Neuroligin1 Drives Synaptic and Behavioral Maturation through Intracellular Interactions

Abstract

In vitro studies suggest that the intracellular C-terminus of Neuroligin1 (NL1) could play a central role in the maturation of excitatory synapses. However, it is unknown how this activity affects synapses in vivo, and whether it may impact the development of complex behaviors. To determine how NL1 influences the state of glutamatergic synapses in vivo, we compared the synaptic and behavioral phenotypes of mice overexpressing a full length version of NL1 (NL1FL) with mice overexpressing a version missing part of the intracellular domain (NL1ΔC). We show that overexpression of full length NL1 yielded an increase in the proportion of synapses with mature characteristics and impaired learning and flexibility. In contrast, the overexpression of NL1ΔC increased the number of excitatory postsynaptic structures and led to enhanced flexibility in mnemonic and social behaviors. Transient overexpression of NL1FL revealed that elevated levels are not necessary to maintain synaptic and behavioral states altered earlier in development. In contrast, overexpression of NL1FL in the fully mature adult was able to impair normal learning behavior after one month of expression. These results provide the first evidence that NL1 significantly impacts key developmental processes that permanently shape circuit function and behavior, as well as the function of fully developed neural circuits. Overall, these manipulations of NL1 function illuminate the significance of NL1 intracellular signaling in vivo, and enhance our understanding of the factors that gate the maturation of glutamatergic synapses and complex behavior. This has significant implications for our ability to address disorders such as ASD.

Developmental expression of the neuroligins and neurexins in fragile X mice

“…In addition, sex differences in gene expression were observed in both WT and FMR1‐KO mice; however, the genes that showed sex differences in mRNA expression in WT mice were distinct from the those showing sex differences in FMR1‐KO mice, reinforcing the importance of including both sexes in animal studies. Overall, these data, along with characterizations of the neuroligin (Blundell et al, ; Hoy et al, ; Jamain et al, ; Jaramillo et al, ; Tabuchi et al, ; Wohr et al, ) and neurexin (Etherton et al, ; Grayton et al, ; Ju et al, ; Rabaneda et al, ) mutant mouse models, suggest that deficits in this gene family may be an important contributor to brain and behavioral changes in FMR1‐KO mice.…”

“…For instance, the expression profile of NLGN1 that we observed coincides with the timing of localization and stabilization of glutamatergic receptors. NLGN1, but not NLGN2 or NLGN3, interacts with PSD95 and NMDA receptors directly (Barrow et al, ; Budreck et al, ), regulates postsynaptic NMDA‐dependent pathways (Chen et al, ; Chubykin et al, ; Hoy et al, ), and affects AMPAR localization (Ko et al, ; Mondin et al, ). It follows that expression levels of NLGN1 specifically would be increased during the functional maturation period of glutamatergic synapses, although compensatory mechanisms do exist (Soler‐Llavina et al, ).…”

Neuroligins Sculpt Cerebellar Purkinje-Cell Circuits by Differential Control of Distinct Classes of Synapses

“…Although it is well established that neuroligins intracellularly bind to PDZ-domain proteins and that different sequences in their cytoplasmic tails may be functionally important (Irie et al, 1997; Iida et al, 2004; Futai et al, 2007; Shipman et al, 2011; Hoy et al, 2013; Chanda et al, 2015), very little functional information about neuroligin cytoplasmic sequences is available. In particular, no structure/function studies on neuroligins have been carried out in a physiological context without affecting endogenous microRNAs.…”

Late onset of Syt2a expression at synapses relevant to social behavior

“…Cropped sections of the 100x or 63x images were saved as separate channels in grayscale bitmap format. Using the Image Pro Plus® (Media Cybernetics) program, puncta labeled by Synapsin 1/2, Gephyrin, and GluR 2/3 were counted manually and co-localization was quantified as performed previously (Hoy et al, 2013). Intensity was measured in cropped sections of 20x images using ImageJ and plotted as neuropil intensity (arbitrary unit, a.u.…”