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Eisosomes organize the plasma membrane of yeast / by Ruth V. Kabeche

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Author	Kabeche, Ruth V.
Title	Eisosomes organize the plasma membrane of yeast / by Ruth V. Kabeche
Date	2015
Abstract	The cortical cytoskeleton mediates a range of cellular activities such as endocytosis, cell motility, and the maintenance of cell rigidity. In yeast cells, prominent cortical structures called eisosomes generate specialized domains termed MCCs to cluster specific proteins at sites of membrane invaginations. Here, I show that the core eisosome protein Pil1 forms linear cortical filaments in fission yeast cells, and that purified Pil1 assembles into filaments in vitro. The transmembrane protein Fhn1 and the peripheral membrane protein Sle1 co-localize and are interdependent with Pil1 for localization to cortical filaments. Increased Pil1 expression leads to cytoplasmic Pil1 rods that detach from the plasma membrane and contain crosslinked Pil1 tubules that display regular, hexagonal spacing. Through a series of genetic screens in fission yeast, we found that the eisosome proteins Pil1 and Sle1 function with the synaptojanin-like lipid phosphatase Syj1 and its ligand Tax4. This functional module connects eisosome function with PI(4,5)P2 hydrolysis in cells. Mutations in the Pil1-Sle1-Syj1-Tax4 module suppress the growth and morphology defects of TORC2 mutants, indicating that eisosome-dependent regulation of PI(4,5)P? feeds into signal transduction pathways. Eisosomes and PI(4,5)P2 regulate TORC2 via the cell integrity pathway, as suppression of TORC2 mutants by the removal of eisosomes requires a functional cell integrity pathway. When cells are osmotically stressed, PI(4,5)P2 is spatially relocalized to clusters on the plasma membrane. These clusters are required for cell integrity pathway activation and for the proper redistribution of signaling proteins. Furthermore, eisosomes regulate PI(4,5)P? clusters upon osmotic stress ultimately regulating the cell integrity pathway. Eisosomes have a biochemical role in stress signal transduction pathways, however they also have a mechanical role for cellular stress response. When cells are exposed to hypo-osmotic shock there is a rapid influx of water resulting in cellular expansion. Cells lacking eisosomes lyse at a faster rate than wildtype cells. Without a cell wall, eisosomes disassemble from the plasma membrane resulting in a dramatic increase in cell size. We propose that the geometry of membrane invaginations generates spatial and temporal signals for lipid-mediated signaling events in cells. My combined studies have shown that eisosomes organize the yeast plasma membrane and feed into cell signaling pathways, specifically the osmotic stress response, through the regulation of PI(4,5)P2.
Description	1 online resource (xiv, 193 pages) : illustrations (mostly color)
Format	application/pdf
College	Geisel School of Medicine at Dartmouth -- Department of Biochemistry.
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Copyright	All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means without permission in writing from the author.
DOI	http://dx.doi.org/10.1349/ddlp.1915

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