ABSTRACT
The degradation of organelles by autophagy is essential for cellular homeostasis. The Golgi apparatus has recently been demonstrated to be degraded by autophagy, but little is known about how the Golgi is recognized by the forming autophagosome. Using quantitative proteomic analysis and two novel Golgiphagy reporter systems, we found that the five-pass transmembrane Golgi-resident proteins YIPF3 and YIPF4 constitute a Golgiphagy receptor. The interaction of this complex with LC3B, GABARAP, and GABARAPL1 is dependent on a LIR motif within YIPF3 and putative phosphorylation sites immediately upstream; the stability of the complex is governed by YIPF4. Expression of a YIPF3 protein containing a mutated LIR motif caused an elongated Golgi morphology, indicating the importance of Golgi turnover via selective autophagy. The reporter assays reported here may be readily adapted to different experimental contexts to help deepen our understanding of Golgiphagy.
Subject(s)
Adaptor Proteins, Signal Transducing , Autophagy , Golgi Apparatus , Microtubule-Associated Proteins , Golgi Apparatus/metabolism , Humans , Microtubule-Associated Proteins/metabolism , Microtubule-Associated Proteins/genetics , Adaptor Proteins, Signal Transducing/metabolism , Adaptor Proteins, Signal Transducing/genetics , HeLa Cells , Membrane Proteins/metabolism , Membrane Proteins/genetics , Apoptosis Regulatory Proteins/metabolism , Apoptosis Regulatory Proteins/genetics , Proteomics/methods , Membrane Transport Proteins/metabolism , Membrane Transport Proteins/geneticsABSTRACT
The neuron-to-neuron propagation of misfolded α-synuclein (αSyn) aggregates is thought to be key to the pathogenesis of synucleinopathies. Recent studies have shown that extracellular αSyn aggregates taken up by the endosomal-lysosomal system can rupture the lysosomal vesicular membrane; however, it remains unclear whether lysosomal rupture leads to the transmission of αSyn aggregation. Here, we applied cell-based αSyn propagation models to show that ruptured lysosomes are the pathway through which exogenous αSyn aggregates transmit aggregation, and furthermore, this process was prevented by lysophagy, i.e., selective autophagy of damaged lysosomes. αSyn aggregates accumulated predominantly in lysosomes, causing their rupture, and seeded the aggregation of endogenous αSyn, initially around damaged lysosomes. Exogenous αSyn aggregates induced the accumulation of LC3 on lysosomes. This LC3 accumulation was not observed in cells in which a key regulator of autophagy, RB1CC1/FIP200, was knocked out and was confirmed as lysophagy by transmission electron microscopy. Importantly, RB1CC1/FIP200-deficient cells treated with αSyn aggregates had increased numbers of ruptured lysosomes and enhanced propagation of αSyn aggregation. Furthermore, various types of lysosomal damage induced using lysosomotropic reagents, depletion of lysosomal enzymes, or more toxic species of αSyn fibrils also exacerbated the propagation of αSyn aggregation, and impaired lysophagy and lysosomal membrane damage synergistically enhanced propagation. These results indicate that lysophagy prevents exogenous αSyn aggregates from escaping the endosomal-lysosomal system and transmitting aggregation to endogenous cytosolic αSyn via ruptured lysosomal vesicles. Our findings suggest that the progression and severity of synucleinopathies are associated with damage to lysosomal membranes and impaired lysophagy.
Subject(s)
Parkinson Disease , Synucleinopathies , Humans , alpha-Synuclein/metabolism , Macroautophagy , Synucleinopathies/metabolism , Parkinson Disease/metabolism , Lysosomes/metabolismABSTRACT
Membrane rupture of lysosomes results in leakage of their contents, which is harmful to cells. Recent studies have reported that several systems contribute to the repair or elimination of damaged lysosomes. Lysophagy is a type of selective autophagy that plays a crucial role in the lysosomal damage response. Because multiple pathways are involved in this response, an assay that specifically evaluates lysophagy is needed. Here, we developed the TMEM192-mKeima probe to evaluate lysophagy. By comparing the use of this probe with the conventional galectin-3 assay, we showed that this probe is more specific to lysophagy. Using TMEM192-mKeima, we showed that TFEB and p62 are important for the lysosomal damage response but not for lysophagy, although they have previously been considered to be involved in lysophagy. We further investigated the initial steps in lysophagy and identified UBE2L3, UBE2N, TRIM10, 16, and 27 as factors involved in it. Our results demonstrate that the TMEM192-mKeima probe is a useful tool for investigating lysophagy.
