Polarized targeting of neurexins to synapses is regulated by their C-terminal sequences.
Two families of cell-adhesion molecules, predominantly presynaptic neurexins and postsynaptic neuroligins, are important for the formation and functioning of synapses in the brain, and mutations in several genes encoding these transmembrane proteins have been found in autism patients. However, very little is known about how neurexins are targeted to synapses and which mechanisms regulate this process. Using various epitope-tagged neurexins in primary hippocampal neurons of wild-type and knock-out mice in vitro and in transgenic animals in vivo, we show that neurexins are trafficked throughout neurons via transport vesicles and the plasma membrane insertion of neurexins occurs preferentially in the axonal/synaptic compartment. We also observed that exit of neurexins from the ER/Golgi and correct targeting require their PDZ-binding motif at the C terminus, whereas two presumptive ER retention signals are inactive. The ubiquitous presence of neurexin-positive transport vesicles and absence of bassoon colabeling demonstrate that these carriers are not active zone precursor vesicles, but colocalization with CASK, RIM1alpha, and calcium channels suggests that they may carry additional components of the exocytotic machinery. Our data indicate that neurexins are delivered to synapses by a polarized and regulated targeting process that involves PDZ-domain mediated interactions, suggesting a novel pathway for the distribution of neurexins and other synaptic proteins.
Fairless
Richard
R
Institute of Anatomy and Molecular Neurobiology, Westfälische Wilhelms-University, D-48149 Münster, Germany.
Masius
Henriette
H
Rohlmann
Astrid
A
Heupel
Katharina
K
Ahmad
Mohiuddin
M
Reissner
Carsten
C
Dresbach
Thomas
T
Missler
Markus
M
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D002135:Calcium-Binding Proteins; D002451:Cell Compartmentation / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D051528:Guanylate Kinases / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D019006:Neural Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D013569:Synapses / Q000378:metabolism* / Q000648:ultrastructure; D013570:Synaptic Membranes / Q000378:metabolism* / Q000648:ultrastructure; D022161:Transport Vesicles / Q000378:metabolism / Q000648:ultrastructure
D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D019006:Neural Cell Adhesion Molecules; C527193:Nrxn1 protein, mouse; C491490:Rims1 protein, mouse; C106868:CASK kinases; D051528:Guanylate Kinases; D019204:GTP-Binding Proteins