title: Physical Interactions and Functional Relationships of Neuroligin 2 and Midbrain Serotonin Transporters.
abstract: The neurotransmitter serotonin [5-hydroxytryptamine (5-HT)] modulates many key brain functions including those subserving sensation, emotion, reward, and cognition. Efficient clearance of 5-HT after release is achieved by the antidepressant-sensitive 5-HT transporter (SERT, SLC6A4). To identify novel SERT regulators, we pursued a proteomic analysis of mouse midbrain SERT complexes, evaluating findings in the context of prior studies that established a SERT-linked transcriptome. Remarkably, both efforts converged on a relationship of SERT with the synaptic adhesion protein neuroligin 2 (NLGN2), a post-synaptic partner for presynaptic neurexins, and a protein well-known to organize inhibitory GABAergic synapses. Western blots of midbrain reciprocal immunoprecipitations confirmed SERT/NLGN2 associations, and also extended to other NLGN2 associated proteins [e.g., α-neurexin (NRXN), gephyrin]. Midbrain SERT/NLGN2 interactions were found to be Ca(2+)-independent, supporting cis vs. trans-synaptic interactions, and were absent in hippocampal preparations, consistent with interactions arising in somatodendritic compartments. Dual color in situ hybridization confirmed co-expression of Tph2 and Nlgn2 mRNA in the dorsal raphe, with immunocytochemical studies confirming SERT:NLGN2 co-localization in raphe cell bodies but not axons. Consistent with correlative mRNA expression studies, loss of NLGN2 expression in Nlgn2 null mice produced significant reductions in midbrain and hippocampal SERT expression and function. Additionally, dorsal raphe 5-HT neurons from Nlgn2 null mice exhibit reduced excitability, a loss of GABAA receptor-mediated IPSCs, and increased 5-HT1A autoreceptor sensitivity. Finally, Nlgn2 null mice display significant changes in behaviors known to be responsive to SERT and/or 5-HT receptor manipulations. We discuss our findings in relation to the possible coordination of intrinsic and extrinsic regulation afforded by somatodendritic SERT:NLGN2 complexes.
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville TN, USA.
authors.forename: Ran
authors.initials: R
authors.lastname: Ye
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville TN, USA.
authors.forename: Meagan A
authors.initials: MA
authors.lastname: Quinlan
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville TN, USA.
authors.forename: Hideki
authors.initials: H
authors.lastname: Iwamoto
authors.affiliation: Department of Psychiatry, Vanderbilt University School of Medicine, Nashville TN, USA.
authors.forename: Hsiao-Huei
authors.initials: HH
authors.lastname: Wu
authors.affiliation: Department of Biological Sciences, Vanderbilt University School of Medicine, Nashville TN, USA.
authors.forename: Noah H
authors.initials: NH
authors.lastname: Green
authors.affiliation: Department of Psychiatry, Vanderbilt University School of Medicine, Nashville TN, USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Jetter
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, NashvilleTN, USA; Department of Biological Sciences, Vanderbilt University School of Medicine, NashvilleTN, USA.
authors.forename: Douglas G
authors.initials: DG
authors.lastname: McMahon
authors.affiliation: Department of Psychiatry, NYS Psychiatric Institute, Columbia University Medical Center, New York NY, USA.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Veestra-VanderWeele
authors.affiliation: Department of Psychiatry, Vanderbilt University School of Medicine, Nashville TN, USA.
authors.forename: Pat
authors.initials: P
authors.lastname: Levitt
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, NashvilleTN, USA; Department of Psychiatry, Vanderbilt University School of Medicine, NashvilleTN, USA.
authors.forename: Randy D
authors.initials: RD
authors.lastname: Blakely
keywords: neurexin; neuroligin2; raphe nucleus; serotonin; transporter