Subject(s)
Autophagy , Macroautophagy , Molecular Probes , Autophagy/physiology , Lysosomes/metabolismABSTRACT
Autophagy degrades unnecessary proteins or damaged organelles to maintain cellular function. Therefore, autophagy has a preventive role against various diseases including hepatic disorders, neurodegenerative diseases, and cancer. Although autophagy in germ cells or Sertoli cells is known to be required for spermatogenesis and male fertility, it remains poorly understood how autophagy participates in spermatogenesis. We found that systemic knockout mice of Rubicon, a negative regulator of autophagy, exhibited a substantial reduction in testicular weight, spermatogenesis, and male fertility, associated with upregulation of autophagy. Rubicon-null mice also had lower levels of mRNAs of Sertoli cell-related genes in testis. Importantly, Rubicon knockout in Sertoli cells, but not in germ cells, caused a defect in spermatogenesis and germline stem cell maintenance in mice, indicating a critical role of Rubicon in Sertoli cells. In mechanistic terms, genetic loss of Rubicon promoted autophagic degradation of GATA4, a transcription factor that is essential for Sertoli cell function. Furthermore, androgen antagonists caused a significant decrease in the levels of Rubicon and GATA4 in testis, accompanied by elevated autophagy. Collectively, we propose that Rubicon promotes Sertoli cell function by preventing autophagic degradation of GATA4, and that this mechanism could be regulated by androgens.
Subject(s)
GATA4 Transcription Factor/metabolism , Gene Knockout Techniques/methods , Intracellular Signaling Peptides and Proteins/genetics , Sertoli Cells/physiology , Animals , Autophagy , Cell Line , Fertility , Humans , Male , Mice , Proteolysis , Sertoli Cells/cytology , Single-Cell Analysis , Spermatogenesis , Testis/growth & development , Testis/metabolismABSTRACT
Mitochondrial quality control, which is crucial for maintaining cellular homeostasis, has been considered to be achieved exclusively through mitophagy. Here we report an alternative mitochondrial quality control pathway mediated by extracellular mitochondria release. By performing time-lapse confocal imaging on a stable cell line with fluorescent-labeled mitochondria, we observed release of mitochondria from cells into the extracellular space. Correlative light-electron microscopy revealed that majority of the extracellular mitochondria are in free form and, on rare occasions, some are enclosed in membrane-surrounded vesicles. Rotenone- and carbonyl cyanide m-chlorophenylhydrazone-induced mitochondrial quality impairment promotes the extracellular release of depolarized mitochondria. Overexpression of PRKN (parkin RBR E3 ubiquitin protein ligase), which has a pivotal role in mitophagy regulation, suppresses the extracellular mitochondria release under basal and stress condition, whereas its knockdown exacerbates it. Correspondingly, overexpression of PRKN-independent mitophagy regulators, BNIP3 (BCL2 interacting protein 3) and BNIP3L/NIX (BCL2 interacting protein 3 like), suppress extracellular mitochondria release. Autophagy-deficient cell lines show elevated extracellular mitochondria release. These results imply that perturbation of mitophagy pathway prompts mitochondria expulsion. Presence of mitochondrial protein can also be detected in mouse sera. Sera of PRKN-deficient mice contain higher level of mitochondrial protein compared to that of wild-type mice. More importantly, fibroblasts and cerebrospinal fluid samples from Parkinson disease patients carrying loss-of-function PRKN mutations show increased extracellular mitochondria compared to control subjects, providing evidence in a clinical context. Taken together, our findings suggest that extracellular mitochondria release is a comparable yet distinct quality control pathway from conventional mitophagy.Abbreviations: ACTB: actin beta; ANXA5: annexin A5; ATP5F1A/ATP5A: ATP synthase F1 subunit alpha; ATG: autophagy related; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; CCCP: carbonyl cyanide m-chlorophenylhydrazone; CM: conditioned media; CSF: cerebrospinal fluid; DMSO: dimethyl sulfoxide; EM: electron microscopy; HSPD1/Hsp60: heat shock protein family D (Hsp60) member 1; KD: knockdown; KO: knockout; MAP1LC3A/LC3: microtubule associated protein 1 light chain 3 alpha; MT-CO1: mitochondrially encoded cytochrome c oxidase I; NDUFB8: NADH:ubiquinone oxidoreductase subunit B8; OE: overexpression; OPA1: OPA1 mitochondrial dynamin like GTPase; OXPHOS: oxidative phosphorylation; PBS: phosphate-buffered saline; PB: phosphate buffer; PD: Parkinson disease; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RB1CC1/FIP200: RB1 inducible coiled-coil 1; SDHB: succinate dehydrogenase complex iron sulfur subunit B; TOMM20: translocase of outer mitochondrial membrane 20; TOMM40: translocase of outer mitochondrial membrane 40; UQCRC2: ubiquinol-cytochrome c reductase core protein 2; WT: wild-type.
