Göttingen, University, Diss., 2001. / Text engl.

Göttingen, Universiẗat, Diss., 2003.

Hamburg, Universiẗat, Diss., 2004.

Thesis (Ph. D.)--University of Oregon, 2001. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 118-127). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 100-120).

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 99-113).

Thesis (Ph.D.)--University of Alabama at Birmingham, 2009. / Title from first page of PDF file (viewed on June 11, 2009). Includes bibliographical references.

Proper cell fate specification is crucial for development, and dysregulation in cellular signaling pathways can lead to deleterious effects like cancer. The conserved LIN- 12/Notch signaling pathway mediates fate specification in many cellular contexts, and multiple regulatory mechanisms ensures appropriate LIN-12/Notch activity in each context. Here, I have identified several cis-regulatory domains and trans-acting factors that contribute to the negative regulation of LIN-12/Notch in Caenorhabditis elegans. In this thesis, I find that LIN-12/Notch requires binding to LAG-1/CSL and association with the nuclear complex for protein turnover in the C. elegans vulval precursor cells (VPCs). I also identify two layers of negative regulation in the VPCs and their descendants. The E3 ubiquitin ligase SEL-10/Fbw7 mediates degradation of LIN-12/Notch via the PEST domain in the VPCs, while a novel structural conformation in the C-terminal end of the LIN-12/Notch intracellular domain is required for downregulation in the descendants. Through an RNAi screen for negative regulators, I isolated 13 conserved kinases that downregulate LIN-12/Notch activity. Of these 13 kinases, CDK-8 had been previously implicated in Notch turnover, while the other 12 are novel negative regulators. I provide evidence that 5 of the kinases regulate LIN-12/Notch through modulation of the intracellular domain. Furthermore, I conduct a deeper investigation into CDK-8, which is the kinase component of the Mediator complex. I determine that CDK-8 acts with the rest of the Cdk8 Kinase Module and independent of the Mediator core to negatively regulate LIN-12/Notch, and that CDK-8 kinase activity is required for this process. Lastly, I find that sur-2/MED23 and lin-25/MED24 are required for LIN-12/Notch ligand transcription, independent of the Cdk8 Kinase Module and Mediator Head and Tail components.

Caenorhabditis elegans" locomotion consists of long forward crawling interrupted by short spontaneous reversals. We identified several intrinsic and extrinsic variables that influence the reversal frequency. In particular, reversal frequency can be transiently suppressed by touch. The genes glr-1 and nmr-1, which encode subunits of AMPA- and NMDA-type glutamate receptors, play a central role in touch-induced reversal suppression. Thus, reversal behavior is a motor output reflecting the integration of sensory inputs that display a form of memory. Food has a dramatic effect on reversal frequency that depends on chemosensation. Wild-type worms dramatically reduce reversal frequency on food but chemosensory mutants do not. A null allele of eat-2, a gene necessary for the proper response to food, confers a hyperreversal phenotype. eat-2 also enhances dauer formation in a serotonin deficient genetic background. These phenotypes do not appear to result from the effect of eat-2 on eating efficiency.

clk-1 mutants of the nematode C. elegans have been phenotypically characterized in previous work and found to have decreased rates of development and of periodic adult behaviours, such as defecation, pumping and swimming (Wong et al., 1995). In this study, the defecation periods in older wild type and clk-1 mutant worms were found to be similar despite their differences in young adults. Transgenic strains which express high levels of clk-1 were characterized phenotypically. Over-expression of the clk-1 gene has no observed effect on physiological rates as measured conventionally in young adults but rather has an effect on defecation rates in an age-dependent manner. A proportion of ageing transgenic animals over-expressing clk-1 did not have decreased defecation period, as seen in ageing wild type and clk-1 mutants. This suggests that the action of CLK-1, which functions in controlling physiological rates, is reduced in older wild type worms. As previously characterized, clk-1 mutants have lengthened life spans compared to wild type (Wong et al., 1995). Consistent with this effect, we found transgenic strains with high clk-1 expression to have a shortened average life span. Furthermore, no effect on average life span was found in transgenic control strains in which clk-1 expression was not altered, confirming that the presence of the transgene and the phenotype marking its presence do not influence the observed effects in strains with high clk-1 expression. Together, the findings from both the studies on physiological rates and life span suggest that clk-1 plays a role in determining the rate at which worms age.