Microtubules form dynamic networks in cells and display diverse post-translational modifications (PTMs), including polyglutamylation. The Tubulin Code posits that these PTMs regulate microtubule stability and the properties of molecular motors that use microtubules as tracks for intracellular transport (Verhey and Gaertig, 2007). The enzymes that regulate polyglutamylation are now known: Tubulin tyrosine ligase-like (TTLL) proteins add glutamate side chains, while cytoplasmic carboxypeptidases (CCPs) deglutamylate microtubules (Janke 2011). We sought to find molecules that regulate the PTM enzymes themselves and the downstream molecules that mediate their effects on microtubule stability and traffic.Nematode sensory cilia, which contain highly modified microtubules, provide an ideal model for studying how microtubule PTMs function in vivo. Mutations in
ccpp-1, encoding a CCP deglutamylase, result in progressively degenerating amphid cilia (O'Hagan et al 2011). To identify other molecules that function in polyglutamylation-mediated microtubule stability, we performed a standard EMS F2 Suppressor Screen in C. elegans for novel mutations that suppress the ciliary deterioration of
ccpp-1 mutants. From our screen of over 100,000 haploid genomes, 15 isolates were confirmed to suppress the ciliary degeneration of
ccpp-1.We performed complementation crosses with
ttll-4,
ttll-5, and
ttll-11 mutants, all of which were previously shown to suppress the
ccpp-1 defect. Many suppressors failed to complement mutations in multiple ttll genes. Recently, we found that
ccpp-1 mutant worms that were heterozygous for all three ttll genes showed suppression of the
ccpp-1 mutant phenotype. This is indicative of non-allelic non-complementation and suggests that dosage of TTLL components may be an important factor in maintaining cilium structure. These findings are also consistent with the idea that regulation of glutamylation levels is critical to cilia functionA better understanding of the CCPP-1 pathway and how polyglutamylation controls ciliary and microtubule stability will have important implications for human health, and provide potential drug targets for ciliopathies that cause symptoms such as blindness, respiratory issues, male infertility, and polycystic kidney disease. We hope that identification of our mutations may shed light on ciliopathies for which genetic causes are currently unknown.