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Netrin (UNC-6) mediates dendritic self-avoidance

Abstract

Dendrites from a single neuron may be highly branched but typically do not overlap. Self-avoidance behavior has been shown to depend on cell-specific membrane proteins that trigger mutual repulsion. Here we report the unexpected discovery that a diffusible cue, the axon guidance protein UNC-6 (Netrin), is required for self-avoidance of sister dendrites from the PVD nociceptive neuron in Caenorhabditis elegans. We used time-lapse imaging to show that dendrites fail to withdraw upon mutual contact in the absence of UNC-6 signaling. We propose a model in which the UNC-40 (Deleted in Colorectal Cancer; DCC) receptor captures UNC-6 at the tips of growing dendrites for interaction with UNC-5 on the apposing branch to induce mutual repulsion. UNC-40 also responds to dendritic contact through another pathway that is independent of UNC-6. Our findings offer a new model for how an evolutionarily conserved morphogenic cue and its cognate receptors can pattern a fundamental feature of dendritic architecture.

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Figure 1: UNC-6 signaling is required for contact-dependent self-avoidance.
Figure 2: UNC-6 signaling is required for contact-dependent self-avoidance.
Figure 3: UNC-6 functions as a permissive cue to prevent dendritic branch overlap.
Figure 4: UNC-40 functions in PVD to mediate self-avoidance and captures exogenous UNC-6 at the PVD cell surface.
Figure 5: UNC-5 is required in PVD and uses UNC-40-independent signaling to mediate self-avoidance.

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Acknowledgements

We thank C. Bargmann (Rockefeller University) for unc-86UNC-40GFP, hsp16.2UNC-6HA and the CX6488 strain; W. Wadsworth (Rutgers University) for the pIM97 unc-6 expression construct and unc-6(rh46); K. Shen (Stanford University) for constructs used to make pCJS01, F49H12.4gatewaymcherry; P. Roy (University of Toronto) for the unc-40(e271) sequence; Y. Goshima (Yokohama City University) for ghIs9; J. Culotti (Mount Sinai Hospital, Toronto) for the unc-5 rescue construct and for the modified UNC-5 protein strains used for structure–function analysis and members of the D.M.M., R.B. and D.A.C.-R. laboratories for technical advice and for comments on the manuscript. Some of the strains used in this work were provided by the C. elegans Genetics Center, which is supported by the US National Institutes of Health (NIH) National Center for Research Resources. This work was supported by NIH R01 NS26115 (D.M.M.), NIH R21 NS06882 (D.M.M.), NIH F31 NS071801 (C.J.S.), NIH R00 NS057931 (D.A.C.-R.), the Klingenstein Foundation and an Alfred P. Sloan Foundation fellowship (D.A.C.-R.), and NIH MBRS SC3 GM089595 (M.K.V.).

Author information

Authors and Affiliations

Authors

Contributions

C.J.S. and D.M.M. designed the experiments. C.J.S. performed experiments with advice from D.M.M. J.D.W. helped with the phenotypic analysis of UNC-6 signaling mutants. D.A.C.-R. and M.K.V. provided reagents to test the cell-specific requirement of UNC-40 and UNC-6 and provided advice. C.J.S. and D.M.M. wrote the paper with input from coauthors.

Corresponding author

Correspondence to David M Miller III.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Text and Figures

Supplementary Figures 1–9, Supplementary Table 1 (PDF 870 kb)

Supplementary Movie 1

Wild-type self-avoidance. Time-lapse confocal movie of PVD::GFP in wild-type background. 3° dendrites contact but quickly retract (arrows). Note the intervening distance between 3O dendrites at the end of the movie is comparable to distance visualized in mature PVD neurons. Arrows indicate locations of contact-dependent self-avoidance. (MOV 8295 kb)

Supplementary Movie 2

Self-avoidance defect in unc-40(e271). Time-lapse confocal movie of PVD::GFP in unc-40(e271). 3° dendrites grow toward each other but upon contact fail to retract. Arrow indicates location of failed self-avoidance. (MOV 1892 kb)

Supplementary Movie 3

Self-avoidance defect in unc-5(e152). Imaging of unc-5(e152) shows PVD dendrites fail to retract after contact. Arrow indicates location of failed self-avoidance. (MOV 33275 kb)

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Smith, C., Watson, J., VanHoven, M. et al. Netrin (UNC-6) mediates dendritic self-avoidance. Nat Neurosci 15, 731–737 (2012). https://doi.org/10.1038/nn.3065

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