Abstract
Communication between glial cells and neurons is emerging as a critical parameter of synaptic function. However, the molecular mechanisms underlying the ability of glial cells to modify synaptic structure and physiology are poorly understood. Here we describe a repulsive interaction that regulates postsynaptic morphology through the EphA4 receptor tyrosine kinase and its ligand ephrin-A3. EphA4 is enriched on dendritic spines of pyramidal neurons in the adult mouse hippocampus, and ephrin-A3 is localized on astrocytic processes that envelop spines. Activation of EphA4 by ephrin-A3 was found to induce spine retraction, whereas inhibiting ephrin/EphA4 interactions distorted spine shape and organization in hippocampal slices. Furthermore, spine irregularities in pyramidal neurons from EphA4 knockout mice and in slices transfected with kinase-inactive EphA4 indicated that ephrin/EphA4 signaling is critical for spine morphology. Thus, our data support a model in which transient interactions between the ephrin-A3 ligand and the EphA4 receptor regulate the structure of excitatory synaptic connections through neuroglial cross-talk.
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Acknowledgements
We are grateful to M. Dottori and A. Boyd for providing EphA4 knockout mice, R. Zhou for providing the mouse ephrin-A3 cDNA, D. Melendez for technical assistance, E. Monosov for assistance with confocal microscopy, C. Lennert for advice on statistical analysis and B. Ranscht for critical reading of the manuscript. Supported by the National Institutes of Health (HD25938 and EY10576 to E.B.P. and NS43029 to K.K.M.).
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Supplementary Fig. 1.
Cultured hippocampal neurons lose most EphA4 expression after dissociation and are unaffected by ephrin-A3 stimulation. (a) Dissociated hippocampal neurons at 2 and 3 weeks in vitro do not express detectable levels of EphA4 (green) and are solely labeled for MAP2 (red). At 4 weeks in vitro, only weak diffuse expression of EphA4 is detectable along the entire length of neurites. Ephrin-A3 is also not detected at 2 and 3 weeks in vitro (expression at 4 weeks not determined; scale = 50μm). (b) Hippocampal neurons treated with ephrin-A3 Fc for 45 minutes do not show overt differences in spine morphology compared to Fc-treated neurons (scale = 10μm). (PDF 1118 kb)
Supplementary Fig. 2.
Laser capture microdissection and RT-PCR show that ephrin-A3 mRNA is in astrocytes derived from the neuropil of area CA1. (Top Panel) Captured CA1 pyramidal neurons (N) contain EphA4 mRNA and not mRNA for GFAP (glial-fibrillary acidic protein) or ephrin-A3. β-actin mRNA serves as a positive control. (Middle Panel) Captured astrocytes with interspersed neuronal processes (G + N) contain ephrin-A3 and GFAP mRNA, in addition to EphA4 mRNA. Ephrin-A3 is only detected when GFAP is present. (Lower Panel) Representative example of a tissue section before (left) and after (right) laser capture microdissection. Note: not all cells are lifted off with the procedure. CA1 pyramidal neurons (N) and astrocytes with surrounding neuronal processes (G + N) were taken from approximately 50 sites in each preparation and used to isolate mRNA. (PDF 579 kb)
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Murai, K., Nguyen, L., Irie, F. et al. Control of hippocampal dendritic spine morphology through ephrin-A3/EphA4 signaling. Nat Neurosci 6, 153–160 (2003). https://doi.org/10.1038/nn994
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DOI: https://doi.org/10.1038/nn994
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