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Autophagy-deficient Schizosaccharomyces pombe mutants undergo partial sporulation during nitrogen starvation

¹ Department of Life Sciences, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa 761-0795, Japan
² Research Center, Asahi Glass Co., Ltd, Kanagawa, Yokohama 221-8755, Japan
³ Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan
⁴ Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan

Autophagy is triggered when organisms sense radical environmental changes, including nutritional starvation. During autophagy, cytoplasmic components, including organelles, are enclosed within autophagosomes and are degraded upon lysosome–vacuole fusion. In this study, we show that processing of GFP-tagged Atg8 can serve as a marker for autophagy in the fission yeast Schizosaccharomyces pombe. Using this marker, 13 Atg homologues were also found to be required for autophagy in fission yeast. In budding yeast, autophagy-deficient mutants are known to be sterile, whereas in fission yeast we found that up to 30 % of autophagy-defective cells with amino acid auxotrophy were able to recover sporulation when an excess of required amino acids was supplied. Furthermore, we found that approximately 15 % of the autophagy-defective cells were also able to sporulate when a prototrophic strain was subjected to nitrogen starvation, which suggested that fission yeast may store sufficient intracellular nitrogen to allow partial sporulation under nitrogen-limiting conditions, although the majority of the nitrogen source is supplied by autophagy. Monitoring of the sporulation process revealed that the process was blocked non-specifically at various stages in the atg1 and atg12 mutants, possibly due to a shortage of amino acids. Taking advantage of this partial sporulation ability of fission yeast, we sought evidence for the existence of a recycling system for nitrogen sources during starvation.

Correspondence
Kaoru Takegawa
takegawa{at}agr.kyushu-u.ac.jp

Two supplementary tables are available with the online version of this paper.

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