title: mTOR is required for asymmetric division through small GTPases in mouse oocytes.
abstract: Mammalian target of rapamycin (mTOR) is central to the control of cell proliferation, growth, and survival in mammalian cells. Prolonged treatment with rapamycin inhibits mTOR complex 2 (mTORC2) activity, and both the mTORC1-mediated S6K1 and 4E-BP1/eIF4E pathways are essential for TORC2-mediated RhoA, Cdc42, and Rac1 expression during cell motility and F-actin reorganization. The functions of mTOR in the mouse oocyte remain unclear, however. The present study shows that rapamycin affects mTOR expression and cytoskeleton reorganization during meiotic maturation of mouse oocytes. mTOR mRNA was expressed in germinal vesicles (GV) until metaphase I (MI), and increased during metaphase II (MII). Immunostaining showed that mTOR localized around the spindle and in the cytoplasm of oocytes. Treatment of oocytes with rapamycin decreased mTOR at the RNA and protein level, and altered asymmetric division. Formation of the actin cap and the cortical granule-free domain were also disrupted after rapamycin treatment, indicating the failure of spindle migration. Injection of an anti-mTOR antibody yielded results consistent with those obtained for rapamycin treatment, further confirming the involvement of mTOR in oocyte polarity. Furthermore, rapamycin treatment reduced the mRNA expression of small GTPases (RhoA, Cdc42, and Rac1), which are crucial regulatory factors for cytoskeleton reorganization. Taken together, these results suggest that rapamycin inhibits spindle migration and asymmetric division during mouse oocyte maturation via mTOR-mediated small GTPase signaling pathways.
authors.affiliation: Department of Animal Sciences, Chungbuk National University, Cheongju, Chungbuk, South Korea.
authors.forename: Seung-Eun
authors.initials: SE
authors.lastname: Lee
authors.forename: Shao-Chen
authors.initials: SC
authors.lastname: Sun
authors.forename: Hyun-Yong
authors.initials: HY
authors.lastname: Choi
authors.forename: Sang-Jun
authors.initials: SJ
authors.lastname: Uhm
authors.forename: Nam-Hyung
authors.initials: NH
authors.lastname: Kim
mesh_terms: D051344:Actin Capping Proteins / Q000096:biosynthesis; D000818:Animals; D049109:Cell Proliferation; D048749:Cytokinesis / Q000187:drug effects; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D059566:M Phase Cell Cycle Checkpoints / Q000187:drug effects; D008677:Metaphase / Q000502:physiology; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D020764:cdc42 GTP-Binding Protein / Q000096:biosynthesis; D020830:rac1 GTP-Binding Protein / Q000096:biosynthesis; D020742:rhoA GTP-Binding Protein / Q000096:biosynthesis
chemical_list: D051344:Actin Capping Proteins; D012333:RNA, Messenger; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein; D020123:Sirolimus