Leukocyte common antigen-related receptor tyrosine phosphatases (LAR-RPTPs) are evolutionarily conserved presynaptic organizers. The synaptic role of vertebrate LAR-RPTPs in vivo, however, remains unclear. In the current study, we analyzed the synaptic role of PTPs using newly generated, single conditional knockout (cKO) mice targeting PTPs. We found that the number of synapses was reduced in PTPs cKO cultured neurons in association with impaired excitatory synaptic transmission, abnormal vesicle localization, and abnormal synaptic ultrastructure. Strikingly, loss of presynaptic PTPs reduced neurotransmitter release prominently at excitatory synapses, concomitant with drastic reductions in excitatory innervations onto postsynaptic target areas in vivo. Furthermore, loss of presynaptic PTPs in hippocampal CA1 pyramidal neurons had no impact on postsynaptic glutamate receptor responses in subicular pyramidal neurons. Postsynaptic PTPs deletion had no effect on excitatory synaptic strength. Taken together, these results demonstrate that PTPs is a bona fide presynaptic adhesion molecule that controls neurotransmitter release and excitatory inputs.

Background Recent progress in genomics has contributed to the identification of a large number of autism spectrum disorder (ASD) risk genes, many of which encode synaptic proteins. Our understanding of ASDs has advanced rapidly, partly owing to the development of numerous animal models. Extensive characterizations using a variety of behavioral batteries that analyze social behaviors have shown that a subset of engineered mice that model mutations in genes encoding Shanks, a family of excitatory postsynaptic scaffolding proteins, exhibit autism-like behaviors. Although these behavioral assays have been useful in identifying deficits in simple social behaviors, alterations in complex social behaviors remain largely untested. Methods Two syndromic ASD mouse models—Shank2 constitutive knockout [KO] mice and Shank3 constitutive KO mice—were examined for alterations in social dominance and social cooperative behaviors using tube tests and automated cooperation tests. Upon naïve and salient behavioral experience, expression levels of c-Fos were analyzed as a proxy for neural activity across diverse brain areas, including the medial prefrontal cortex (mPFC) and a number of subcortical structures. Findings As previously reported, Shank2 KO mice showed deficits in sociability, with intact social recognition memory, whereas Shank3 KO mice displayed no overt phenotypes. Strikingly, the two Shank KO mouse models exhibited diametrically opposed alterations in social dominance and cooperative behaviors. After a specific social behavioral experience, Shank mutant mice exhibited distinct changes in number of c-Fos+ neurons in the number of cortical and subcortical brain regions. Conclusions Our results underscore the heterogeneity of social behavioral alterations in different ASD mouse models and highlight the utility of testing complex social behaviors in validating neurodevelopmental and neuropsychiatric disorder models. In addition, neural activities at distinct brain regions are likely collectively involved in eliciting complex social behaviors, which are differentially altered in ASD mouse models.

Members of the leukocyte common antigen-related receptor protein tyrosine phosphatase (LAR-RPTP) family, comprising PTPσ, PTPδ and LAR, are key hubs for presynaptic assembly and differentiation in vertebrate neurons. However, roles of individual LAR-RPTP members have not been investigated using member-specific conditional knockout mice. Here, we show that loss of PTPδ had no overt effect on synapse development in mouse cultured hippocampal neurons. Moreover, loss of PTPδ in presynaptic CA1 hippocampal neurons did not influence neurotransmitter release in subicular pyramidal neurons, suggesting that PTPδ is not critical for presynaptic function in vivo. Our results demonstrate that PTPδ is not essential for synapse maintenance or transmission, at least in the mouse hippocampus, and underscore the importance of using sophisticated genetic approaches to confirm the roles of synaptic proteins.

IQSEC3, a guanine nucleotide exchange factor for ADP-ribosylation factors (ARF-GEFs) is specifically expressed at GABAergic synapses, and its loss increases seizure susceptibility in mice. However, the contribution of microglia to initiation and/or progression of seizures in IQSEC3-deficient mice has not been investigated. In the current study, we show that mice with hippocampal dentate gyrus (DG)-specific IQSEC3 knockdown (KD) exhibit microglial activation and death of DG granule cell. Furthermore, treatment of IQSEC3-KD mice with minocycline, an inhibitor of microglial activation, blocks DG granule neuron cell death and the occurrence of spontaneous seizures without affecting GABAergic synapse deficits or loss of somatostatin. Our results suggest that microglial activation is involved in a subset of IQSEC3-KDinduced epileptogenesis stages, and that its regulation could be an alternative strategy for managing epilepsy.

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