Subject(s)
Autophagy , Mitophagy , Animals , Autophagy/physiology , Humans , Mice , Mitochondria/metabolism , Mitochondrial Membranes/metabolism , Mitochondrial Proteins/metabolism , Mitophagy/genetics , Ubiquitin-Protein Ligases/metabolismABSTRACT
Sensing and clearance of dysfunctional lysosomes is critical for cellular homeostasis. Here we show that transcription factor EB (TFEB)-a master transcriptional regulator of lysosomal biogenesis and autophagy-is activated during the lysosomal damage response, and its activation is dependent on the function of the ATG conjugation system, which mediates LC3 lipidation. In addition, lysosomal damage triggers LC3 recruitment on lysosomes, where lipidated LC3 interacts with the lysosomal calcium channel TRPML1, facilitating calcium efflux essential for TFEB activation. Furthermore, we demonstrate the presence and importance of this TFEB activation mechanism in kidneys in a mouse model of oxalate nephropathy accompanying lysosomal damage. A proximal tubule-specific TFEB-knockout mouse exhibited progression of kidney injury induced by oxalate crystals. Together, our results reveal unexpected mechanisms of TFEB activation by LC3 lipidation and their physiological relevance during the lysosomal damage response.
Subject(s)
Acute Kidney Injury/pathology , Autophagy , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/metabolism , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/physiology , Lipids/chemistry , Lysosomes/pathology , Microtubule-Associated Proteins/metabolism , Acute Kidney Injury/metabolism , Animals , Autophagy-Related Protein 5/genetics , Autophagy-Related Protein 5/metabolism , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/genetics , Calcium/metabolism , HeLa Cells , Homeostasis , Humans , Lysosomes/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , Microtubule-Associated Proteins/geneticsABSTRACT
The systemic decline in autophagic activity with age impairs homeostasis in several tissues, leading to age-related diseases. A mechanistic understanding of adipocyte dysfunction with age could help to prevent age-related metabolic disorders, but the role of autophagy in aged adipocytes remains unclear. Here we show that, in contrast to other tissues, aged adipocytes upregulate autophagy due to a decline in the levels of Rubicon, a negative regulator of autophagy. Rubicon knockout in adipocytes causes fat atrophy and hepatic lipid accumulation due to reductions in the expression of adipogenic genes, which can be recovered by activation of PPARγ. SRC-1 and TIF2, coactivators of PPARγ, are degraded by autophagy in a manner that depends on their binding to GABARAP family proteins, and are significantly downregulated in Rubicon-ablated or aged adipocytes. Hence, we propose that age-dependent decline in adipose Rubicon exacerbates metabolic disorders by promoting excess autophagic degradation of SRC-1 and TIF2.
Subject(s)
Adipocytes/metabolism , Aging/physiology , Autophagy/genetics , Intracellular Signaling Peptides and Proteins/metabolism , Metabolic Diseases/metabolism , Adipocytes/pathology , Adipogenesis/genetics , Adipose Tissue/cytology , Adipose Tissue/metabolism , Adiposity/genetics , Animals , Apoptosis Regulatory Proteins/metabolism , Autophagy/physiology , Fatty Liver/genetics , Fatty Liver/metabolism , Gene Knockout Techniques , Glucose/genetics , Glucose/metabolism , HEK293 Cells , Humans , Intracellular Signaling Peptides and Proteins/genetics , Lipid Metabolism/genetics , Mice , Mice, Inbred C57BL , Mice, Knockout , Microtubule-Associated Proteins/metabolism , Nuclear Receptor Coactivator 1/metabolism , Nuclear Receptor Coactivator 2/metabolism , PPAR gamma/metabolismABSTRACT
Lipid droplets (LDs) are dynamic organelles that store neutral lipids during times of energy excess, such as after a meal. LDs serve as an energy reservoir during fasting and have a buffering capacity that prevents lipotoxicity. Autophagy and the autophagic machinery have been proposed to play a role in LD biogenesis, but the underlying molecular mechanism remains unclear. Here, we show that when nuclear receptor co-repressor 1 (NCoR1), which inhibits the transactivation of nuclear receptors, accumulates because of autophagy suppression, LDs decrease in size and number. Ablation of ATG7, a gene essential for autophagy, suppressed the expression of gene targets of liver X receptor α, a nuclear receptor responsible for fatty acid and triglyceride synthesis in an NCoR1-dependent manner. LD accumulation in response to fasting and after hepatectomy was hampered by the suppression of autophagy. These results suggest that autophagy controls physiological hepatosteatosis by fine-tuning NCoR1 protein levels.
