Molecular Dissection of Neurodevelopmental Disorder-Causing Mutations in CYFIP2
Matthias Schaks1,2, Michael Reinke3, Walter Witke3
1Division of Molecular Cell Biology, Zoological Institute, Technische Universität Braunschweig, 38106 Braunschweig, Germany.
Abstract:
Actin remodeling is frequently regulated by antagonistic activities driving protrusion and contraction downstream of Rac and Rho small GTPases, respectively. WAVE regulatory complex (WRC), which primarily operates downstream of Rac, plays pivotal roles in neuronal morphogenesis. Recently, two independent studies described de novo mutations in the CYFIP2 subunit of WRC, which caused intellectual disability (ID) in humans. Although mutations had been proposed to effect WRC activation, no experimental evidence for this was provided. Here, we made use of CRISPR/Cas9-engineered B16-F1 cell lines that were reconstituted with ID-causing CYFIP variants in different experimental contexts. Almost all CYFIP2-derived mutations (7 out of 8) promoted WRC activation, but to variable extent and with at least two independent mechanisms. The majority of mutations occurs in a conserved WAVE-binding region, required for WRC transinhibition. One mutation is positioned closely adjacent to the Rac-binding A site and appears to ease Rac-mediated WRC activation. As opposed to these gain-of-function mutations, a truncating mutant represented a loss-of-function variant and failed to interact with WRC components. Collectively, our data show that explored CYFIP2 mutations frequently, but not always, coincide with WRC activation and suggest that normal brain development requires a delicate and precisely tuned balance of neuronal WRC activity.
Insights
Mutations in CYFIP2, linked to intellectual disability, often enhance WAVE regulatory complex (WRC) activity through various mechanisms. Precise WRC balance is crucial for normal brain development.
Area of Science:
- Cell Biology
- Neuroscience
- Genetics
Background:
- Actin remodeling is vital for neuronal morphogenesis, regulated by small GTPases like Rac and Rho.
- The WAVE regulatory complex (WRC), downstream of Rac, is critical for these processes.
- De novo mutations in CYFIP2, a WRC subunit, have been linked to intellectual disability (ID).
Purpose of the Study:
- To experimentally investigate the functional impact of ID-associated CYFIP2 mutations on WRC activity.
- To elucidate the mechanisms by which CYFIP2 mutations affect WRC function.
- To understand the relationship between WRC activity balance and normal brain development.
Main Methods:
- Utilized CRISPR/Cas9 technology to engineer B16-F1 cell lines expressing ID-causing CYFIP2 variants.
- Assessed WRC activation levels in cells reconstituted with different CYFIP2 mutants.
- Analyzed mutation positions relative to Rac-binding sites and the WAVE-binding region.
Main Results:
- Seven out of eight tested CYFIP2 mutations promoted WRC activation, indicating frequent gain-of-function effects.
- Identified at least two distinct mechanisms driving WRC activation by these mutations.
- One mutation near the Rac-binding site facilitated Rac-mediated activation, while others affected the WAVE-binding region.
- A truncating CYFIP2 mutant exhibited loss-of-function, failing to interact with WRC components.
Conclusions:
- ID-associated CYFIP2 mutations frequently lead to WRC hyperactivation, though not universally.
- The precise balance of neuronal WRC activity is essential for proper brain development.
- Understanding these molecular mechanisms provides insight into the pathophysiology of intellectual disability.
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