Abstract
Excitatory synapses are polarized structures that primarily reside on dendritic spines in the brain. The small GTPase Rac1 regulates the development and plasticity of synapses and spines by modulating actin dynamics. By restricting the Rac1-guanine nucleotide exchange factor Tiam1 to spines, the polarity protein Par3 promotes synapse development by spatially controlling Rac1 activation. However, the mechanism for recruiting Par3 to spines is unknown. Here, we identify brain-specific angiogenesis inhibitor 1 (BAI1) as a synaptic adhesion GPCR that is required for spinogenesis and synaptogenesis in mice and rats. We show that BAI1 interacts with Par3/Tiam1 and recruits these proteins to synaptic sites. BAI1 knockdown results in Par3/Tiam1 mislocalization and loss of activated Rac1 and filamentous actin from spines. Interestingly, BAI1 also mediates Rac-dependent engulfment in professional phagocytes through its interaction with a different Rac1-guanine nucleotide exchange factor module, ELMO/DOCK180. However, this interaction is dispensable for BAI1's role in synapse development because a BAI1 mutant that cannot interact with ELMO/DOCK180 rescues spine defects in BAI1-knockdown neurons, whereas a mutant that cannot interact with Par3/Tiam1 rescues neither spine defects nor Par3 localization. Further, overexpression of Tiam1 rescues BAI1 knockdown spine phenotypes. These results indicate that BAI1 plays an important role in synaptogenesis that is mechanistically distinct from its role in phagocytosis. Furthermore, our results provide the first example of a cell surface receptor that targets members of the PAR polarity complex to synapses.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Actins / metabolism
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Analysis of Variance
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Angiogenic Proteins / genetics
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Angiogenic Proteins / metabolism*
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Animals
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Brain / metabolism
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Brain / ultrastructure
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Cadherins / metabolism
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Carrier Proteins / metabolism*
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Cell Adhesion Molecules / metabolism
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Cell Polarity / genetics
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Cells, Cultured
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Disks Large Homolog 4 Protein
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Electric Stimulation
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Electroporation
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Embryo, Mammalian
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Excitatory Postsynaptic Potentials / genetics
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Green Fluorescent Proteins / genetics
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Guanine Nucleotide Exchange Factors / metabolism*
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Hippocampus / cytology
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Humans
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Imaging, Three-Dimensional
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Intracellular Signaling Peptides and Proteins / metabolism
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Membrane Proteins / metabolism
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Microscopy, Confocal
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Microtubule-Associated Proteins / metabolism
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Mutation / genetics
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Neoplasm Proteins / metabolism*
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Nerve Growth Factors / metabolism
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Nerve Tissue Proteins
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Neurons / physiology*
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Patch-Clamp Techniques
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RNA, Small Interfering / metabolism
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Rats
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Rats, Long-Evans
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Receptors, G-Protein-Coupled
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Synapses / metabolism*
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T-Lymphoma Invasion and Metastasis-inducing Protein 1
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Transfection
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Vesicular Glutamate Transport Protein 1 / metabolism
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rac1 GTP-Binding Protein / metabolism
Substances
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ADGRB1 protein, human
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Actins
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Angiogenic Proteins
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Cadherins
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Carrier Proteins
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Cell Adhesion Molecules
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Disks Large Homolog 4 Protein
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Dlg4 protein, rat
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Guanine Nucleotide Exchange Factors
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Intracellular Signaling Peptides and Proteins
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MAP2 protein, rat
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Membrane Proteins
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Microtubule-Associated Proteins
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Neoplasm Proteins
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Nerve Growth Factors
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Nerve Tissue Proteins
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Nfasc protein, rat
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Pard3 protein, rat
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RNA, Small Interfering
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Receptors, G-Protein-Coupled
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T-Lymphoma Invasion and Metastasis-inducing Protein 1
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Tiam1 protein, rat
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Vesicular Glutamate Transport Protein 1
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enhanced green fluorescent protein
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Green Fluorescent Proteins
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rac1 GTP-Binding Protein