The Shank3 gene encodes a scaffolding protein that anchors multiple elements of the postsynaptic density at the synapse. Previous attempts to delete the Shank3 gene have not resulted in a complete loss of the predominant naturally occurring Shank3 isoforms. We have now characterized a homozygous Shank3 mutation in mice that deletes exon 21, including the Homer binding domain. In the homozygous state, deletion of exon 21 results in loss of the major naturally occurring Shank3 protein bands detected by C-terminal and N-terminal antibodies, allowing us to more definitively examine the role of Shank3 in synaptic function and behavior. This loss of Shank3 leads to an increased localization of mGluR5 to both synaptosome and postsynaptic density-enriched fractions in the hippocampus. These mice exhibit a decrease in NMDA/AMPA excitatory postsynaptic current ratio in area CA1 of the hippocampus, reduced long-term potentiation in area CA1, and deficits in hippocampus-dependent spatial learning and memory. In addition, these mice also exhibit motor-coordination deficits, hypersensitivity to heat, novelty avoidance, altered locomotor response to novelty, and minimal social abnormalities. These data suggest that Shank3 isoforms are required for normal synaptic transmission/plasticity in the hippocampus, as well as hippocampus-dependent spatial learning and memory.

Shank3 is a multi-domain, synaptic scaffolding protein that organizes proteins in the postsynaptic density of excitatory synapses. Clinical studies suggest that ~0.5% of autism spectrum disorder (ASD) cases may involve SHANK3 mutation/deletion. Patients with SHANK3 mutations exhibit deficits in cognition along with delayed/impaired speech/language and repetitive and obsessive/compulsive-like (OCD-like) behaviors. To examine how mutation/deletion of SHANK3 might alter brain function leading to ASD, we have independently created mice with deletion of Shank3 exons 4–9, a region implicated in ASD patients. We find that homozygous deletion of exons 4–9 (Shank3e4–9 KO) results in loss of the two highest molecular weight isoforms of Shank3 and a significant reduction in other isoforms. Behaviorally, both Shank3e4–9 heterozygous (HET) and Shank3e4–9 KO mice display increased repetitive grooming, deficits in novel and spatial object recognition learning and memory, and abnormal ultrasonic vocalizations. Shank3e4–9 KO mice also display abnormal social interaction when paired with one another. Analysis of synaptosome fractions from striata of Shank3e4–9 KO mice reveals decreased Homer1b/c, GluA2, and GluA3 expression. Both Shank3e4–9 HET and KO demonstrated a significant reduction in NMDA/AMPA ratio at excitatory synapses onto striatal medium spiny neurons. Furthermore, Shank3e4–9 KO mice displayed reduced hippocampal LTP despite normal baseline synaptic transmission. Collectively these behavioral, biochemical and physiological changes suggest Shank3 isoforms have region-specific roles in regulation of AMPAR subunit localization and NMDAR function in the Shank3e4–9 mutant mouse model of autism.

Mutations/deletions in the SHANK3 gene are associated with autism spectrum disorders and intellectual disability. Here, we present electrophysiological and behavioral consequences in novel heterozygous and homozygous mice with a transcriptional stop cassette inserted upstream of the PDZ domain-coding exons in Shank3 (Shank3E13). Insertion of a transcriptional stop cassette prior to exon 13 leads to loss of the two higher molecular weight isoforms of Shank3. Behaviorally, both Shank3E13 heterozygous (HET) and homozygous knockout (KO) mice display increased repetitive grooming, deficits in social interaction tasks, and decreased rearing. Shank3E13 KO mice also display deficits in spatial memory in the Morris water maze task. Baseline hippocampal synaptic transmission and short-term plasticity are preserved in Shank3E13 HET and KO mice, while both HET and KO mice exhibit impaired hippocampal long-term plasticity. Additionally, Shank3E13 HET and KO mice display impaired striatal glutamatergic synaptic transmission. These results demonstrate for the first time in this novel Shank3 mutant that both homozygous and heterozygous mutation of Shank3 lead to behavioral abnormalities with face validity for autism along with widespread synaptic dysfunction.

Many animal models of temporal lobe epilepsy (TLE) begin with status epilepticus (SE) followed by a latency period. Increased hippocampal pyramidal neuron excitability may contribute to seizures in TLE. I h , mediated by h channels, regulates intrinsic membrane excitability by modulating synaptic integration and dampening dendritic calcium signaling. In a rat model of TLE, we found bidirectional changes in h channel function in CA1 pyramidal neurons. 1-2 days after SE, before onset of spontaneous seizures, physiological parameters dependent upon h channels were augmented and h channel subunit surface expression was increased. 28-30 days following SE, after onset of spontaneous seizures, h channel function in dendrites was reduced, coupled with diminished h channel subunit surface expression and relocalization of subunits from distal dendrites to soma. These results implicate h channel localization as a molecular mechanism influencing CA1 excitability in TLE.

