Autism-Associated Insertion Mutation (InsG) of Shank3 Exon 21 Causes Impaired Synaptic Transmission and Behavioral Deficits

Abstract

SHANK3(also known as PROSAP2) is a postsynaptic scaffolding protein at excitatory synapses in which mutations and deletions have been implicated in patients with idiopathic autism, Phelan-McDermid (aka 22q13 microdeletion) syndrome, and other neuropsychiatric disorders. In this study, we have created a novel mouse model of human autism caused by the insertion of a single guanine nucleotide into exon 21 (Shank3 G ). The resulting frameshift causes a premature STOP codon and loss of major higher molecular weight Shank3 isoforms at the synapse. Shank3G/G mice exhibit deficits in hippocampus-dependent spatial learning, impaired motor coordination, altered response to novelty, and sensory processing deficits. At the cellular level, Shank3 G/G mice also exhibit impaired hippocampal excitatory transmission and plasticity as well as changes in baseline NMDA receptor-mediated synaptic responses. This work identifies clear alterations in synaptic function and behavior in a novel, genetically accurate mouse model of autism mimicking an autism-associated insertion mutation. Furthermore, these findings lay the foundation for future studies aimed to validate and study region-selective and temporally selective genetic reversal studies in the Shank3 G/G mouse that was engineered with such future experiments in mind.

Novel Shank3 mutant exhibits behaviors with face validity for autism and altered striatal and hippocampal function

“…Previously we generated and characterized three other Shank3 mutant mice e4‐9 [Jaramillo et al, ] and G/G [Speed et al, ], ΔC/ΔC [Kouser et al, ]. The ΔC/ΔC Shank3 mice were a collaborative gift from Dr. Paul Worley.…”

“…“L” designates the 100bp ladder. ( C ) RT‐PCR of cDNA from brain tissue of 4‐week old (WT): wildtype, (e4‐9):Shank3 e4‐9 (Jaramillo et al, 2015a), (e13):Shank3 e13 , (G/G):Shank3 G/G (Speed et al, ), ΔC/ΔC: Shank3 ΔC/ΔC (Kouser et al, ) mice. The Shank3 gene contains five functional domains; Ankyrin binding domain from exons 4 to 9, SH3 domain from exons 11 to 12, PDZ domain from exons 14 to 16, Proline rich domain from exon 21, and SAM domain from exon 22.…”

“…Extracellular “field” recordings were performed as previously described [Kouser et al, ; Speed et al, ]…”

Monogenic mouse models of autism spectrum disorders: Common mechanisms and missing links

“…Still, deletion of exons 4–7 (Peça et al, 2011), exons 4–9 (Bozdagi et al, 2010; Wang et al, 2011; Jaramillo et al, 2015), exon 9 (Lee et al, 2015), exon 11 (Schmeisser et al, 2012), exons 13–16 (Peça et al, 2011), or exon 21 (Kouser et al, 2013; Duffney et al, 2015), and an insertion mutation in exon 21 (Speed et al, 2015) all result in ASD-like behaviors to various degrees (reviewed in Bey and Jiang, 2014). Whereas humans with SHANK3 -related ASDs are either haploinsufficient due to a large chromosomal deletion or have point mutations in one copy of their SHANK genes, many of the studies utilizing mouse models only report behavioral abnormalities in homozygous mutants.…”

“…On the other hand, deletion of exon 21 results in decreased LTP, an increased AMPA/NMDA current ratio, decreased mEPSC frequency, and reduced excitatory synaptic strength in the CA1 region of the hippocampus (Kouser et al, 2013) as well as an increased AMPA/NMDA current ratio in layer 5 prefrontal cortex pyramidal neurons (Duffney et al, 2015). The insertion mutation in exon 21 is similar to deletion of exon 21 in terms of hippocampal electrophysiology, but one difference is that LTD, and not LTP, is impaired (Speed et al, 2015). …”