Global Analysis of Fission Yeast Mating Genes Reveals New Autophagy Factors

Ling-Ling Sun,Fang Suo,En-Zhi Shen,Meng-Qiu Dong,Wan-Zhong He,Xiao-Man Liu,Bing Yang,Ming Li,Li-Lin Du,Joseph Heitman

doi:10.1371/journal.pgen.1003715

Ling-Ling Sun, Fang Suo + Show 8 more

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https://doi.org/10.1371/journal.pgen.1003715

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Abstract

Macroautophagy (autophagy) is crucial for cell survival during starvation and plays important roles in animal development and human diseases. Molecular understanding of autophagy has mainly come from the budding yeast Saccharomyces cerevisiae, and it remains unclear to what extent the mechanisms are the same in other organisms. Here, through screening the mating phenotype of a genome-wide deletion collection of the fission yeast Schizosaccharomyces pombe, we obtained a comprehensive catalog of autophagy genes in this highly tractable organism, including genes encoding three heretofore unidentified core Atg proteins, Atg10, Atg14, and Atg16, and two novel factors, Ctl1 and Fsc1. We systematically examined the subcellular localization of fission yeast autophagy factors for the first time and characterized the phenotypes of their mutants, thereby uncovering both similarities and differences between the two yeasts. Unlike budding yeast, all three Atg18/WIPI proteins in fission yeast are essential for autophagy, and we found that they play different roles, with Atg18a uniquely required for the targeting of the Atg12–Atg5·Atg16 complex. Our investigation of the two novel factors revealed unforeseen autophagy mechanisms. The choline transporter-like protein Ctl1 interacts with Atg9 and is required for autophagosome formation. The fasciclin domain protein Fsc1 localizes to the vacuole membrane and is required for autophagosome-vacuole fusion but not other vacuolar fusion events. Our study sheds new light on the evolutionary diversity of the autophagy machinery and establishes the fission yeast as a useful model for dissecting the mechanisms of autophagy.

Highlights

Macroautophagy is a catabolic pathway that transports cytoplasmic materials into a degradative organelle, the vacuole or lysosome
The Atg proteins required for all autophagy-related pathways are referred to as the core Atg proteins, and most of them are involved in the generation of a double membrane-enclosed transport vehicle called autophagosome
Ctl1 is required for the normal organization of phagophore assembly site (PAS) To understand how Ctl1 contributes to autophagy, we examined the localization of Atg8 in ctl1D cells

Summary

Introduction

Macroautophagy (hereafter autophagy) is a catabolic pathway that transports cytoplasmic materials into a degradative organelle, the vacuole or lysosome This self-digestion process is upregulated during starvation, when cells have to rely on the turnover of intracellular substances to provide the building blocks for synthesizing new macromolecules [1]. The Atg proteins required for all autophagy-related pathways are referred to as the core Atg proteins, and most of them are involved in the generation of a double membrane-enclosed transport vehicle called autophagosome. The expansion of the autophagosome precursor, called isolation membrane or phagophore, requires the conjugation of a ubiquitin-like protein Atg to phosphatidylethanolamine. Factors involved in this conjugation include the Atg processing enzyme Atg, the E1 enzyme Atg, the E2 enzyme Atg, and the E3-like complex Atg12–Atg5?Atg. Atg is another ubiquitin-like protein whose conjugation to Atg requires the E2 enzyme Atg

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