| Abstract No.: | C-A3009 |
| Country: | Canada |
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| Title: | LOCALIZATION OF EPHA4 IN POSTNATAL RAT HIPPOCAMPUS |
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| Authors/Affiliations: | 1 Marie-Ève Tremblay*; 1 Mustapha Riad; 1 Guy Doucet;
1 Université de Montréal, Département de pathologie et biologie cellulaire and Groupe de recherche sur le système nerveux central, Université de Montréal, QC, Canada
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| Content: | Interactions between ephrins and their Eph tyrosine kinase receptors play important roles over the course of CNS development. They notably participate in the establishment of somites and rhombomeres, cell migration, axon guidance, and the formation of topographic projection maps. In the hippocampus, recent studies suggest roles in the formation of lamina-specific patterns of connections, synaptogenesis and synaptic plasticity. We examined the cellular and subcellular localization of EphA4 in postnatal day 1 (P1), P7, P14, and P21 rat ventral hippocampus, using light and electron microscopic (EM) immunocytochemistry with a polyclonal antibody against EphA4. The specificity of the antibody was confirmed on brain sections from P7, P14 and adult EphA4 knockout mice. The EphA4 immunoperoxidase labeling was strong, between P1 and P14, in neuropil and cell body layers of CA1 (stratum oriens, stratum radiatum, pyramidal cell layer), CA3 (stratum oriens, stratum lucidum-radiatum and pyramidal cell layer), and the dentate gyrus (inner molecular, polymorphic and granule cell layers). This labeling became weaker in P21 and adult rats, and then concerned essentially the neuropil layers. The present EM analysis was performed in the stratum radiatum and pyramidal cell layer of CA1. At P1 and P7, axon terminals, axonal filopodia, small astrocytic processes, small unmyelinated axons, dendritic branches and filopodia, and myelinated axons were immunolabeled in decreasing order of frequency. Pyramidal cell bodies were labeled on their plasma membrane as well as on the Golgi, endoplasmic reticulum, and vesicles, showing active synthesis and transport of EphA4 at this stage. At P1, spots of labeling were frequent on the plasma membrane of axons or axonal filopodia, in the neighborhood of dendrites or dendritic filopodia. In addition, many labeled perisynaptic astrocytic processes became noticeable at P7, as well as a few dendritic spines. Most labeled axon terminals were in synaptic contact with labeled or unlabeled dendritic shafts, or dendritic spines that were often extending from a labeled dendritic shaft. In axonal filopodia, the immunoperoxidase reaction product was enriched at the sites of contact with dendritic filopodia, representing potential nascent synapses. At P14, filopodia became less numerous whereas dendritic spines increased in numbers. Small, perisynaptic astrocytic processes also increased between P7 and P14. Synaptic contacts between labeled axon terminal and dendritic spine were frequent. Lastly, at P21, EphA4-immunoreactivity mainly concerned axon terminals, small astrocytic processes and dendritic spines, as in the adult (Tremblay et al., 2007). Dendritic shafts and pyramidal cell bodies then became only weakly reactive. At all examined ages, immunogold labeling of EphA4 was located mostly on the plasma membrane of neuronal and astrocytic elements, supporting its availability for surface interactions with ephrins. These observations support a role for EphA4 in dendritic spine formation and synaptogenesis.
Supported by NSERC and an FRSQ infrastructure grant. M.-È.T. is supported by studentships from FRSQ, UdeM, and GRSNC. |
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