Engineering and Application of cGAL, a GAL4 Bipartite Expression System for Caenorhabditis elegans

Citation

Liu, Jonathan C. (2019) Engineering and Application of cGAL, a GAL4 Bipartite Expression System for Caenorhabditis elegans. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/V1DD-9108. https://resolver.caltech.edu/CaltechTHESIS:06072019-163128348

Abstract

The core objectives of genetics are to dissect and understand the function of genes, the consequence of their perturbation on an organism, and how their collective action influences an organism’s biology. For genetic model organisms, transgenesis is a tool that allows researchers to introduce synthetic genetic constructs to determine where a gene acts, when it is required, and infer its function. Caenorhabditis elegans is a powerful genetic model organism, with a variety of transgenesis methods available to researchers. Each has its own advantages in speed, efficiency, control of copy number, and control of integration site. However, all methods suffer from issues of reproducibility, reusability, and labor cost. Bipartite systems offer solutions to these issues- they separate the promoter element from the gene product producing strains in which one sex contains the promoter (‘driver’ strain) and the other contains the gene (‘effector’ strain). Crossing driver and effector strains reunites promoter and gene in the progeny, which are assayed and analyzed for gene function. This separation of drivers from effectors allows for a variety of benefits. Driver and effector strains can be combinatorially reused, meaning less time-consuming strain construction. Reusing strains allows for more reproducibility and consistency between experiments and between laboratories. Additionally, novel genes and promoters can be crossed to existing strains for novel transgenic patterns requiring minimal effort. Thus, bipartite systems greatly increase the rigor and pace of genetic analysis. This thesis details the engineering of cGAL, a GAL4-based bipartite system for C. elegans. It uses a novel GAL4 gene from Saccharomyces cerevisiae, a yeast whose optimal growth temperature is similar to that of C. elegans. This thesis also describes an intein-based split bipartite system that offers more refined spatiotemporal control, by allowing two promoters to dictate gene expression instead of one. This split method is used to analyze rhythmic feeding in C. elegans. Finally, engineering of cGAL using single copy methodology is detailed, with a discussion of future improvements to, and usage of, single copy cGAL. This development of a new bipartite system will greatly accelerate genetic analysis for the C. elegans, improve reproducibility for the field, and generate a valuable resource for the community.

Thesis Files