Subject(s)
Autophagy-Related Protein 7/genetics , Autophagy/genetics , Fatty Liver/metabolism , Nuclear Receptor Co-Repressor 1/metabolism , Animals , Fasting/metabolism , Fatty Acids/biosynthesis , Gene Knockout Techniques , Hep G2 Cells , Humans , Lipid Droplets/metabolism , Lipogenesis/genetics , Liver X Receptors/genetics , Liver X Receptors/metabolism , Mice , Mice, Inbred C57BL , Mice, Knockout , Nuclear Receptor Co-Repressor 1/genetics , Transfection , Triglycerides/biosynthesisABSTRACT
Selective autophagy ensures the removal of specific soluble proteins, protein aggregates, damaged mitochondria, and invasive bacteria from cells. Defective autophagy has been directly linked to metabolic disorders. However how selective autophagy regulates metabolism remains largely uncharacterized. Here we show that a deficiency in selective autophagy is associated with suppression of lipid oxidation. Hepatic loss of Atg7 or Atg5 significantly impairs the production of ketone bodies upon fasting, due to decreased expression of enzymes involved in ß-oxidation following suppression of transactivation by PPARα. Mechanistically, nuclear receptor co-repressor 1 (NCoR1), which interacts with PPARα to suppress its transactivation, binds to the autophagosomal GABARAP family proteins and is degraded by autophagy. Consequently, loss of autophagy causes accumulation of NCoR1, suppressing PPARα activity and resulting in impaired lipid oxidation. These results suggest that autophagy contributes to PPARα activation upon fasting by promoting degradation of NCoR1 and thus regulates ß-oxidation and ketone bodies production.
Subject(s)
Autophagy , Lipid Metabolism , Nuclear Receptor Co-Repressor 1/metabolism , Animals , Autophagy-Related Protein 5/genetics , Autophagy-Related Protein 5/metabolism , Autophagy-Related Protein 5/physiology , Autophagy-Related Protein 7/genetics , Autophagy-Related Protein 7/metabolism , Autophagy-Related Protein 7/physiology , Fasting , Ketone Bodies/metabolism , Liver/metabolism , Mice , Nuclear Receptor Co-Repressor 1/physiology , Oxidation-Reduction , PPAR alphaABSTRACT
Discovery of yeast autophagy-related (ATG) genes and subsequent identification of their homologs in other organisms have enabled researchers to investigate physiological functions of macroautophagy/autophagy using genetic techniques. Specific identification of autophagy-related structures is important to evaluate autophagic activity, and specific ablation of autophagy-related genes is a critical means to determine the requirements of autophagy. Here, we review currently available mouse models, particularly focusing on autophagy (and mitophagy) indicator models and systemic autophagy-related gene-knockout mouse models.
Subject(s)
Autophagy-Related Proteins/genetics , Autophagy/genetics , Autophagy/physiology , Animals , Autophagy-Related Proteins/metabolism , Humans , Mice , Mice, Knockout , Mitochondria/physiology , Mitophagy/genetics , Mitophagy/physiology , Saccharomyces cerevisiae/genetics , Signal Transduction/geneticsABSTRACT
Atg5-null mice are neonatal lethal. We have revealed in our recent paper that these mice die due to neuronal dysfunction resulting in suckling failure. Our new mouse model, atg5-/-;Eno2/Nse-Atg5 mice, where Atg5 is deficient in the whole body except for neurons, enables us to analyze the consequences of macroautophagy/autophagy-deficiency in the whole body of adult mice.
