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Abstract

Postsynaptic scaffolding proteins like SHANK1-3 stabilize the formation, organization and signal transmission at the glutamatergic synapses through numerous protein interactions. All three SHANK genes are expressed in multiple isoforms that cooperate to form a complex and a developmentaldependent scaffold organization at glutamatergic synapses. Those modulatory proteins are involved in the spatial organization of postsynaptic receptors, the efficiency of synaptic transmission and the plasticity of synapses. As a consequence, the synaptic transmission is responsive to structural changes within the SHANK scaffold, as evidenced by (I) the high number of ASD patients with mutations and copy number variations in the SHANK genes, (II) the diverse clinical phenotypes ranging from ASD to mania-like phenotypes in numerous Shank knock-out mouse models and (III) the 4-fold higher prevalence of ASD in males, which might be explained in some cases by the sex dimorphic expression of SHANK. Indeed, the here presented investigation of Shank expression in mice revealed significantly higher SHANK levels both in late stage male embryos and earlypostnatal male pups during their peak of testosterone level. Moreover, the treatment of human neuroblastoma cells with dihydrotestosterone and 17β-estradiol increased the expression of all three SHANK genes, demonstrating a direct sensitivity of SHANK genes to the sex hormones. For the functional analysis of specific SHANK isoforms in mice, the endogenous regulation of the Shank scaffold was blunted in favor of a strong constitutive, doxycycline-regulated overexpression of transgenic SHANKs. The spatiotemporal-controlled overexpression of either SHANK2A or the truncated SHANK2A(R462X) in the mouse glutamatergic forebrain neurons was correlated with specific ASD-like phenotypes including hyperactivity, repetitive behavior and impairments in social and novelty behaviors. When the transgenes were switched off in adulthood, specifically the impaired sociability was unexpectedly rescued in mice of both mouse lines. The effect of SHANK2A but not SHANK2A(R462X) overexpression inhibited the developmental-dependent AMPAR subtype switch in the basal dendrites of the hippocampus. In addition, the synaptic protein components were altered differently in both mouse lines, indicating mainly presynaptic components in SHANK2A(R462X) and more postsynaptic components in SHANK2A overexpressing mice. These results identified the differential regulation of endogenous SHANK as critical modulators of neuronal networks that are critically involved in learning and social behaviors.