XMAP215 promotes microtubule–F-actin interactions to regulate growth cone microtubules during axon guidance in Xenopus laevis

Abstract

It has long been established that neuronal growth cone navigation depends on changes in microtubule (MT) and F-actin architecture downstream of guidance cues. However, the mechanisms by which MTs and F-actin are dually coordinated remain a fundamentally unresolved question. Here, we report that the well-characterized MT polymerase, XMAP215 (also known as CKAP5), plays an important role in mediating MT-F-actin interaction within the growth cone. We demonstrate that XMAP215 regulates MT-F-actin alignment through its N-terminal TOG 1-5 domains. Additionally, we show that XMAP215 directly binds to F-actin in vitro and co-localizes with F-actin in the growth cone periphery. We also find that XMAP215 is required for regulation of growth cone morphology and response to the guidance cue, Ephrin A5. Our findings provide the first strong evidence that XMAP215 coordinates MT and F-actin interaction in vivo. We suggest a model in which XMAP215 regulates MT extension along F-actin bundles into the growth cone periphery and that these interactions may be important to control cytoskeletal dynamics downstream of guidance cues. This article has an associated First Person interview with the first author of the paper.

Tau, XMAP215/Msps and Eb1 co-operate interdependently to regulate microtubule polymerisation and bundle formation in axons

“…may explain why loss of XMAP215 was reported to affect MT guidance in growth cones of frog neurons (Slater et al, 2019).…”

“…To assess EB1 comet dynamics and comet amounts, 300 pg of MACF43-Ctail::GFP, an Eb protein-binding 43-residue fragment derived from the C-terminal regions of hMACF2 (human microtubule actin crosslinking factor 2; Fig.3F-F'''; Honnappa, Gouveia et al, 2009, Slater, Cammarata et al, 2019, was co-injected with the MO.…”

The +TIP Navigator-1 is an actin–microtubule crosslinker that regulates axonal growth cone motility

“…For instance, the spectraplakin ACF7/MACF1, the adenomatous polyposis coli (APC) protein, cytoplasmic linker protein (CLIP)-associating proteins (CLASPs), and XMAP215/Colonic and hepatic tumor overexpressed gene (Ch-TOG) are actin-binding +TIPs that can crosslink MTs and actin fibers in the GC ( Coles and Bradke, 2015 ; Cammarata et al, 2016 ). This coupling has been proposed to guide the growth of MTs along preexisting F-actin bundles and control their dynamics ( Hur et al, 2011 ; Koester et al, 2007 ; Purro et al, 2008 ; Slater et al, 2019 ). Besides, mounting evidence in nonneuronal cells also suggests that actin remodeling can be influenced by MT plus ends through APC or CLIP170 via their interaction with the formin mDia1 ( Henty-Ridilla et al, 2016 ; Okada et al, 2010 ).…”

Dynein-mediated microtubule translocation powering neurite outgrowth in chick and Aplysia neurons requires microtubule assembly

“…However, this observation raises the possibility that multiple molecular mechanisms couple MTs to retrograde actin flow. Indeed, there is a growing list of proteins that link MTs to F-actin, including the +TIPs (Marx et al, 2013;Neukirchen and Bradke, 2011;Slater et al, 2019). Perturbation of these molecules does not only affect positioning and orientation of MTs but also influences the organization of the F-actin cytoskeleton and ultimately neurite growth and guidance.…”