Distinct effects of tubulin isotype mutations on neurite growth inCaenorhabditis elegans

Abstract

. CC-BY 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/131326 doi: bioRxiv preprint first posted online Apr. 26, 2017; 3 Abstract 89 Tubulins, the building block of microtubules (MTs), play a critical role in both supporting and 90 regulating neurite growth. Eukaryotic genomes contain multiple tubulin isotypes, and their 91 missense mutations cause a range of neurodevelopmental defects. Using the C. elegans touch 92 receptor neurons, we analyzed the effects of 67 tubulin missense mutations on neurite growth. 93Three types of mutations emerged: 1) loss-of-function mutations, which cause mild defects in 94 neurite growth; 2) antimorphic mutations, which map to the GTP binding site and intradimer and 95 interdimer interfaces, significantly reduce MT stability, and cause severe neurite growth defects; 96 and 3) neomorphic mutations, which map to the exterior surface, increase MT stability, and 97 cause ectopic neurite growth. Structure-function analysis reveals a causal relationship between 98 tubulin structure and MT stability. This stability affects neuronal morphogenesis. As part of this 99 analysis, we engineered several disease-associated human tubulin mutations into C. elegans 100 genes and examined their impact on neuronal development at the cellular level. We also 101 discovered an α-tubulin (TBA-7) that appears to destabilize MTs. Loss of TBA-7 led to the 102 formation of hyperstable MTs and the generation of ectopic neurites; the lack of potential sites 103 for polyamination and polyglutamination on TBA-7 may be responsible for this destabilization. al., 2011; Prokop, 2013; Sainath and Gallo, 2015). MTs constantly explore the growth cone 114 periphery until they are captured by stabilized actin filaments or membrane receptors enriched at 115 the side of the growth cone responding to a guidance cue (Tanaka et al., 1995; Challacombe et 116 al., 1996; Schaefer et al., 2008; Qu et al., 2013). This capture transiently stabilizes MTs and 117 enables MT elongation in the direction that the growth cone has turned. In addition to providing 118 physical support for the neurite growth that follows the changes in actin dynamics, MTs also 119 play an instructive role in neurite guidance. Since local application of the MT-stabilizing drug 120 paclitaxel (also known as taxol) induced growth cone attraction, of the MT-destabilizing drug 121 nocodazole induced repulsion, and of the MT-depolymerizing drug colchicine resulted in 122 branching (Bray et al., 1978; Buck and Zheng, 2002), signals that act by altering MT stability 123 appear to directly initiate growth cone turning. Indeed, the guidance molecule Wnt can induce 124 growth cone remodeling by changing the organization of MT structure through the inactivation 125 of MT-plus end binding protein Adenomatous Polyposis Coli (Purro et al., 2008). These results 126 indicate that the regulation of MT dynamics is crucial for neurite growth an...

Glutamylation Regulates Transport, Specializes Function, and Sculpts the Structure of Cilia

“…Possibly, TBA-6 insertion into the MT lattice in CEM cilia fine-tunes glutamylation to regulate the doublet-to-singlet transition. Particular tubulins have been found to be important for protofilament number and MT structure in C. elegans non-ciliated touch receptor neurons [47, 48]. Our results, together with previous findings, support the Tubulin Code hypothesis [12], in that tubulin function can be specialized by PTMs such as glutamylation.…”

Axonal plasticity in response to active forces generated through magnetic nanopulling

“…1B1, p =0.49), suggesting that the C. elegans neurons lacking α-tubulin do not respond to the nano-pulling. To corroborate the findings with MEC-12, we used a mutant strain with a mec-7 allele in touch receptor neurons that lacks stable 15 protofilament MTs but still forms small diameter 11 protofilament MTs (Zheng et al, 2017). We reasoned that MTs are destabilized at higher temperatures (16°C vs 25°C), due to their faster depolymerization rate at 25°C (Li and Moore, 2020).…”