Abundant distribution of TARP gamma-8 in synaptic and extrasynaptic surface of hippocampal neurons and its major role in AMPA receptor expression on spines and dendrites.
Transmembrane alpha-amino-3-hydroxyl-5-isoxazolepropionate (AMPA) receptor regulatory proteins (TARPs) play pivotal roles in AMPA receptor trafficking and gating. Here we examined cellular and subcellular distribution of TARP gamma-8 in the mouse brain. Immunoblot and immunofluorescence revealed the highest concentration of gamma-8 in the hippocampus. Immunogold electron microscopy demonstrated dense distribution of gamma-8 on the synaptic and extrasynaptic surface of hippocampal neurons with very low intracellular labeling. Of the neuronal surface, gamma-8 was distributed at the highest level on asymmetrical synapses of pyramidal cells and interneurons, whereas their symmetrical synapses selectively lacked immunogold labeling. Then, the role of gamma-8 in AMPA receptor expression was pursued in the hippocampus using mutant mice defective in the gamma-8 gene. In the mutant cornu ammonis (CA)1 region, synaptic and extrasynaptic AMPA receptors on dendrites and spines were severely reduced to 35-37% of control levels, whereas reduction was mild for extrasynaptic receptors on somata (74%) and no significant decrease was seen for intracellular receptors within spines. In the mutant CA3 region, synaptic AMPA receptors were reduced mildly at asymmetrical synapses in the stratum radiatum (67% of control level), and showed no significant decrease at mossy fiber-CA3 synapses. Therefore, gamma-8 is abundantly distributed on hippocampal excitatory synapses and extrasynaptic membranes, and plays an important role in increasing the number of synaptic and extrasynaptic AMPA receptors on dendrites and spines, particularly, in the CA1 region. Variable degrees of reduction further suggest that other TARPs may also mediate this function at different potencies depending on hippocampal subregions, input sources and neuronal compartments.
Fukaya
Masahiro
M
Department of Anatomy, Hokkaido University School of Medicine, Sapporo 060-8638, Japan.
Tsujita
Mika
M
Yamazaki
Maya
M
Kushiya
Etsuko
E
Abe
Manabu
M
Akashi
Kaori
K
Natsume
Rie
R
Kano
Masanobu
M
Kamiya
Haruyuki
H
Watanabe
Masahiko
M
Sakimura
Kenji
K
D000818:Animals; D015220:Calcium Channels; D003712:Dendrites / Q000378:metabolism*; D049229:Dendritic Spines / Q000378:metabolism*; D005091:Exons / Q000235:genetics; D019085:Fluorescent Antibody Technique, Direct; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D015151:Immunoblotting; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D009474:Neurons / Q000378:metabolism*; D018091:Receptors, AMPA / Q000096:biosynthesis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013569:Synapses / Q000378:metabolism*
D015220:Calcium Channels; D008565:Membrane Proteins; D018091:Receptors, AMPA; C515550:TARP gamma-8 protein, mouse