Formation and Function of Ascarosides in the Nematodes C. elegans and C. briggsae

Citation

Cohen, Sarah Michelle (2021) Formation and Function of Ascarosides in the Nematodes C. elegans and C. briggsae. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/84ck-kn25. https://resolver.caltech.edu/CaltechTHESIS:05252021-185133192

Abstract

As an easily culturable, hermaphroditic, and short-lived species with a fully annotated genome and neural connectome, the nematode Caenorhabditis elegans is used as a model organism to study many different biological problems. Examining the communication systems among these worms is important not only to understand how they control and affect one another's behavior, but also gives us clues to the communications systems of closely related parasitic worms.

Nematode worms use small-molecule signaling to send messages about their environments in order to influence behavioral decisions of other animals in their vicinity. A main type of pheromone signaling uses a group of stable small molecules, collectively called ascarosides, that are built modularly from common waste products in cells such as sugars, fatty acids, and amino acid derivatives. Ascarosides are synthesized by C. elegans in precise concentrations and combinations to produce finely-tuned messages which control major behaviors such as mating and entry into dauer, an alternative lifestage that allows worms to survive adverse conditions. We are still unraveling exactly how ascarosides are produced and how they affect behaviors in C. elegans and other worms species.

To further understanding of the formation of ascarosides in C. elegans, I studied the O-acyltransferase gene class to see if they helped catalyze the 4' modifications of ascarosides, as predicted based on their chemistry. Surprisingly, oac genes were found to be uninvolved in the biosynthesis of ascarosides; but they do affect ascaroside production and secretion. To understand the underlying mechanisms of formation and function of ascarosides across worm species, I also studied ascarosides in the closely-related species Caenorhabditis briggsae. First, I developed an efficient CRISPR/Cas9 method for use in C. briggsae. From there, I was able to make the C. briggsae mutants Cbr-glo-1 and Cbr-daf-22, genes that we showed were one-to-one orthologs of their C. elegans counterparts. I then showed that ascr#2 was the main component of daumone in C. briggsae. Additionally, I found that there is an anti-dauer signal, hypothesized to be another type of small signaling molecule – a glucoside. These findings further our understanding of the formation and function of ascaroside signaling molecules in nematode worms.

Thesis Files