OVERT AND LATENT PATHWAYS OF POLARITY SPECIFICATION IN ZYGOTES: THE HAPLOID-TO-DIPLOID TRANSITION

Establishment of structural and biochemical asymmetry is fundamental for normal differentiation and function of diverse cell types, from unicellular prokaryotes to multicellular eukaryotes. Polarity specification, the establishment of an axis for directed growth and secretion, allows cells to achieve anasymmetrical state. This phenomenon is conveniently exemplified in the unicellular eukaryote S. cerevisiae, or budding yeast. The nature of the yeast life cycle facilitates the study of polarity specification, as an axis of polarity is established at the beginning of each mitotic cell cycle. The transition from haploid to diploid states involves complex signal transduction cascades, leadingto cell cycle arrest, chemotropic polarized growth, cell-cell fusion and nuclear fusion, culminating in zygote formation. Following substantial remodeling of the cell wall, plasma membrane, and redistribution of cytoplasmic constituents, the newly-minted zygote enters the mitotic cell cycle and must establish a polarization axis for initial bud emergence and growth. Mechanisms of bud siteselection have been characterized in both haploid and diploid mitotic cycles, but the nature of polarity establishment in the zygote remains uncharacterized. This dissertation documents two competing pathways for initial zygotic bud site selection: 1) an overt, medial pathway, independent of the Ras-like GTPase Bud1, and 2) a latent, Bud1-GTPase-dependent, non-medial pathway, elicited bydeletion of the transmembrane protein Rax1 and/or elimination of mitochondrial DNA. In zygotes which lack functional mitochondria, expression of ATP1-111, a mutant of the F1F0-ATPase alpha subunit, largely restores wild-type budding patterns. These observations highlight initial zygotic polarity specification mechanisms as distinct from chemotropic, haploid, and diploid conventions. Insummary, the current investigation describes mechanisms of polarity establishment in the phase of the life cycle immediately following cell-cell fusion and cell cycle re-entry, highlights distinct requirements for initial polarity specification in zygotes, extends the regulatory role of Rax1 in polarity specification, illustrates that Rax1 may influence cytoskeletal polarity independently of Bud1-GTPase activation, and documents a novel linkage between mitochondrial function and cell polarity establishment. In addition, a novel, flow cytometry-based method for zygote purification is described for facilitation of high-throughput, genome-wide studies.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Cell Biology

Grantor dc:publisher

Case Western Reserve University School of Graduate Studies

Year dc:date

2013

Author dc:creator

• Rinonos, Serendipity Zapanta

Contributors dc:contributor

• Tartakoff, Alan
• Manor, Danny

• Cellular Biology
• Molecular Biology
• polarity specification
• cell polarity
• yeast polarity
• bud site selection
• zygotes
• budding yeast

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=case1354902108

OAI identifier oai:identifier

oai:etd.ohiolink.edu:case1354902108