The long held view of adherens junctions being a rigid complex has recently been questioned.  At the centre of this is α-catenin and the finding that it can not bind both β-catenin and actin simultaneously.  Isolation of a viable α-catenin mutant in the <i>C. elegans </i>homologue <i>hmp-1 </i>provided an excellent opportunity to study this dogma for the first time in a whole organism.  The work presented in this thesis aimed to characterise this mutation (<i>hmp-1(fe4)</i>) and isolate any potential suppressors of it.  On isolation of suppressors, these were used along with <i>hmp-1(fe4) </i>to investigate α-catenin/<i>hmp-1</i>s role at adherens junctions and how this overlaps with its role in regulating the actin cytoskeleton.  This study has demonstrated that a number of suppressors of <i>hmp-1(fe4) </i>do exist and that they are all intragenic.  In addition, the suppressors are capable of complementing a <i>hmp-1 </i>null strain in <i>hmp-1(fe4)</i>s absence.  Further analysis of these mutations by GFP labelling revealed that these mutations alter the proteins pattern of localisation.  It is thought that this alteration in localisation is the cause for the suppressor’s suppressive effect on <i>hmp-1(fe4).</i> Finally the characterisation of a random <i>C. elegans </i>mutant that arose from the <i>hmp-1(fe4)</i> study but was initially not related to it was later shown to have a synthetic lethal effect when in combination with <i>hmp-1(fe4) </i>and therefore a role that is dependent on a fully function α-catenin/<i>hmp-1.</i>

Oxygen availability is critical for survival for most organisms. The nematode, C. elegans, has been useful for studying genetic regulation of anoxia tolerance due to the oxygen deprivation response mechanisms shared with other metazoans. Studies examining long-term anoxia (72h, LTA) tolerance have only been conducted at adult day 1. To investigate the effect of aging on anoxia tolerance wild-type and mutant strains were exposed to LTA between adult day 1 and day 9. Wild-type isolates and daf-16(mu86) (FOXO transcription factor regulated by insulin-signaling) and aak-2(gt33) (catalytic subunit of AMP-activated protein kinase) strains were anoxia sensitive at day 1 and displayed increased LTA tolerance with aging correlated with reproductive senescence followed by a decline in survivorhsip through day 9. The daf-2(e1370) (insulin receptor homologue of C. elegans), glp-1(e2141) (a lin-12/Notch receptor) and fog-2(q71) (required for spermatogenesis) strains were LTA-tolerant through day 5. I conclude that aging influences LTA-tolerance in a strain- and age-dependent manner. In addition to being LTA-tolerant the daf-2(e1370) and glp-1(e2141) strains have a longevity phenotype that is suppressed by loss of kri-1 or daf-12. While loss of kri-1 did not suppress the LTA-tolerant phenotype of glp-1(e2141) at day 1 the portion of impaired survivors increased at day 3 and by day 5 tolerance was suppressed. Similarly, when exposed to 4 days of anoxia the glp-1(e2141);daf-12(rh41rh611) double mutant had a reduced survivor rate at all ages analyzed compared to glp-1(e2141) controls. To better understand formation of an anoxia-tolerant physiology I exposed adults to one or more 24h bouts. Recurrent bouts increased LTA tolerance in wild-type hermaphrodites in a dose-dependent manner. Bout-treated daf-16(mu86) animals had increased survival rate compared to controls yet maximum survival remained below age-matched wild-type. Anoxia bouts decreased LTA-tolerance in aak-2(gt33) mutants, indicating the requirement for ATP regulation in establishing an LTA-tolerant phenotype. These data support the idea that anoxia tolerance is multi-factorial and influenced by environment, metabolism, food, reproduction, sex phenotype and likely additional factors.

The multifunctional exoribonuclease protein PNPase is implicated as a potential target for cancer therapy as well as causing mitochondrial disorders in humans, but there has yet to be a whole animal knockdown model created. In this study, C. elegans was used to investigate the effect of knocking down pnpt-1, the gene that encodes PNPase. It was discovered that pnpt-1 knockdown significantly extends lifespan via an increase in superoxide production similar to other known mitochondrial lifespan extension pathways. Additionally, mitochondrial networks, size and respiration are affected indication of other mitochondrial dysfunction.. PNPase is also known to transport small RNAs into the mitochondria which in turn can affect mitochondria RNA splicing and translation of proteins involved in respiration. Further investigation showed a significant accumulation of polycistronic mitochondrial transcripts in knockdown animals. Lastly, this model has shown that PNPase knockdown is functionally comparable across species and is a viable model for future studies.

"Microfluidic technologies are popular for biological research, enabling precise physical and chemical control of the microenvironment surrounding living cells and small organisms. Caenorhabditis elegans, a 1 mm long nematode, is capable of olfactory associative learning using the classical conditioning paradigm of pairing an unconditioned stimulus that elicits an innate response, such as food, with a second stimulus, such as an odor, which then elicits a learned behavioral response to this conditioned stimulus alone. Conventional chemotaxis assays on agar petri-plates have been widely used to observe behavioral changes indicative of associative learning; however, reproducibility of these behavioral assays is a major challenge. Here, we describe a microfluidic system that improves the reproducibility of chemotactic behavioral assays by providing better spatiotemporal control of stimuli, gentler worm handling, and more detailed behavioral quantification. Specifically, the microfluidic designs in this study present a uniform conditioning environment followed by a temporally stable linear odor gradient to assess changes to olfactory preference. Stimuli are presented in an enclosed environment to multiple worm populations whose locomotory patterns are analyzed using machine vision. Furthermore, we established an optimized protocol for a positive associative learning paradigm in which animals increase their preference for an odorant, butanone, when previously paired with bacterial food. We reproduced plate-based learning results in wild-type and learning-deficient genetic mutant animals, and demonstrated how developmental stages and chemicals alter the plasticity of olfactory preference. "

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Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 108-118). Also available in electronic version.

Thesis (Ph. D.)--University of Missouri--Columbia, 2001. / "May 2001." Typescript. Vita. Includes bibliographical references (leaves 217-230). Also available on the Internet.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references (leaves 175-187). Also available in electronic version. Access restricted to campus users.