Developing high-throughput methods for C. elegans to better understand the newly discovered gasotransmitter sulfur dioxide

Abstract

Sulfur Dioxide (SO 2 ) is the most recently discovered gasotransmitter. As a result there is a significant gap in the literature compared to the other established gasotransmitters which have had several decades of research. Initially, SO 2 was thought to be a toxic air pollutant and byproduct from the metabolism of sulphur containing amino acids. It is thus important to understand its mechanism of action and molecular targets of SO 2 . The pathways for metabolism of sulfur containing gasotransmitters (hydrogen sulfide and sulfur dioxide) in lower organisms was previously unknown. My thesis goal is to gain a better understanding of the function and metabolism of SO 2 . To better elucidate this function I have used the eukaryotic model organisms; Saccharomyces cerevisiae (S. cerevisiae) and Caenorhabditis elegans (C. elegans).Two high-throughput methods were developed as part of this research to improve detail and accuracy of analysis in C. elegans. The first method developed was WormScan, which allowed for automatic whole organism phenotyping. The second method developed was pHi nanoparticles, to enable the characterization of intracellular pH (pHi). These two C. elegans methods were published in PLOS ONE, 2012 and Analytical Biochemistry, 2014. WormScan is based on an affordable consumer grade flatbed scanner that facilitates the quantification of the four main toxicological endpoints of C. elegans and greatly reduces the user bias associated with manual counting. The light intensity produced by the scanner was sufficient to cause negative phototaxis equivalent to a physical stimulus for mortality determination. The affordability and high-throughput nature of WormScan also enable high-throughput whole animal drug screening in C. elegans. The pHi nanoparticles were generated through a modified Stöber synthesis and easily calibrated externally to the C. elegans. The nanoparticles were taken up during feeding, and found to bypass the selective intestinal uptake and translocate to the primary organs and secondary organs of the reproductive tract. This was the first diagnostic use of nanoparticles in C. elegans.It was found that the hypoxia-inducible factor-1 (hif-1) transcription factor was required in order for C. elegans to survive exposure to SO 2 . HIF-1 is a regulator of both pHi homeostasis and metabolic rate. When C. elegans are exposed to a non-lethal concentration of SO 2 , it induced a reversible state of suspended animation, a condition that is characterized by metabolic suppression. A physiologically relevant drop of 0.15 pH units was observed in response to SO 2 exposure. Where such a decrease in pHi is a characteristic of reduced metabolism.II A forward genetic screen was carried out in C. elegans to identify mutations that conferred resistance to SO 2 . A resistance mutation was mapped to a region of Chromosome III using an as yet unpublished high-throughput technique (Mip-Map). Together with whole genome sequencing the gene F08F8.9 causing resistance was identified. The F08F8.9 gene is hom...