Gain-of-function p.F28S variant in RAC3 disrupts neuronal differentiation, migration and axonogenesis during cortical development, leading to neurodevelopmental disorder. Issue 3 (20th May 2022)

• Record Type: Journal Article
• Authors: Nishikawa, Masashi; Scala, Marcello; Umair, Muhammad; Ito, Hidenori; Waqas, Ahmed; Striano, Pasquale; Zara, Federico; Costain, Gregory; Capra, Valeria; Nagata, Koh-ichi
• Is Part Of: Journal of medical genetics. Volume 60:Issue 3(2023)
• Page Start: 223
• Page End: 232
• Publication Date: 2022-05-20
• Subjects: central nervous system diseases -- mutation, missense -- gain of function mutation; Medical genetics -- Periodicals; 616.042
• DOI: 10.1136/jmedgenet-2022-108483
• Languages: English
• ISSNs: 1468-6244

Abstract

Abstract : Background: RAC3 encodes a Rho family small GTPase that regulates the behaviour and organisation of actin cytoskeleton and intracellular signal transduction. Variants in RAC3 can cause a phenotypically heterogeneous neurodevelopmental disorder with structural brain anomalies and dysmorphic facies. The pathomechanism of this recently discovered genetic disorder remains unclear. Methods: We investigated an early adolescent female with intellectual disability, drug-responsive epilepsy and white matter abnormalities. Through exome sequencing, we identified the novel de novo variant (NM_005052.3): c.83T>C (p.Phe28Ser) in RAC3 . We then examined the pathophysiological significance of the p.F28S variant in comparison with the recently reported disease-causing p.Q61L variant, which results in a constitutively activated version of RAC3. Results: In vitro analyses revealed that the p.F28S variant was spontaneously activated by substantially increased intrinsic GTP/GDP-exchange activity and bound to downstream effectors tested, such as PAK1 and MLK2. The variant suppressed the differentiation of primary cultured hippocampal neurons and caused cell rounding with lamellipodia. In vivo analyses using in utero electroporation showed that acute expression of the p.F28S variant caused migration defects of excitatory neurons and axon growth delay during corticogenesis. Notably, defective migration was rescued by a dominant negative version of PAK1 but not MLK2. Conclusion: Our results indicate that RAC3 is critical for brain development and the p.F28S variant causes morphological and functional defects in cortical neurons, likely due to the hyperactivation of PAK1.