Analysis of naturally occurring mutations that cause seizures in rodents has advanced understanding of the molecular mechanisms underlying epilepsy. Abnormalities of I h and h channel expression have been found in many animal models of absence epilepsy. We characterized a novel spontaneous mutant mouse, apathetic (ap/ap), and identified the ap mutation as a 4 base pair insertion within the coding region of Hcn2, the gene encoding the h channel subunit 2 (HCN2). We demonstrated that Hcn2 ap mRNA is reduced by 90% compared to wild type, and the predicted truncated HCN2 ap protein is absent from the brain tissue of mice carrying the ap allele. ap/ap mice exhibited ataxia, generalized spike-wave absence seizures, and rare generalized tonic-clonic seizures. ap/+ mice had a normal gait, occasional absence seizures and an increased severity of chemoconvulsant-induced seizures. These findings help elucidate basic mechanisms of absence epilepsy and suggest HCN2 may be a target for therapeutic intervention.

LAY ABSTRACT Mutations in neuroligin genes have been identified in association with autism. This manuscript provides characterization of a specific mutation in the neuroligin-3 gene that has been associated with autism in two brothers. The resulting autism model has alterations in social and cognitive function reminiscent of autism in patients. This model will be useful to understand the role of neuroligin dysfunction as a rare cause of autism. SCIENTIFIC ABSTRACT Multiple candidate genes have been identified for autism spectrum disorders. While some of these genes reach genome-wide significance, others, such as the R451C point mutation in the synaptic cell adhesion molecule neuroligin-3, appear to be rare. Interestingly, two brothers with the same R451C point mutation in neuroligin-3 present clinically on seemingly disparate sides of the autism spectrum. These clinical findings suggest genetic background may play a role in modifying the penetrance of a particular autism-associated mutation. Animal models may contribute additional support for such mutations as functionally relevant and can provide mechanistic insights. Previously, in collaboration with the Südhof laboratory, we reported that mice with an R451C substitution in neuroligin-3 displayed social deficits and enhanced spatial learning. While some of these behavioral abnormalities have since been replicated independently in the Südhof laboratory, observations from the Crawley laboratory failed to replicate these findings in a similar neuroligin-3 mutant mouse model and suggested that genetic background may contribute to variation in observations across laboratories. Therefore we sought to replicate our findings in the neuroligin-3 R451C point mutant knockin mouse model (NL3R451C) in a different genetic background. We backcrossed our NL3R451C mouse line onto a 129S2/SvPasCrl genetic background and repeated a subset of our previous behavioral testing. NL3R451C mice on a 129S2/SvPasCrl displayed social deficits, enhanced spatial learning, and increased locomotor activity. These data extend our previous findings that NL3R451C mice exhibit autism-relevant behavioral abnormalities and further suggest that different genetic backgrounds can modify this behavioral phenotype through epistatic genetic interactions.

Background: BACE1 is a key enzyme in the generation of the Aβ peptide that plays a central role in the pathogenesis of Alzheimer's disease. While BACE1 is an attractive therapeutic target, its normal physiological function remains largely unknown. Examination of BACE1 -/-mice can provide insight into this function and also help anticipate consequences of BACE1 inhibition. Here we report a seizure-susceptibility phenotype that we have identified and characterized in BACE1 -/-mice.

Mutations in phosphatase and tensin homolog deleted on chromosome ten (PTEN) are implicated in neuropsychiatric disorders including autism. Previous studies report that PTEN knockdown in neurons in vivo leads to increased spine density and synaptic activity. To better characterize synaptic changes in neurons lacking PTEN, we examined the effects of shRNA knockdown of PTEN in basolateral amygdala neurons on synaptic spine density and morphology using fluorescent dye confocal imaging. Contrary to previous studies in dentate gyrus, we find that knockdown of PTEN in basolateral amygdala leads to a significant decrease in total spine density in distal dendrites. Curiously, this decreased spine density is associated with increased miniature excitatory post-synaptic current frequency and amplitude, suggesting an increase in number and function of mature spines. These seemingly contradictory findings were reconciled by spine morphology analysis demonstrating increased mushroom spine density and size with correspondingly decreased thin protrusion density at more distal segments. The same analysis of PTEN conditional deletion in dentate gyrus demonstrated that loss of PTEN does not significantly alter total density of dendritic protrusions in the dentate gyrus, but does decrease thin protrusion density and increases density of more mature mushroom spines. These findings suggest that, contrary to previous reports, PTEN knockdown may not induce de novo spinogenesis, but instead may increase synaptic activity by inducing morphological and functional maturation of spines. Furthermore, behavioral analysis of basolateral amygdala PTEN knockdown suggests that these changes limited only to the basolateral amygdala complex may not be sufficient to induce increased anxiety-related behaviors.