Subject(s)
Aging/metabolism , Autophagy-Related Protein 5/deficiency , Neurons/metabolism , Transgenes , Animals , Animals, Newborn , Autophagy-Related Protein 5/metabolism , Mice, Knockout , Models, Biological , Organ SpecificityABSTRACT
Autophagy is a cytoplasmic degradation system that is important for starvation adaptation and cellular quality control. Previously, we reported that Atg5-null mice are neonatal lethal; however, the exact cause of their death remains unknown. Here, we show that restoration of ATG5 in the brain is sufficient to rescue Atg5-null mice from neonatal lethality. This suggests that neuronal dysfunction, including suckling failure, is the primary cause of the death of Atg5-null neonates, which would further be accelerated by nutrient insufficiency due to a systemic failure in autophagy. The rescued Atg5-null mouse model, as a resource, allows us to investigate the physiological roles of autophagy in the whole body after the neonatal period. These rescued mice demonstrate previously unappreciated abnormalities such as hypogonadism and iron-deficiency anemia. These observations provide new insights into the physiological roles of the autophagy factor ATG5.
Subject(s)
Autophagy-Related Protein 5/deficiency , Neurons/metabolism , Anemia/genetics , Anemia/pathology , Animals , Animals, Newborn , Autophagy-Related Protein 5/metabolism , Brain/metabolism , Gene Expression Regulation, Developmental , Gonadotropins/metabolism , Green Fluorescent Proteins/metabolism , Iron/metabolism , Iron Deficiencies , Male , Mice, Knockout , Organ Specificity , Phosphopyruvate Hydratase/genetics , Promoter Regions, Genetic/genetics , Spermatogenesis , Testosterone/metabolism , Ubiquitinated Proteins/metabolism , UbiquitinationABSTRACT
Protein synthesis inhibitors such as cycloheximide (CHX) are known to suppress protein degradation including autophagy. The fact that CHX inhibits autophagy has been generally interpreted to indicate that newly synthesized protein is indispensable for autophagy. However, CHX is also known to increase the intracellular level of amino acids and activate mTORC1 activity, a master negative regulator of autophagy. Accordingly, CHX can affect autophagic activity through inhibition of de novo protein synthesis and/or modulation of mTORC1 signaling. In this study, we investigated the effects of CHX on autophagy using specific autophagy markers. We found that CHX inhibited starvation-induced autophagy but not Torin1-induced autophagy. CHX also suppressed starvation-induced puncta formation of GFP-ULK1, an early-step marker of the autophagic process which is regulated by mTORC1. CHX activated mTORC1 even under autophagy-inducible starvation conditions. Finally, the inhibitory effect of CHX on starvation-induced autophagy was cancelled by the mTOR inhibitor Torin1. These results suggest that CHX inhibits starvation-induced autophagy through mTORC1 activation and also that autophagy does not require new protein synthesis at least in the acute phase of starvation.
Subject(s)
Autophagy/drug effects , Cycloheximide/pharmacology , Enzyme Activation/drug effects , Multiprotein Complexes/metabolism , Protein Synthesis Inhibitors/pharmacology , TOR Serine-Threonine Kinases/metabolism , Animals , Cell Line , HEK293 Cells , Humans , Mechanistic Target of Rapamycin Complex 1 , Mice , Multiprotein Complexes/antagonists & inhibitors , Naphthyridines/pharmacology , Protein Biosynthesis/drug effects , Starvation/metabolism , TOR Serine-Threonine Kinases/antagonists & inhibitorsABSTRACT
Autophagy is a highly inducible intracellular degradation process. It is generally induced by nutrient starvation and suppressed by food intake. Mammalian (or mechanistic) target of rapamycin complex 1 (mTORC1) is considered to be the major regulator of autophagy, but the precise mechanism of in vivo regulation remains to be fully characterized. Here, we examined the autophagy-suppressive effect of glucose, insulin, and amino acids in the liver and muscle in mice starved for 1 day. Refeeding after starvation with a standard mouse chow rapidly suppressed autophagy in both tissues, and this suppression was inhibited by rapamycin administration almost completely in the liver and partially in muscle, confirming that mTORC1 is indeed a crucial regulator in vivo. As glucose administration showed no major suppressive effect on autophagy, we examined the role of insulin and amino acids using hyperinsulinemic-euglycemic clamp and intravenous amino acid infusion techniques. Insulin administration showed a clear effect on the mTORC1-autophagy pathway in muscle, but had only a very weak effect in the liver. By contrast, amino acids were able to regulate the mTORC1-autophagy pathway in the liver, but less effectively in muscle. These results suggest that autophagy is differentially regulated by insulin and amino acids in a tissue-dependent manner.
