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 are performing complementation tests to determine which suppressors are mutations in ttll genes and whole genome sequencing to identify causal mutations.A better understanding of the CCPP-1 pathway and how polyglutamylation controls ciliary and microtubule stability will have important implications for human health and will provide potential drug targets for ciliopathies, which cause blindness, respiratory issues, male infertility, and polycystic kidney disease in humans. We hope that identification of our mutations may shed light on ciliopathies for which genetic causes are currently unknown.