MDGAs interact selectively with neuroligin-2 but not other neuroligins to regulate inhibitory synapse development

Abstract

The MAM domain-containing GPI anchor proteins MDGA1 and MDGA2 are Ig superfamily adhesion molecules composed of six IG domains, a fibronectin III domain, a MAM domain, and a GPI anchor. MDGAs contribute to the radial migration and positioning of a subset of cortical neurons during early neural development. However, MDGAs continue to be expressed in postnatal brain, and their functions during postnatal neural development remain unknown. Here, we demonstrate that MDGAs specifically and with a nanomolar affinity bind to neuroligin-2, a cell-adhesion molecule of inhibitory synapses, but do not bind detectably to neuroligin-1 or neuroligin-3. We observed no cell adhesion between cells expressing neuroligin-2 and MDGA1, suggesting a cis interaction. Importantly, RNAi-mediated knockdown of MDGAs increased the abundance of inhibitory but not excitatory synapses in a neuroligin-2-dependent manner. Conversely, overexpression of MDGA1 decreased the numbers of functional inhibitory synapses. Likewise, coexpression of both MDGA1 and neuroligin-2 reduced the synaptogenic capacity of neuroligin-2 in an artificial synapse-formation assay by abolishing the ability of neuroligin-2 to form an adhesion complex with neurexins. Taken together, our data suggest that MDGAs inhibit the activity of neuroligin-2 in controlling the function of inhibitory synapses and that MDGAs do so by binding to neuroligin-2.inhibitory synapse formation | synaptic cell adhesion | autism | schizophrenia R ecent studies of synapse formation have uncovered a multitude of synaptic adhesion molecules, and human genetic studies have implicated many of these molecules in neuropsychiatric and neurodevelopmental disorders (1-4). However, little is known about the specific pathophysiological mechanisms by which dysfunctions of synaptic adhesion molecules contribute to these complex disorders.Neurexins and neuroligins (NLs) are arguably the most extensively studied synaptic adhesion molecules (1). They are dispensable for initial synapse establishment but act in an isoformdependent manner to specify the maturation of either excitatory or inhibitory synapses (5). There are four NL members in rodents (NL1-NL4) that show distinct synaptic localizations and functions (5). NL2, in particular, has received considerable attention because of its unique localization and function at inhibitory synapses (6). For instance, NL2 controls perisomatic inhibitory synapse maturation together with gephyrin and collybistin, which regulate GABA receptor clustering on neurons (7,8). Moreover, NL2 exhibits differential functions at different types of inhibitory synapses on the same postsynaptic neuron (9). All four NLs likely mediate synapse-promoting activities through direct interactions with presynaptic neurexins, but NLs also perform additional functions in synapse validation that are independent of their binding to neurexins (10).MAM domain-containing GPI anchor proteins (MDGAs), also termed "GPIMs" or "MAMDCs," initially were identified in tumor cells (11). The two homologous MDGA ...

Structural basis for LAR-RPTP/Slitrk complex-mediated synaptic adhesion

“…The psPAX and pMD2G plasmids encode the elements essential for packaging viral particles. HEK293T cell supernatants were harvested 48 h post transfection and purified 46 . Hippocampal neurons infected at DIV3 with control lentiviruses (shControl) or shRNA targeting PTPs (sh-PTPs) or co-infected with lentiviruses expressing PTPs shRNA plus the human shRNA-resistant PTPs splice variant with an MeB insert ( þ PTPs MeB þ ), or PTPs shRNA plus the human shRNAresistant PTPs splice variant without an MeB insert ( þ PTPs MeB À ).…”

Gephyrin: a master regulator of neuronal function?

“…Furthermore, NLGN dimerization seems to be essential for its cell-surface function 66 and for instructing the differentiation of the presynaptic terminal 122 , providing another mechanism for regulating its interactions with synaptic scaffolding molecules. Recently, the MAM domain-containing GPI anchor proteins MDGA1 and MDGA2 (which are Ig superfamily adhesion molecules) were shown to selectively bind to NLGN2 and interfere with its synaptogenic activity 123,124 (FIG. 2D).…”

Gephyrin: a central GABAergic synapse organizer

“…Super-resolution imaging has revealed the existence of distinct subsynaptic domains, where NL-2 and gephyrin are coupled to constitute one domain, whereas IgSF9 is indirectly linked to NL-2 via another domain. 105 It would be informative to use similar approaches to examine systematically the localization of other 'endogenous' inhibitory synapse proteins, such as collybistin, Slitrk3 and MDGA1 106 .…”