Abstract
Doublecortin (DCX) is a neuronal microtubule‐associated protein (MAP) indispensable for brain development. Its flexibly linked doublecortin (DC) domains—NDC and CDC—mediate microtubule (MT) nucleation and stabilization, but it is unclear how. Using high‐resolution time‐resolved cryo‐EM, we mapped NDC and CDC interactions with tubulin at different MT polymerization stages and studied their functional effects on MT dynamics using TIRF microscopy. Although coupled, each DC repeat within DCX appears to have a distinct role in MT nucleation and stabilization: CDC is a conformationally plastic module that appears to facilitate MT nucleation and stabilize tubulin–tubulin contacts in the nascent MT lattice, while NDC appears to be favored along the mature lattice, providing MT stabilization. Our structures of MT‐bound DC domains also explain in unprecedented detail the DCX mutation‐related brain defects observed in the clinic. This modular composition of DCX reflects a common design principle among MAPs where pseudo‐repeats of tubulin/MT binding elements chaperone or stabilize distinct conformational transitions to regulate distinct stages of MT dynamic instability.
Highlights
The highly dynamic and regulated network of microtubules (MTs) in all eukaryotic cells plays numerous critical roles throughout development
We found that only wild-type DCX (WT) and NN efficiently nucleated MTs at 5 lM tubulin concentration—below the ~10 lM critical concentration (Walker et al, 1991)—and that this activity was dosedependent (Fig 1C–F, Appendix Fig S4)
Doublecortin is critical for neuronal motility during mammalian brain development
Summary
The highly dynamic and regulated network of microtubules (MTs) in all eukaryotic cells plays numerous critical roles throughout development. Doublecortin (DCX) is the founding member of the family of MAPs that makes significant contributions to MT regulation in metazoan development (Gonczy et al, 2001; Bechstedt et al, 2010; Fourniol et al, 2013). The Dcx gene is located on chromosome X. It is indispensable for brain development and for migration of immature neurons, such that lack of functional DCX manifests in gray matter heterotopia (females) or lissencephaly (smooth brain; males), causing various degrees of intellectual disability and epilepsy (Gleeson et al, 1998; des Portes et al, 1998). DCX is predominantly expressed in developing brain, it is a marker of adult neurogenesis (Moreno-Jimenez et al, 2019), and in several cancers, where its abnormal expression may promote metastasis by facilitating cell migration (Ayanlaja et al, 2017)
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