A Genome Scale Screen for Mutants with Delayed Exit from Mitosis: Ire1-Independent Induction of Autophagy Integrates ER Homeostasis into Mitotic Lifespan.

Ata Ghavidel,Kunal Baxi,Vladimir Ignatchenko,Terra G Arnason,Troy A A Harkness,Carlos E Carvalho,Martin Prusinkiewicz,Thomas Kislinger,David P Toczyski

doi:10.1371/journal.pgen.1005429

Ata Ghavidel, Kunal Baxi + Show 7 more

Open Access

https://doi.org/10.1371/journal.pgen.1005429

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Journal: PLoS Genetics	Publication Date: Aug 6, 2015
Citations: 68	License type: CC BY 4.0

Affiliation: University of Saskatchewan, University of Toronto

Abstract

Proliferating eukaryotic cells undergo a finite number of cell divisions before irreversibly exiting mitosis. Yet pathways that normally limit the number of cell divisions remain poorly characterized. Here we describe a screen of a collection of 3762 single gene mutants in the yeast Saccharomyces cerevisiae, accounting for 2/3 of annotated yeast ORFs, to search for mutants that undergo an atypically high number of cell divisions. Many of the potential longevity genes map to cellular processes not previously implicated in mitotic senescence, suggesting that regulatory mechanisms governing mitotic exit may be broader than currently anticipated. We focused on an ER-Golgi gene cluster isolated in this screen to determine how these ubiquitous organelles integrate into mitotic longevity. We report that a chronic increase in ER protein load signals an expansion in the assembly of autophagosomes in an Ire1-independent manner, accelerates trafficking of high molecular weight protein aggregates from the cytoplasm to the vacuoles, and leads to a profound enhancement of daughter cell production. We demonstrate that this catabolic network is evolutionarily conserved, as it also extends reproductive lifespan in the nematode Caenorhabditis elegans. Our data provide evidence that catabolism of protein aggregates, a natural byproduct of high protein synthesis and turn over in dividing cells, is among the drivers of mitotic longevity in eukaryotes.

Highlights

Eukaryotic cells undergo a finite number of cell divisions, both in vitro and in vivo, before irreversibly exiting mitosis [1,2]
It is clear that mitotic lifespan is subject to regulation via intricate mechanisms that facilitate exit from mitosis
A High Throughput Screen for Mitotic Longevity Genes in Yeast mitosis is associated with cell immortalization, a hallmark of neoplastic growth

Summary

Introduction

Eukaryotic cells undergo a finite number of cell divisions, both in vitro and in vivo, before irreversibly exiting mitosis [1,2]. Elucidating mechanisms that limit the number of cell divisions has been the subject of intensive research in part because failure to exit mitosis is tightly associated with cell immortalization, a hallmark of neoplastic growth [6]. Large-scale screens of yeast mutants designed to map the underlying longevity networks are reported [4,8]. These screens employed a microdissection assay where daughter cells are successively removed and counted until the mother cells stop dividing. This assay is highly laborious and requires several weeks to complete, limiting its utility as a high throughput screening method. While a valuable genetic resource in dissecting longevity pathways, many of the emerged mutants currently await validation

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