrites. (e, f) The expression of GLR-1::GFP (nuIs25) in the ventral cord (arrows) is the same in wild-type (e) and syd-1 mutants (f). (g) In wild-type animals, ASI neurons project a single anterior directed dendrite and a single axonal process fasiculated in the nerve ring, and the expression of SNB::GFP is restricted to the axonal projection (arrow), as illustrated in (i). (h) In syd-1 mutants, fewer SNB::GFP puncta in the axonal region of ASI (arrow) are present and irregular in size, and also mis-localized to the dendritic region (arrowhead), as illustrated in (j). * indicates posteriorly wandered axon. (JPG 41 kb)
Supplementary Fig. 2.
Sequence alignment of PDZ and C2 domains. (a) Alignment of the PDZ domain (residue 55-142). * indicates residues of PDZ-3 of PSD-95 that are required for substrate binding. (b) Alignment of the C2 domain (residue 548-671). * marks the W598A mutation. (GIF 33 kb)
Supplementary Table 1.
Quantitation of cell autonomy for SYD-1 and the effect of mutations in the C2 and GAP domains. Multiple independent transgenic lines for each construct were inspected. Quantitations were made on the staged worms from the most representative lines. (GIF 30 kb)
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Hallam, S., Goncharov, A., McEwen, J. et al. SYD-1, a presynaptic protein with PDZ, C2 and rhoGAP-like domains, specifies axon identity in C. elegans. Nat Neurosci 5, 1137–1146 (2002). https://doi.org/10.1038/nn959
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DOI: https://doi.org/10.1038/nn959
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