Axonal growth and targeting are fundamental to the organization of the nervous system, and require active engagement of the cytoskeleton. Polymerization and stabilization of axonal microtubules is central to axonal growth and maturation of neuronal connectivity. Studies have suggested that members of the tubulin polymerization promoting protein (TPPP, also known as P25α) family are involved in cellular process extension. However, no in vivo knockout data exists regarding its role in axonal growth during development. Here, we report the characterization of Ringmaker (Ringer; CG45057), the only Drosophila homolog of long p25α proteins. Immunohistochemical analyses indicate that Ringer expression is dynamically regulated in the embryonic central nervous system (CNS). ringer-null mutants show cell misplacement, and errors in axonal extension and targeting. Ultrastructural examination of ringer mutants revealed defective microtubule morphology and organization. Primary neuronal cultures of ringer mutants exhibit defective axonal extension, and Ringer expression in cells induced microtubule stabilization and bundling into rings. In vitro assays showed that Ringer directly affects tubulin, and promotes microtubule bundling and polymerization. Together, our studies uncover an essential function of Ringer in axonal extension and targeting through proper microtubule organization.
The authors declare no competing or financial interests.
R.E.M. designed, performed and interpreted experiments, and prepared the manuscript. S.L.R. and A.L.R. performed and interpreted experiments. C.R. performed experiments. S.B. provided reagents and performed analysis. M.A.B. designed and interpreted experiments, and edited the manuscript.
This work was supported by the National Institutes of Health [grant number NS50356 (to M.A.B.)]; the Zachry Foundation; and funds from the State of Texas (M.A.B.). Deposited in PMC for release after 12 months.
Supplementary information available online at http://jcs.biologists.org/lookup/doi/10.1242/jcs.187294.supplemental
- Received February 1, 2016.
- Accepted July 13, 2016.
- © 2016. Published by The Company of Biologists Ltd