Nectin-dependent localization of synaptic scaffolding molecule (S-SCAM) at the puncta adherentia junctions formed between the mossy fibre terminals and the dendrites of pyramidal cells in the CA3 area of the mouse hippocampus.
BACKGROUND
Two types of intercellular junctions, synaptic junctions (SJs) and puncta adherentia junctions (PAs), are observed at the synapses between the mossy fibre terminals and the dendrites of pyramidal cells in the CA3 area of the hippocampus. SJs are associated with active zones and postsynaptic densities (PSDs) where neurotransmission occurs, whereas PAs are not associated with either of them. We have found that the nectin-afadin unit as well as the N-cadherin-catenin unit localizes at the PAs and that both the units cooperatively organize the PAs. Nectins are Ca2+-independent Ig-like cell-cell adhesion molecules and afadin is a nectin- and actin filament-binding protein that connects nectins to the actin cytoskeleton. Synaptic scaffolding molecule (S-SCAM) is a neural scaffolding protein which interacts with many proteins including neuroligin, NMDA receptors, neural plakophilin-related armadillo-repeat protein/delta-catenin, a GDP/GTP exchange protein for Rap1 small G protein (PDZ-Rap-GEP), and beta-catenin. S-SCAM has been suggested to be a component of PSDs, but its precise localization at the synapses remains unknown.


RESULTS
S-SCAM was not concentrated at the PSDs but highly concentrated and co-localized with nectins at both the sides of the PAs formed between the mossy fibre terminals and the dendrites of pyramidal cells in the CA3 area of the adult mouse hippocampus. S-SCAM co-localized with nectin-1 at the primitive synapses where the SJs and the PAs were not morphologically differentiated, and they co-localized during the maturation of the SJs and the PAs. Nectin-1 had a potency to recruit S-SCAM to the nectin-1-based cell-cell adhesion sites formed in cadherin-deficient L cells as a model system. This recruitment was dependent on the C-terminal PDZ domain-binding motif of nectin-1 which is necessary for the binding of afadin, suggesting that nectins recruit S-SCAM through afadin. Consistently, S-SCAM was co-immunoprecipitated with afadin by the anti-S-SCAM antibody from the mouse brain, but S-SCAM did not directly bind afadin.


CONCLUSIONS
These results indicate that S-SCAM localizes at the PAs in the CA3 area of the hippocampus in a nectin-dependent manner and suggest that S-SCAM serves as a scaffolding molecule at the PAs after maturation of the synapses and at the SJs during the maturation.
Yamada
Akio
A
Department of Molecular Biology and Biochemistry, Osaka University Graduate School of Medicine/Faculty of Medicine, Suita 565-0871, Japan.
Irie
Kenji
K
Deguchi-Tawarada
Maki
M
Ohtsuka
Toshihisa
T
Takai
Yoshimi
Y
D048868:Adaptor Proteins, Signal Transducing; D022005:Adherens Junctions / Q000737:chemistry*; D020816:Amino Acid Motifs; D000818:Animals; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000502:physiology; D002460:Cell Line; D003712:Dendrites / Q000737:chemistry; D051528:Guanylate Kinases; D006624:Hippocampus / Q000737:chemistry / Q000196:embryology; D016547:Kinesins; D051379:Mice; D008807:Mice, Inbred BALB C; D008840:Microfilament Proteins / Q000378:metabolism; D019599:Mossy Fibers, Hippocampal / Q000737:chemistry*; D009218:Myosins; D000075983:Nectins; D011506:Proteins / Q000032:analysis*; D017966:Pyramidal Cells / Q000737:chemistry* / Q000166:cytology; D013569:Synapses / Q000737:chemistry*
D048868:Adaptor Proteins, Signal Transducing; C490657:Afdn protein, mouse; D015815:Cell Adhesion Molecules; D008840:Microfilament Proteins; C000619015:Nectin1 protein, mouse; D000075983:Nectins; D011506:Proteins; C108835:afadin; D051528:Guanylate Kinases; C405684:Magi2 protein, mouse; D009218:Myosins; D016547:Kinesins