Cytoskeletal rearrangements and crosstalk between microtubules and actin filaments are vital for living organisms. Recently, an abundantly present microtubule polymerase, CKAP5 (XMAP215 homolog), has been reported to play a role in mediating crosstalk between microtubules and actin filaments in the neuronal growth cones. However, the molecular mechanism of this process is unknown. Here, we demonstrate, in a reconstituted system, that CKAP5 enables the formation of persistent actin bundles templated by dynamically instable microtubules. We explain the templating by the difference in CKAP5 binding to microtubules and actin filaments. Binding to the microtubule lattice with higher affinity, CKAP5 enables the formation of actin bundles exclusively on the microtubule lattice, at CKAP5 concentrations insufficient to support any actin bundling in the absence of microtubules. Strikingly, when the microtubules depolymerize, actin bundles prevail at the positions predetermined by the microtubules. We propose that the local abundance of available CKAP5-binding sites in actin bundles allows the retention of CKAP5, resulting in persisting actin bundles. In line with our observations, we found that reducing CKAP5 levels in vivo results in a decrease in actin-microtubule co-localization in growth cones and specifically decreases actin intensity at microtubule plus ends. This readily suggests a mechanism explaining how exploratory microtubules set the positions of actin bundles, for example, in cytoskeleton-rich neuronal growth cones.

Departamento de Ciencias Biológicas y Químicas Facultad de Medicina y Ciencias Universidad San Sebastián Campus Los Leones Lota 2465 Providencia Santiago 7510602 Chile

Department of Cell Biology Faculty of Science Charles University Vinicna 7 Prague 12800 Czech Republic

Department of Medicine Section of Hematology Oncology Boston University and Boston Medical Center Boston MA 02118 USA

Institute of Biotechnology Czech Academy of Sciences BIOCEV Prumyslova 595 Prague West Prague 25250 Czech Republic

Institute of Biotechnology Czech Academy of Sciences BIOCEV Prumyslova 595 Prague West Prague 25250 Czech Republic; Department of Genetics and Microbiology Faculty of Science Charles University Vinicna 7 Prague 12800 Czech Republic

Institute of Biotechnology Czech Academy of Sciences BIOCEV Prumyslova 595 Prague West Prague 25250 Czech Republic; Department of Physical and Macromolecular Chemistry Faculty of Science Charles University Hlavova 8 Prague 12800 Czech Republic

Curr Biol. 2024 Jan 22;34(2):R72-R74. doi: 10.1016/j.cub.2023.12.028. PubMed

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The TOG5 domain of CKAP5 is required to interact with F-actin and promote microtubule advancement in neurons