Autism spectrum disorder (ASD) is a highly heritable neurodevelopmental disorder.
SHANK2/3 copy-number variants and truncating mutations account for ~1 % of ASD cases.
POSH (plenty of SH3s, also known as
SH3RF1) is also a high-risk gene for ASD. Previous studies have shown that
Posh gene deletion significantly reduces SHANK2/3 protein levels at postsynaptic density (PSD), impairs dendritic spine maturation, and induces autism-like behaviour with learning and memory deficits in conditional knockout (cKO) mice (Yao et al., 2022). However, the organisational mechanisms of POSH and SHANK2/3 at PSD and the mechanisms regulating synaptic development remain unclear.
In this study, the researchers demonstrated that POSH undergoes liquid-liquid phase separation (LLPS) and co-condenses with SHANK2/3. Functional rescue experiments in
Posh-deficient hippocampal neurons revealed that the co-condensates of POSH and SHANK2/3 are essential for postsynaptic targeting of SHANK2/3 and spine development.
Key findings from the study include:
- POSH undergoes LLPS on its own and recruits SHANK2/3, whose subsequent enrichment further reinforces POSH condensation.
- LLPS of POSH is driven by proline-rich motifs (PRMs) within its intrinsically disordered region and tandem SH3 domains. SHANK2/3 carries cognate PRMs that allow selective integration into POSH condensates, whereas the PRM-deficient partner PSD-95 is excluded.
- Re-introducing wild-type POSH—but not phase-separation mutants—into Posh-deficient neurons fully restored SHANK2/3 synaptic clustering, spine density and morphology.
Because adult-onset re-expression of SHANK proteins can rescue synaptic and behavioral deficits in
Shank-mutant mice, researchers believe that POSH-mediated LLPS not only represents a new mechanism for SHANK2/3 synaptic targeting and synaptic development, but also provides new insights into the pathological mechanisms of ASD and may become a potential therapeutic strategy targeting co- condensation.
This research was supported by the National Natural Science Foundation of China, and the Ministry of Science and Technology of China, etc.
Yao et al. demonstrated that POSH undergoes liquid-liquid phase separation and co-condenses with SHANK2/3, revealing a novel mechanism for organizing SHANK2/3 at synapses and driving spine development.
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