Regulator of short-term neuronal synaptic plasticity in the dentate gyrus. Associates with AMPA receptors (ionotropic glutamate receptors) in synaptic spines and promotes AMPA receptor desensitization at excitatory synapses. Component of some AMPA receptors (ionotropic glutamate receptors) complex, at least composed of some AMPA receptor (GRIA1, GRIA2 and/or GRIA3), CACNG2 and SHISA9, as well as low level of DLG4. Brain-specific. Mainly expressed in neurons, including in hippocampus, cerebral cortex, striatum, thalamus, olfactory bulb and cerebellum. Expressed in most brain structures during embryonic and postnatal development. The extracellular domain contains a pattern of cysteine similar to the snail conotoxin Con-ikot-ikot (AC P0CB20), a toxin known to disrupt AMPA receptors (ionotropic glutamate receptor) desensitization. Induces an increase in the paired-pulse ratio of AMPA currents in lateral and medial perforant path-granule cell synapses. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Produced by aberrant splicing sites. Produced by aberrant splicing sites. Belongs to the shisa family. SHISA9 subfamily. Extended N-terminus.