Date of Award

Spring 2015

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Abbot, Allison

Second Advisor

Petrella, Lisa

Third Advisor

Blumenthal, Edward

Abstract

Rhythmic behaviors are ubiquitous phenomena in plant and animal phyla. Ultradian rhythmic behaviors occur with a period of less than 24 hours and include such rhythmic behaviors as the beating of the heart and peristalsis in the gut. The nematode C. elegans exhibits three well-characterized ultradian rhythmic behaviors: ovulation, pharyngeal pumping, and the defecation motor program (DMP). The DMP occurs every ~45 seconds in wild-type worms and comprises three distinct muscle contractions: a posterior body contraction (pBoc), an anterior body contraction (aBoc), and an enteric muscle contraction (Emc), which is coupled to expulsion (Exp). The rhythmicity of the DMP is Ca2+-dependent, meaning fluctuations in intracellular Ca2+ levels in the pacemaker cell regulate the behavior. A forward genetic screen was performed to identify genes necessary for proper pacemaker function (Iwasaki et al., 1995). One of the mutants isolated, dec-11, lacks pacemaker activity and displays long and irregular defecation cycles. However, the gene mutated in dec-11 worms has not been identified. In order to determine the function of the dec-11 gene in the control of pacemaker activity for the DMP, genetic analysis and video microscopy were utilized. First, genetic analysis was performed to test whether dec-11 acts upstream of IP3 mediated Ca2+ release using mutations in ipp-5 and lfe-2, which encode an IP3 phosphatase and an IP3 kinase respectively. dec-11;ipp-5 and dec-11;lfe-2 double mutants both showed partial suppression of the irregular defecation cycle phenotype characteristic of dec-11 single mutants. Additionally, when dec-11 worms were grown on high Mg2+ plates, the irregular defecation cycles were suppressed, suggesting a role for dec-11 in the regulation of the DMP. Parallel work using SNP interval mapping and whole-genome sequencing has allowed us to identify a molecular interval in which dec-11 is located and to generate a list of candidate genes. Additionally, RNAi analysis of candidate genes will allow us to determine the molecular identity of dec-11. Taken together these data are consistent with a model that places the function of dec-11 in the regulation of the initiating event of the DMP.

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