Toxoplasma gondii :regulation of motility


Fruth, Ingrid A.. (2009). Toxoplasma gondii :regulation of motility. Theses and Dissertations Collection, University of Idaho Library Digital Collections.

Toxoplasma gondii :regulation of motility
Fruth, Ingrid A.
Toxoplasma gondii Microorganisms--Motility
Microbiology, Molecular Biology, and Biochemistry
Recent advances have been made in the identification of the proteins and molecules involved in Toxoplasma gondii activation of motility during invasion and egress-inducing events, however many questions have remained unanswered regarding the regulation and signaling involved during these processes. Previous work clearly shows activation of parasite motility, regardless of whether the parasite is extracellular or intracellular, is greatly influenced by ion fluxes. Considering ions are important second messengers in a number of physiologically important events in many eukaryotic cells, it is not surprising that in T. gondii ions are associated with highly regulated events central to the survival of the parasite, such as invasion and secretion from the parasite's apical organelles. As an obligate intracellular parasite, the physiological function of T. gondii is greatly influenced by the ions and small molecules between it and the host cell within which it resides. This is demonstrated when parasites are incubated in the presence of host cells and simultaneously in a high potassium concentration ([K]) buffer, where they are rendered non-motile and do not invade, despite the fact that inside of a host cell is where the parasite must actively penetrate in order to survive. Or alternatively, in experiments where the host cell [K{esc}p+{esc}s] is specifically decreased upon treatment with nigericin, the parasite will not undergo egress as long as the [K{esc}p+{esc}s] remains buffered at elevated levels similar to that inside of the host cell. These experiments indicate that the parasite actively detects K{esc}p+{esc}s in its surroundings, yet despite this evidence, as far as we know there have yet to be identified T. gondii K{esc}p+{esc}s related proteins specifically involved in this process. Much more is known of the signaling molecules associated with Ca{esc}p2+{esc}s, such as the T. gondii phospholipase C homolog which is suggested to work downstream of events associated with K{esc}p+{esc}s flux.;In addition numerous studies, have demonstrated that T. gondii can be artificially induced to activate motility and that this effect can be readily reproduced using ionophores which permit synchronization of a naturally asynchronous process. With this established system and by using a forward genetics approach to isolate mutants and look for altered gene expression, advances have been made in identifying novel T. gondii genes, such as the isolation of the TgNHE1 parasite, a mutant defective in maintaining Ca{esc}p2{esc}s homeostasis and that does not respond to Ca{esc}p2+{esc}s ionophore-induced egress (IIE). These studies provided evidence for the importance of ion detecting mechanisms and how the parasite responds to its environment. For our experiments we therefore sought use of a forward genetics approach to isolate mutants that have an aberrant response to fluxes in K{esc}p+{esc}s. We were interested in both identifying novel genes involved in parasite activation of motility, despite the presence of a high [K{esc}p+{esc}s] buffer which normally blocks invasion; as well as genes and proteins associated with the detection of K{esc}p+{esc}s and subsequent activation of motility in order to egress from the host cell. Using insertional mutagenesis we isolated mutants from both a genetic selection, testing for mutants which can activate motility and invade host cells irrelevant of incubation in high [K{esc}p+{esc}s] buffer; and also mutants were isolated from a genetic screen which was aimed at isolating and investigating clones that have a defective response to loss of host cell K{esc}p+{esc}s when treated with a K{esc}p+{esc}s-specific ionophore, nigericin.
Thesis (Ph. D., Microbiology, Molecular Biology, and Biochemistry)--University of Idaho, March 2009.
Major Professor:
Gustavo A. Arrizabalaga.
Defense Date:
March 2009.
Format Original:
xi, 188 leaves :col. ill. ;29 cm.

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