ABSTRACT
The mammalian target of rapamycin (mTOR) regulates cell growth in response to various intracellular and extracellular signals. It assembles into two multiprotein complexes: the rapamycin-sensitive mTOR complex 1 (mTORC1) and the rapamycin-insensitive mTORC2. In this study, we inactivated mTORC1 in mice by deleting the gene encoding raptor in the progenitors of the developing CNS. Mice are born but never feed and die within a few hours. The brains deficient for raptor show a microcephaly starting at E17.5 that is the consequence of a reduced cell number and cell size. Changes in cell cycle length during late cortical development and increased cell death both contribute to the reduction in cell number. Neurospheres derived from raptor-deficient brains are smaller, and differentiation of neural progenitors into glia but not into neurons is inhibited. The differentiation defect is paralleled by decreased Stat3 signaling, which is a target of mTORC1 and has been implicated in gliogenesis. Together, our results show that postnatal survival, overall brain growth, and specific aspects of brain development critically depend on mTORC1 function.
Subject(s)
Brain , Cell Differentiation/genetics , Gene Expression Regulation, Developmental/genetics , Microcephaly/genetics , Microcephaly/pathology , Neuroglia/pathology , Proteins/metabolism , Animals , Animals, Newborn , Apoptosis/genetics , Brain/embryology , Brain/growth & development , Brain/pathology , Bromodeoxyuridine/metabolism , Caspase 3/metabolism , Cell Cycle/genetics , Cell Proliferation , Disease Models, Animal , Embryo, Mammalian , Female , Glial Fibrillary Acidic Protein/metabolism , Intermediate Filament Proteins/genetics , Intermediate Filament Proteins/metabolism , Male , Mechanistic Target of Rapamycin Complex 1 , Mice , Mice, Knockout , Microcephaly/mortality , Multiprotein Complexes , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/metabolism , Nestin , Proteins/genetics , STAT3 Transcription Factor/metabolism , TOR Serine-Threonine Kinases , Transcription Factors/genetics , Transcription Factors/metabolism , Tubulin/metabolismABSTRACT
The mammalian target of rapamycin (mTOR) assembles into two distinct multi-protein complexes called mTORC1 and mTORC2. Whereas mTORC1 is known to regulate cell and organismal growth, the role of mTORC2 is less understood. We describe two mouse lines that are devoid of the mTORC2 component rictor in the entire central nervous system or in Purkinje cells. In both lines neurons were smaller and their morphology and function were strongly affected. The phenotypes were accompanied by loss of activation of Akt, PKC, and SGK1 without effects on mTORC1 activity. The striking decrease in the activation and expression of several PKC isoforms, the subsequent loss of activation of GAP-43 and MARCKS, and the established role of PKCs in spinocerebellar ataxia and in shaping the actin cytoskeleton strongly suggest that the morphological deficits observed in rictor-deficient neurons are mediated by PKCs. Together our experiments show that mTORC2 has a particularly important role in the brain and that it affects size, morphology, and function of neurons.
