title: Neuronal major histocompatibility complex class I molecules are implicated in the generation of asymmetries in hippocampal circuitry.
abstract: Left-right asymmetry is a fundamental feature of higher-order brain function; however, the molecular basis of brain asymmetry has remained unclear. We have recently demonstrated asymmetries in hippocampal circuitry resulting from the asymmetrical allocation of NMDA receptor (NMDAR) subunit GluR2 (NR2B) in pyramidal cell synapses. This asymmetrical allocation of 2 subunits affects the properties of NMDARs and generates two populations of synapses, '2-dominant' and '2-non-dominant' synapses, according to the hemispheric origin of presynaptic inputs and cell polarity of the postsynaptic neurone. To identify key regulators for generating asymmetries, we analysed the hippocampus of β2-microglobulin (β2m)-deficient mice lacking cell surface expression of major histocompatibility complex class I (MHCI). Although MHCI proteins are well known in the immune system, accumulating evidence indicates that MHCI proteins are expressed in the brain and are required for activity-dependent refinement of neuronal connections and normal synaptic plasticity. We found that β2m proteins were localised in hippocampal synapses in wild-type mice. NMDA EPSCs in β2m-deficient hippocampal synapses receiving inputs from both hemispheres showed similar sensitivity to Ro 25-6981, an 2 subunit-selective antagonist, with those in '2-dominant' synapses for both the apical and basal synapses of pyramidal neurones. The structural features of the β2m-deficient synapse in addition to the relationship between the stimulation frequency and synaptic plasticity were also comparable to those of '2-dominant' synapses. These observations indicate that the β2m-deficient hippocampus lacks '2-non-dominant' synapses and circuit asymmetries. Our findings provide evidence supporting a critical role of MHCI molecules for generating asymmetries in hippocampal circuitry.
authors.affiliation: I. Ito: Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan. isitoscb@kyushu-u.org.
authors.forename: Aiko
authors.initials: A
authors.lastname: Kawahara
authors.forename: Shotaro
authors.initials: S
authors.lastname: Kurauchi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fukata
authors.forename: José
authors.initials: J
authors.lastname: Martínez-Hernández
authors.forename: Terumi
authors.initials: T
authors.lastname: Yagihashi
authors.forename: Yuya
authors.initials: Y
authors.lastname: Itadani
authors.forename: Rui
authors.initials: R
authors.lastname: Sho
authors.forename: Taiichi
authors.initials: T
authors.lastname: Kajiyama
authors.forename: Nao
authors.initials: N
authors.lastname: Shinzato
authors.forename: Kenji
authors.initials: K
authors.lastname: Narusuye
authors.forename: Masaki
authors.initials: M
authors.lastname: Fukata
authors.forename: Rafael
authors.initials: R
authors.lastname: Luján
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Shigemoto
authors.forename: Isao
authors.initials: I
authors.lastname: Ito
mesh_terms: D000818:Animals; D019706:Excitatory Postsynaptic Potentials; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009473:Neuronal Plasticity; D010636:Phenols / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D021381:Protein Transport; D017966:Pyramidal Cells / Q000378:metabolism* / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000378:metabolism; D013569:Synapses / Q000378:metabolism / Q000502:physiology*; D001613:beta 2-Microglobulin / Q000235:genetics / Q000378:metabolism
chemical_list: D015395:Histocompatibility Antigens Class I; C121001:NR2B NMDA receptor; D010636:Phenols; D010880:Piperidines; D016194:Receptors, N-Methyl-D-Aspartate; C109643:Ro 25-6981; D001613:beta 2-Microglobulin