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MHCI negatively regulates synapse density during the establishment of cortical connections


Major histocompatibility complex class I (MHCI) molecules modulate activity-dependent refinement and plasticity. We found that MHCI also negatively regulates the density and function of cortical synapses during their initial establishment both in vitro and in vivo. MHCI molecules are expressed on cortical neurons before and during synaptogenesis. In vitro, decreasing surface MHCI (sMHCI) on neurons increased glutamatergic and GABAergic synapse density, whereas overexpression decreased it. In vivo, synapse density was higher throughout development in β2m−/− mice. MHCI also negatively regulated the strength of excitatory, but not inhibitory, synapses and controlled the balance of excitation and inhibition onto cortical neurons. sMHCI levels were modulated by activity and were necessary for activity to negatively regulate glutamatergic synapse density. Finally, acute changes in sMHCI and activity altered synapse density exclusively during early postnatal development. These results identify a previously unknown function for immune proteins in the negative regulation of the initial establishment and function of cortical connections.

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Figure 1: MHCI is present at the surface of cortical neurons before, during and after synapse formation.
Figure 2: Acute β2m knockdown decreases sMHCI and increases glutamatergic and GABAergic synapse density.
Figure 3: Synapse density is increased between visual cortical neurons from β2m−/− mice both in vitro and in vivo throughout development.
Figure 4: MHCI overexpression decreases glutamatergic synapse density.
Figure 5: MHCI bidirectionally regulates glutamatergic and GABAergic synaptic transmission.
Figure 6: Homologous MHCI clusters negatively regulate glutamatergic synapse density.
Figure 7: Changes in MHCI levels are necessary for activity-dependent changes in synapse density.


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We are grateful to M. Edidin (Johns Hopkins University) for the H2-Kb-CFP construct, J. Fritschy (University of Zurich) for antibodies to GABA receptor and J. Trimmer (University of California Davis) for the antibody to PSD-95. We also thank J. Trimmer and E. Diaz (University of California Davis) for advice and for supporting the project. This project was funded by a National Institute for Environmental Health Sciences Training grant (M.W.G.), the John Merck Fund (A.K.M.), the March of Dimes (A.K.M.), Cure Autism Now (A.K.M.), Autism Speaks (A.K.M.) and National Institute of Neurological Disorders and Stroke grant R01NS060125 (A.K.M.). We are especially grateful to the Higgins and Gassin Family Foundations for their invaluable support of basic science research and our work.

Author information




M.W.G. initiated the project, conducted most of the experiments using ICC to measure glutamatergic synapse density and wrote a draft of the manuscript. B.M.E. worked with X.-B.L. to generate and quantify the electron microscopy images. P.A.G. established whole-cell patch-clamp recording and performed all of the electrophysiology experiments. L.A.N. performed essential control experiments for antibody specificity. F.E.-S. performed all of the ICC experiments on GABAergic synapses and most of the TTX and MHC experiments. All of the authors edited the manuscript. A.K.M. supported all aspects of this project, designed and helped to analyze all experiments and wrote the manuscript.

Corresponding author

Correspondence to A Kimberley McAllister.

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The authors declare no competing financial interests.

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Glynn, M., Elmer, B., Garay, P. et al. MHCI negatively regulates synapse density during the establishment of cortical connections. Nat Neurosci 14, 442–451 (2011).

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