LRRTMs and neuroligins bind neurexins with a differential code to cooperate in glutamate synapse development.
Leucine-rich repeat transmembrane neuronal proteins (LRRTMs) were recently found to instruct presynaptic and mediate postsynaptic glutamatergic differentiation. In a candidate screen, here we identify neurexin-1beta lacking an insert at splice site 4 (-S4) as a ligand for LRRTM2. Neurexins bind LRRTM2 with a similar affinity but distinct code from the code for binding neuroligin-1 (the predominant form of neuroligin-1 at glutamate synapses, containing the B splice site insert). Whereas neuroligin-1 binds to neurexins 1, 2, and 3 beta but not alpha variants, regardless of insert at splice site 4, LRRTM2 binds to neurexins 1, 2, and 3 alpha and beta variants specifically lacking an insert at splice site 4. We further show that this binding code is conserved in LRRTM1, the family member linked to schizophrenia and handedness, and that the code is functional in a coculture hemisynapse formation assay. Mutagenesis of LRRTM2 to prevent binding to neurexins abolishes presynaptic inducing activity of LRRTM2. Remarkably, mutagenesis of neurexins shows that the binding face on neurexin-1beta (-S4) is highly overlapping for the structurally distinct LRRTM2 and neuroligin-1 partners. Finally, we explore here the interplay of neuroligin-1 and LRRTM2 in synapse regulation. In neuron cultures, LRRTM2 is more potent than neuroligin-1 in promoting synaptic differentiation, and, most importantly, these two families of neurexin-binding partners cooperate in an additive or synergistic manner. Thus, we propose a synaptic code hypothesis suggesting that neurexins are master regulators of the cooperative activities of LRRTMs and neuroligins.
Siddiqui
Tabrez J
TJ
Brain Research Centre, Department of Psychiatry, University of British Columbia, Vancouver, British Columbia, Canada.
Pancaroglu
Raika
R
Kang
Yunhee
Y
Rooyakkers
Amanda
A
Craig
Ann Marie
AM
D017398:Alternative Splicing / Q000235:genetics; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D003164:Competitive Bidding / Q000379:methods; D004622:Embryo, Mammalian; D018698:Glutamic Acid / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics; D006624:Hippocampus / Q000166:cytology; D006801:Humans; D016296:Mutagenesis / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D019006:Neural Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000502:physiology*; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013569:Synapses / Q000502:physiology*; D014162:Transfection / Q000379:methods
D015816:Cell Adhesion Molecules, Neuronal; C485182:Cyan Fluorescent Protein; C547192:LRRTM2 protein, rat; D009419:Nerve Tissue Proteins; D019006:Neural Cell Adhesion Molecules; D020033:Protein Isoforms; D021122:Protein Subunits; C093438:neuroligin 1; D049452:Green Fluorescent Proteins; D018698:Glutamic Acid; D002118:Calcium