title: Fertilization-induced autophagy in mouse embryos is independent of mTORC1.
abstract: Autophagy is a dynamically regulated intracellular degradation system that is important for cellular processes such as amino acid production during starvation and intracellular quality control. Previously, we reported that autophagy is suppressed in oocytes but is rapidly up-regulated after fertilization. During this period, autophagy is thought to be important for the generation of amino acids from the bulk degradation of maternal proteins that have accumulated during oogenesis. However, the mechanism of autophagy induction after fertilization is presently unknown. In most cell types, autophagy is negatively controlled by mammalian target of rapamycin complex 1 (mTORC1), which is typically regulated by amino acids and insulin or related growth factors. In this study, we determined the role of mTORC1 in fertilization-induced autophagy. On the basis of the phosphorylation status of mTORC1 substrates, we found that mTORC1 activity was relatively high in metaphase II (MII) oocytes but was rapidly decreased within 3 h of fertilization. However, chemical inhibition of mTORC1 by Torin1 or PP242 in MII oocytes or fertilized embryos did not induce autophagy. In addition, activation of mTORC1 by cycloheximide did not inhibit fertilization-induced autophagy in fertilized embryos. By contrast, the phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002 effectively suppressed autophagy in these embryos. These data suggest that, even though autophagy induction and postfertilization mTORC1 activity are inversely correlated with each other, as observed in other cell types, mTORC1 suppression is neither essential nor sufficient for fertilization-induced autophagy, highlighting a unique feature of the regulation mechanism of autophagy-mediated intracellular turnover in early embryos.
authors.affiliation: Comprehensive Reproductive Medicine, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan Department of Physiology and Cell Biology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan Laboratory Animal and Genome Sciences Section, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yamamoto
authors.affiliation: Department of Physiology and Cell Biology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan Department of Biochemistry and Molecular Biology, Graduate School and Faculty of Medicine, The University of Tokyo, Tokyo, Japan nmizu@m.u-tokyo.ac.jp.
authors.forename: Noboru
authors.initials: N
authors.lastname: Mizushima
authors.affiliation: Laboratory Animal and Genome Sciences Section, National Institute of Radiological Sciences, Chiba, Japan s_tsuka@nirs.go.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tsukamoto
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D046149:Embryo Culture Techniques; D004622:Embryo, Mammalian / Q000187:drug effects / Q000378:metabolism*; D005306:Fertilization / Q000187:drug effects / Q000502:physiology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009287:Naphthyridines / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: C553294:1-(4-(4-propionylpiperazin-1-yl)-3-(trifluoromethyl)phenyl)-9-(quinolin-3-yl)benzo(h)(1,6)naphthyridin-2(1H)-one; D046912:Multiprotein Complexes; D009287:Naphthyridines; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases
keywords: PtdIns 3-kinase; autophagy; embryo; fertilization; mTOR; mice; signal transduction