Neuroligin1: a cell adhesion molecule that recruits PSD-95 and NMDA receptors by distinct mechanisms during synaptogenesis.
BACKGROUND
The cell adhesion molecule pair neuroligin1 (Nlg1) and beta-neurexin (beta-NRX) is a powerful inducer of postsynaptic differentiation of glutamatergic synapses in vitro. Because Nlg1 induces accumulation of two essential components of the postsynaptic density (PSD) - PSD-95 and NMDA receptors (NMDARs) - and can physically bind PSD-95 and NMDARs at mature synapses, it has been proposed that Nlg1 recruits NMDARs to synapses through its interaction with PSD-95. However, PSD-95 and NMDARs are recruited to nascent synapses independently and it is not known if Nlg1 accumulates at synapses before these PSD proteins. Here, we investigate how a single type of cell adhesion molecule can recruit multiple types of synaptic proteins to new synapses with distinct mechanisms and time courses.


RESULTS
Nlg1 was present in young cortical neurons in two distinct pools before synaptogenesis, diffuse and clustered. Time-lapse imaging revealed that the diffuse Nlg1 aggregated at, and the clustered Nlg1 moved to, sites of axodendritic contact with a rapid time course. Using a patching assay that artificially induced clusters of Nlg, the time course and mechanisms of recruitment of PSD-95 and NMDARs to those Nlg clusters were characterized. Patching Nlg induced clustering of PSD-95 via a slow palmitoylation-dependent step. In contrast, NMDARs directly associated with clusters of Nlg1 during trafficking. Nlg1 and NMDARs were highly colocalized in dendrites before synaptogenesis and they became enriched with a similar time course at synapses with age. Patching of Nlg1 dramatically decreased the mobility of NMDAR transport packets. Finally, Nlg1 was biochemically associated with NMDAR transport packets, presumably through binding of NMDARs to MAGUK proteins that, in turn, bind Nlg1. This interaction was essential for colocalization and co-transport of Nlg1 with NMDARs.


CONCLUSIONS
Our results suggest that axodendritic contact leads to rapid accumulation of Nlg1, recruitment of NMDARs co-transported with Nlg1 soon thereafter, followed by a slower, independent recruitment of PSD-95 to those nascent synapses.
Barrow
Stephanie L
SL
Institute of Neuroscience, University of Oregon, Eugene, Oregon 97403, USA. slbarrow@ucdavis.edu
Constable
John Rl
JR
Clark
Eliana
E
El-Sabeawy
Faten
F
McAllister
A Kimberley
AK
Washbourne
Philip
P
D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D001253:Astrocytes / Q000166:cytology; D019556:COS Cells; D015816:Cell Adhesion Molecules, Neuronal; D002540:Cerebral Cortex / Q000166:cytology*; D002522:Chlorocebus aethiops; D000076122:Disks Large Homolog 4 Protein; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism* / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000502:physiology*; D009474:Neurons / Q000166:cytology; D021381:Protein Transport / Q000235:genetics; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000145:classification / Q000378:metabolism*; D013569:Synapses / Q000502:physiology*; D014162:Transfection / Q000379:methods
D015816:Cell Adhesion Molecules, Neuronal; D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D016194:Receptors, N-Methyl-D-Aspartate; C093438:neuroligin 1; D049452:Green Fluorescent Proteins