Subject(s)
Amino Acids/metabolism , Autophagy , Insulin/metabolism , Liver/metabolism , Multiprotein Complexes/metabolism , Muscle, Skeletal/metabolism , Signal Transduction , TOR Serine-Threonine Kinases/metabolism , Amino Acids/pharmacology , Animals , Autophagy/drug effects , Feeding Behavior/drug effects , Glucose/administration & dosage , Glucose/pharmacology , Humans , Insulin/pharmacology , Liver/cytology , Liver/drug effects , Male , Mechanistic Target of Rapamycin Complex 1 , Mice , Mice, Inbred C57BL , Muscle, Skeletal/cytology , Muscle, Skeletal/drug effects , Signal Transduction/drug effectsABSTRACT
Drastic protein degradation occurs during muscle atrophy induced by denervation, fasting, immobility, and various systemic diseases. Although the ubiquitin-proteasome system is highly up-regulated in denervated muscles, the involvement of autophagy and protein synthesis has been controversial. Here, we report that autophagy is rather suppressed in denervated muscles even under autophagy-inducible starvation conditions. This is due to a constitutive activation of mammalian target of rapamycin complex 1 (mTORC1). We further reveal that denervation-induced mTORC1 activation is dependent on the proteasome, which is likely mediated by amino acids generated from proteasomal degradation. Protein synthesis and ribosome biogenesis are paradoxically increased in denervated muscles in an mTORC1-dependent manner, and mTORC1 activation plays an anabolic role against denervation-induced muscle atrophy. These results suggest that denervation induces not only muscle degradation but also adaptive muscle response in a proteasome- and mTORC1-dependent manner.
Subject(s)
Autophagy , Muscle, Skeletal/physiology , Proteasome Endopeptidase Complex/metabolism , Proteins/metabolism , Animals , Cell Line , Denervation , Mechanistic Target of Rapamycin Complex 1 , Mice , Mice, Inbred C57BL , Multiprotein Complexes , Muscle, Skeletal/innervation , TOR Serine-Threonine KinasesABSTRACT
Autophagy is a major intracellular degradation system in which the cytoplasmic contents are degraded in the lysosome. Its fundamental and evolutionarily conserved role is adaptation to starvation. Recent studies using autophagy-defective mutants of various organisms including mammals have indeed demonstrated the importance of autophagy during starvation; however, the exact mechanism underlying this beneficial effect remains unclear. In addition, it is now apparent that autophagy is also important for cellular homeostasis even under non-starvation conditions, and both non-selective and selective types of autophagy appear to be critical for this function. Here, we discuss the role of this catabolic pathway in recycling intracellular components, with particular reference to nutrient metabolism.
Subject(s)
Autophagy , Metabolic Networks and Pathways , Animals , Cell Physiological Phenomena , Humans , Saccharomyces cerevisiae/cytology , Saccharomyces cerevisiae/physiology , StarvationABSTRACT
After fertilization, the maternal proteins stored in oocytes are degraded and new proteins encoded by the zygotic genome are synthesized. Although several proteins are degraded by the ubiquitin-proteasome system, the mechanism underlying the dynamic protein turnover during this process remains largely unknown. We recently reported that autophagy plays a critical role during preimplantation embryonic development. We found that the level of autophagy was low in unfertilized oocytes; however, autophagy was activated shortly after fertilization. The function of autophagy was further analyzed using oocyte-specific Atg5 (autophagy-related 5) knockout mice. Atg5-null oocytes could develop if they were fertilized with wild-type sperm, but could not develop beyond the four- and eight-cell stages if they were fertilized with Atg5-null sperm. Furthermore, protein synthesis rates were reduced in the autophagy-deficient embryos. We have previously reported that Atg5-null oocytes derived from Atg5(+/-) mice, which should contain maternally inherited Atg5 protein in the oocyte, were able to produce Atg5(-/-) neonates, emphasizing the specific importance of autophagy during very early embryogenesis. Thus, the degradation of maternal factors by autophagy is essential for preimplantation development in mammals.