The Microtubule Regulator Ringmaker Functions Downstream Of Rtca And The Rna Repair/splicing Pathway To Promote Axon Regeneration

Promoting axon regeneration in the central and peripheral nervous system is of clinical importance in neural injury and neurodegenerative diseases. Both pro- and anti-regeneration factors are being identified. We previously reported that the Rtca mediated RNA repair/splicing pathway restricts axon regeneration by inhibiting the nonconventional splicing of Xbp1 mRNA under cellular stress. Here, we describe the application of a computational screening pipeline used to identify small-molecule inhibitors of Rtca and a paradigm to test for efficacy. However, the downstream effectors of Rtca remain unknown. Through transcriptome profiling, we show that the tubulin polymerization promoting protein (TPPP) – ringmaker/ringer is dramatically increased in Rtca deficient Drosophila sensory neurons, which is dependent on Xbp1. Ringer is expressed in sensory neurons before and after injury, and is cell-autonomously required for axon regeneration. While loss of ringer abolishes the regeneration enhancement in Rtca mutants, its overexpression is sufficient to promote regeneration both in the peripheral and central nervous system. Ringer maintains microtubule stability/dynamics with the microtubule-associated protein – futsch/MAP1B, which is also required for axon regeneration. Furthermore, ringer lies downstream of and is negatively regulated by the microtubule-associated deacetylase – HDAC6, which functions as a regeneration inhibitor. Taken together, our findings suggest that ringer acts as a hub for microtubule regulators that relays cellular status information, such as cellular stress, to the integrity of microtubules in order to instruct neural regeneration.