Thesis (Ph.D.). / Written for the Dept. of Biology. Title from title page of PDF (viewed 2009/11/30). Includes bibliographical references.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 134-144). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 134-144). Also available on the Internet.

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In this study, we investigated the mechanism of nitrogen excretion in the soil nematode Caenorhabditis elegans. Utilizing the scanning ion electrode technique (SIET), it was shown for the first time in nematodes that the excretory cell promotes a secretion of ions, including Na+, K+, H+ and Ca2+. In addition, observations from experiments exposing the animal to various environmental pH regimes suggested that the mode of ammonia excretion is dependent on acidification of the unstirred boundary layer, supported also by a detected H+-net-excretion over the hypodermis employing SIET. Pharmacological experiments, SIET and enzyme activity measurements implicated the participation of a functional microtubule network, V-type H+-ATPase, carbonic anhydrase, Na+/K+-ATPase, and apical Na+-channels in the ammonia excretion mechanism of this roundworm. Most importantly, employing ammonia transporter deficient Saccharomyces cerevisiae we were able to show for the first time that an invertebrate Rh-like protein (Rhr-1) does indeed function as an ammonia transporter. Further, a second Rh-protein, Rhr-2, was found to be predominantly expressed in the hypodermis. Knock-out experiments on this transporter further suggested participation of Rhr-2 in the apical ammonia trapping mechanism. Overall, the results of this study provided evidence for a novel ammonia excretion mechanism over the hypodermis, which exhibits features commonly seen in both freshwater (ammonia trapping) and seawater inhabiting species (vesicular transport and exocytosis). / October 2015

Seizures are a symptom of epilepsy, characterized by spontaneous firing due to an imbalance of excitatory and inhibitory features. While mammalian seizure models receive the most attention, the simplicity and tractability of invertebrate model systems, specifically C. elegans and D. melanogaster, have many advantages in understanding the molecular and cellular mechanisms of seizure behavior. This research explores C. elegans and D. melanogaster as electroconvulsive seizure models to investigate methods to both modulate and better understand seizure susceptibility. A common underlying feature of seizures in mammals, worms, and flies involves regulating excitation and inhibition. The C. elegans locomotor circuit is regulated via well characterized GABAergic and cholingeric motoneurons that innervate two rows of dorsal and ventral body wall muscles. In this research, we developed an electroconvulsive seizure assay which utilizes the locomotor circuit as a behavioral read out of neuronal function. When inhibition is decreased in the circuit, for example by decreasing GABAergic input, we find a general increase in the time to recovery from a seizure. After establishing the contribution of excitation and inhibition to seizure recovery, we explored a ubiquitin ligase, associated with comorbidity of an X-linked Intellectual Disorder and epilepsy in humans, and established that the worm homolog, eel-1, contributes to seizure susceptibility similarly to the human gene. Next, we investigated a cGMP-dependent protein kinase (PKG) that functions in the nervous system of both worms and flies and determined that increasing PKG activity, decreases the time to recovery from an electroconvulsive seizure. These experiments suggest a potential novel role for a major protein, PKG, in seizure susceptibility and that the C. elegans and D. melanogaster electroconvulsive seizure assays can be used to investigate possible genes involved in seizure susceptibility and future therapeutic to treat epilepsy. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

The division of one cell to form two cells, or cytokinesis, is fundamental to the development of all known multi-cellular organisms, as well as the propagation of life between generations. The intracellular mechanisms that mediate the physical deformation of the cell membrane during division have proven to be remarkably robust, with multiple processes functioning together to achieve bisection. Here, I present my doctoral work, which seeks to illuminate the dynamic molecular interplay that coordinates and drives cytokinesis in the Caenorhabditis elegans single-cell zygote. In Chapter 1, I begin with an introduction on cytokinesis and the many proteins known to regulate cell division. Chapter 2 presents a detailed review of three intracellular signaling molecules that mediate the spatial control of cytokinesis, known as Rho family small GTPases. In Chapter 3, I present work in which we inactivated specific cytokinesis protein functions at precise stages of the division process, in order to map out the first “temporal atlas” of essential cytokinetic functions. In Chapter 4, I present evidence that the GTPase CDC-42 and the cortical polarity machinery sequester cytokinesis-inhibiting proteins away from the division plane and protect the fidelity of cytokinesis. Chapter 5 lays out preliminary evidence that another GTPase, RAC-1, is a suppresser of cytokinesis and must be inactivated in the division plane specifically by a spindle-associated regulatory protein. Through this body of work, I have attempted to elucidate the underpinnings of the complex intracellular orchestra that drives cytokinesis. This work provides valuable insight, not only into how this vital process occurs, but also how the disruption of its components could lead to the development of complex diseases like cancer.

Age-dependent loss of body wall muscle function and locomotion has been observed in C. elegans, however its cause has yet to be elucidated. Utilizing biochemical techniques and calcium imaging, we demonstrate that aberrant calcium (Ca2+) release via the ryanodine receptor (RyR) homologue UNC-68 contributes to age-dependent muscle weakness in C. elegans. We show that UNC-68 comprises a macromolecular complex bearing FKB-2, a C. elegans immunophilin with high homology to the stabilizing subunit calstabin (calcium channel stabilizing binding protein, or FKBP12). Furthermore, we demonstrate that as the nematode ages, UNC-68 is oxidized and depleted of FKB-2, resulting in “leaky” channels, depleted SR calcium stores, and a reduction in body wall muscle Ca2+ transients at baseline. These perturbations resulted in a motility phenotype, where fkb-2(ok3007) worms harboring a deletion mutation that abolishes FKB-2 binding to the UNC-68 macromolecular complex suffered from poor muscle performance and exercise fatigue in swimming trials. Moreover, pharmacological interventions inducing oxidization of UNC-68 and depletion FKB-2 from the channel independently cause reduced body wall muscle Ca2+ transients, strongly suggesting that UNC-68 oxidation and FKB-2 depletion contribute to muscle function loss observed in aging. UNC-68 oxidation was found to correlate with lifespan, happening earlier in short-lived mitochondrial electron transport chain strains and later in long-lived worms. Finally, preventing FKB-2 depletion from the UNC-68 macromolecular complex in aged C. elegans using the Rycal drug S107 improved muscle Ca2+ transients. Taken together, our data implicate UNC-68 dysfunction in the underlying mechanism of muscle function loss in C. elegans, analogous to observations made of RyR1 dysfunction in aged mammalian skeletal muscle, and describes for the first time a potential role for FKB-2 in C.elegans physiology.