Identifying suppressors of an alpha-tubulin mutation in C. elegans
Authors:Evan Choate, Mealani Kaiser
Mentor:Renee Baran, Associate Professor of Biology; Advisory Committee of Biochemistry, Occidental College
Microtubules play essential functions in axon outgrowth and axonal transport. However, the mechanisms that regulate microtubule dynamics in developing and mature neurons are poorly understood compared to our knowledge of how microtubules are regulated during cell division. We showed previously that a gain-of-function alpha-tubulin allele, tba-1(ju89), causes defects in motor neuron development and uncoordinated movement. The aim of this study was to identify TBA-1-interacting proteins and potential regulators of microtubule function in neurons. Multiple second-site suppressors of tba-1 (ju89) were isolated in a genetic screen. We focused on four suppressors that we named stub-1-4 (Suppressor of Tubulin mutant defects). The suppressors were mapped to separate chromosomal regions using a SNP (single nucleotide polymorphism) mapping technique. Whole genome sequencing (WGS) and bioinformatics analysis revealed stub-1 was an allele of klp-7 and stub 2 was an allele of zer-1. klp-7 encodes a kinesin-13/MCAK protein. Kinesin-13 proteins are known to regulate microtubule depolymerization. This result suggests that the original ju89 mutation may destabilize neuronal microtubules. zer-1 encodes a substrate recognition subunit of a protein degradation complex not previously associated with microtubule or neuron function. Its substrate is unknown. Our WGS analysis also identified two candidates for stub-3. One candidate is a small GTPase of the Rab family, and the second candidate encodes a lipase. We are conducting transformation rescue experiments to determine if either of these genes is stub-3. stub-4 was mapped to a small region on the C. elegans X chromosome. Additional sequencing and transformation rescue experiments are in progress to identify the gene mutated in the stub-4 strain. Future experiments will address if these suppressors work independently or in concert to regulate microtubule dynamics or transport.