To understand how chromosomes are segregated, it is necessary to explain the precise spatiotemporal organization of microtubules (MTs) in the mitotic spindle. We use Xenopus egg extracts to study the nucleation and dynamics of MTs in branched networks, a process that is critical for spindle assembly. Surprisingly, new branched MTs preferentially originate near the minus-ends of pre-existing MTs. A sequential reaction model, consisting of deposition of nucleation sites on an existing MT, followed by rate-limiting nucleation of branches, reproduces the measured spatial profile of nucleation, the distribution of MT plus-ends and tubulin intensity. By regulating the availability of the branching effectors TPX2, augmin and γ-TuRC, combined with single-molecule observations, we show that first TPX2 is deposited on pre-existing MTs, followed by binding of augmin/γ-TuRC to result in the nucleation of branched MTs. In sum, regulating the localization and kinetics of nucleation effectors governs the architecture of branched MT networks

Data availability

All data generated or analyzed during this study are included in the manuscript and supporting files.

Article and author information

Author details

  1. Akanksha Thawani

    Department of Chemical and Biological Engineering, Princeton University, Princeton, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Howard A Stone

    Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, United States
    For correspondence
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-9670-0639
  3. Josh W Shaevitz

    Department of Physics, Princeton University, Princeton, United States
    For correspondence
    Competing interests
    The authors declare that no competing interests exist.
  4. Sabine Petry

    Department of Molecular Biology, Princeton University, Princeton, United States
    For correspondence
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-8537-9763


American Heart Association (17PRE33660328)

  • Akanksha Thawani

National Institute of General Medical Sciences (1DP2GM123493-01)

  • Sabine Petry

Pew Charitable Trusts (00027340)

  • Sabine Petry

David and Lucile Packard Foundation (2014-40376)

  • Sabine Petry

National Science Foundation (PHY-1734030)

  • Josh W Shaevitz

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.


Animal experimentation: This study was performed in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. All of the animals were handled according to approved Institutional Animal Care and Use Committee (IACUC) protocol # 1941-16 of Princeton University.

Reviewing Editor

  1. Raymond E Goldstein, University of Cambridge, United Kingdom

Version history

  1. Received: November 26, 2018
  2. Accepted: May 7, 2019
  3. Accepted Manuscript published: May 8, 2019 (version 1)
  4. Version of Record published: May 15, 2019 (version 2)


© 2019, Thawani et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.


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  1. Akanksha Thawani
  2. Howard A Stone
  3. Josh W Shaevitz
  4. Sabine Petry
Spatiotemporal organization of branched microtubule networks
eLife 8:e43890.

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