Article

Glia initiate brain assembly through noncanonical Chimaerin–Furin axon guidance in C. elegans

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Abstract

Brain assembly is hypothesized to begin when pioneer axons extend over non-neuronal cells, forming tracts guiding follower axons. Yet pioneer-neuron identities, their guidance substrates, and their interactions are not well understood. Here, using time-lapse embryonic imaging, genetics, protein-interaction, and functional studies, we uncover the early events of C. elegans brain assembly. We demonstrate that C. elegans glia are key for assembly initiation, guiding pioneer and follower axons using distinct signals. Pioneer sublateral neurons, with unique growth properties, anatomy, and innervation, cooperate with glia to mediate follower-axon guidance. We further identify a Chimaerin (CHIN-1)– Furin (KPC-1) double-mutant that severely disrupts assembly. CHIN-1 and KPC-1 function noncanonically, in glia and pioneer neurons, for guidance-cue trafficking. We exploit this bottleneck to define roles for glial Netrin and Semaphorin in pioneer- and follower-axon guidance, respectively, and for glial and pioneer-neuron Flamingo (CELSR) in follower-axon navigation. Taken together, our studies reveal previously undescribed glial roles in pioneer-axon guidance, suggesting conserved principles of brain assembly.

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Acknowledgements

We thank C. Bargmann, V. Bertrand, L. Cochella, L. Chen, J. Culotti, O. Hobert, H. Hutter, L. Kutscher, J. Malin, G. Oikonomou, N. Pujol, P. Sengupta, B. Tursun, WG. Wadsworth, S. Wallace, and M. Zhen for reagents, as well as M. Katz for sharing unpublished information. Some strains were provided by the CGC, funded by NIH (P40 OD010440). We thank the Rockefeller University Bio-Imaging and Electron Microscopy Resource Centers for technical help, W.J. Rice at the Simons Electron Microscopy Center (NYSBC) for help with FIB-SEM imaging, and C. Bargmann and the Shaham lab for insights. G.R. was supported by a Shelby White and Leon Levy Foundation fellowship. This work was supported in part by NIH grants NS064273 and NS073121 to S.S.

Author information

Author notes

    • Chang Li
    •  & Alan Shan

    These authors contributed equally to this work.

Affiliations

  1. Laboratory of Developmental Genetics, The Rockefeller University, New York, New York, USA.

    • Georgia Rapti
    • , Chang Li
    • , Alan Shan
    • , Yun Lu
    •  & Shai Shaham

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Contributions

G.R. performed all experiments except the electron microscopy studies, which were performed by Y.L. C.L. and A.S. assisted with generation of plasmids, strains and yeast-two-hybrid screens. S.S. supervised the project. G.R and S.S. wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Georgia Rapti or Shai Shaham.

Integrated supplementary information

Supplementary information

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    Supplementary Text and Figures

    Supplementary Figures 1–8 and Supplementary Tables 1–5

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    Life Sciences Reporting Summary

Excel files

  1. 1.

    Supplementary Table 6

    New mutant alleles generated in this studyGenomic information of the new mutant alleles generated in this study.

  2. 2.

    Supplementary Table 7

    Unstable extra-chromosomal transgenes usedInformation of the unstable extra-chromosomal transgenes generated in this study. Information on allele number, DNA injected and relevant background strain is provided.

  3. 3.

    Supplementary Table 8

    Stably integrated transgenes usedInformation of the stably integrated transgenes used in this study. Information on allele number and relevant citations of published transgenes is provided.

  4. 4.

    Supplementary Table 9

    List of plasmids usedInformation about the plasmids used in this study, as well as citations when applicable, is provided. DNA sequences of pGR plasmids (generated in this study) are available upon request.

  5. 5.

    Supplementary Table 10

    Expression patterns of reporters usedInformation on expression patterns of transgene reporters used in this study is provided. Relevant citations are also provided when applicable.

Videos

  1. 1.

    Head region of wild-type L1 animal reconstructed using FIB-SEM.

    Movie proceeds from posterior to anterior. Bottom right is ventral, top right is left.

  2. 2.

    Head region of kpc-1(gk8); chin-1(ns399) L1 animal reconstructed using FIB-SEM

    Movie proceeds from posterior to anterior. Bottom right is ventral, top right is left.