CAMSAP2 organizes a gamma-tubulin-independent microtubule nucleation centre through phase separation

Imasaki, Tsuyoshi, Kikkawa, Satoshi, Niwa, Shinsuke, Saijo-Hamano, Yumiko, Shigematsu, Hideki, Aoyama, Kazuhiro, Mitsuoka, Kaoru, Shimizu, Takahiro, Aoki, Mari, Sakamoto, Ayako, Tomabechi, Yuri, Sakai, Naoki, Shirouzu, Mikako, Taguchi, Shinya, Yamagishi, Yosuke, Setsu, Tomiyoshi, Sakihama, Yoshiaki, Nitta, Eriko, Takeichi, Masatoshi, Nitta, Ryo

doi:10.7554/elife.77365

Microtubules are dynamic polymers consisting of αβ-tubulin heterodimers. The initial polymerization process, called microtubule nucleation, occurs spontaneously via αβ-tubulin. Since a large energy barrier prevents microtubule nucleation in cells, the γ-tubulin ring complex is recruited to the centrosome to overcome the nucleation barrier. However, a considerable number of microtubules can polymerize independently of the centrosome in various cell types. Here, we present evidence that the minus-end-binding calmodulin-regulated spectrin-associated protein 2 (CAMSAP2) serves as a strong nucleator for microtubule formation by significantly reducing the nucleation barrier. CAMSAP2 co-condensates with αβ-tubulin via a phase separation process, producing plenty of nucleation intermediates. Microtubules then radiate from the co-condensates, resulting in aster-like structure formation. CAMSAP2 localizes at the co-condensates and decorates the radiating microtubule lattices to some extent. Taken together, these in vitro findings suggest that CAMSAP2 supports microtubule nucleation and growth by organizing a nucleation centre as well as by stabilizing microtubule intermediates and growing microtubules.

CAMSAP2 organizes a gamma-tubulin-independent microtubule nucleation centre through phase separation

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