The dystrophin-glycoprotein complex (DGC) is associated with GABAergic postsypaptic densities in hippocampal pyramidal cells, in particular in perisomatic synapses formed by basket cell terminals. Functional and morphological analysis of neuroligin2-knockout (NL2-KO) mice revealed decreased GABAergic transmission and postsynaptic clustering of GABAA receptors and gephyrin, most pronounced in the CA1 pyramidal cell layer (Poulopoulos et al., 2009, Neuron 63:628). We have shown recently in GABAAR alpha2-KO mice a profound impairment of gephyrin, but not alpha1 subunit and NL2 clustering in perisomatic synapses of CA1 pyramidal cells. The preservation of these clusters correlated with the presence of the DGC, suggesting preferential interaction between the DGC, NL2, and alpha1-GABAAR on one hand, and alpha2-GABAAR with gephyrin on the other hand. Here, we investigated by immunofluorescence staining the localization and morphological characteristics of the DGC in pyramidal cells of NL2-KO mice. Compared to wildtype mice, a dispersion of DGC clusters was observed in the pyramidal cell layer, forming numerous small aggregates, only about 40% of them being co-localized with the alpha2 subunit. The phenotype was variable among animals and between cells in the same tissue section. A loss of alpha1 subunit clusters, and to a lesser extent ??2 subunit clusters, was also observed around pyramidal cell somata. The vast majority of spared clusters were not colocalized anymore with gephyrin, unlike in wildtype mice. The lack of NL2 also affected GABAAR clustering in the axon-initial segment at synapses targeted by chandelier cells. In the stratum radiatum, where the majority of GABAergic synapses are devoid of DGC, the impairment of GABAAR and gephyrin clustering was less severe than around cell bodies, reaching about 60% of wildtype values. In contrast, presynaptic GABAergic terminals, stained for VGAT, were not affected in mutant mice. The results indicate that NL2 is required for proper clustering of multiple components of the GABAergic postsynaptic density, including the DGC. Therefore, NL2 and the DGC likely interact to form a protein scaffold contributing to the anchoring of GABAAR and gephyrin at postsynaptic sites.
Impaired clustering of the dystrophin-glycoprotein complex at GABAergic synapses of CA1 pyramidal cells in neuroligin2-deficient mice
PANZANELLI, Patrizia;
2012-01-01
Abstract
The dystrophin-glycoprotein complex (DGC) is associated with GABAergic postsypaptic densities in hippocampal pyramidal cells, in particular in perisomatic synapses formed by basket cell terminals. Functional and morphological analysis of neuroligin2-knockout (NL2-KO) mice revealed decreased GABAergic transmission and postsynaptic clustering of GABAA receptors and gephyrin, most pronounced in the CA1 pyramidal cell layer (Poulopoulos et al., 2009, Neuron 63:628). We have shown recently in GABAAR alpha2-KO mice a profound impairment of gephyrin, but not alpha1 subunit and NL2 clustering in perisomatic synapses of CA1 pyramidal cells. The preservation of these clusters correlated with the presence of the DGC, suggesting preferential interaction between the DGC, NL2, and alpha1-GABAAR on one hand, and alpha2-GABAAR with gephyrin on the other hand. Here, we investigated by immunofluorescence staining the localization and morphological characteristics of the DGC in pyramidal cells of NL2-KO mice. Compared to wildtype mice, a dispersion of DGC clusters was observed in the pyramidal cell layer, forming numerous small aggregates, only about 40% of them being co-localized with the alpha2 subunit. The phenotype was variable among animals and between cells in the same tissue section. A loss of alpha1 subunit clusters, and to a lesser extent ??2 subunit clusters, was also observed around pyramidal cell somata. The vast majority of spared clusters were not colocalized anymore with gephyrin, unlike in wildtype mice. The lack of NL2 also affected GABAAR clustering in the axon-initial segment at synapses targeted by chandelier cells. In the stratum radiatum, where the majority of GABAergic synapses are devoid of DGC, the impairment of GABAAR and gephyrin clustering was less severe than around cell bodies, reaching about 60% of wildtype values. In contrast, presynaptic GABAergic terminals, stained for VGAT, were not affected in mutant mice. The results indicate that NL2 is required for proper clustering of multiple components of the GABAergic postsynaptic density, including the DGC. Therefore, NL2 and the DGC likely interact to form a protein scaffold contributing to the anchoring of GABAAR and gephyrin at postsynaptic sites.
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