PhD Scientific Days 2026

Poster Session 3.J - Theoretical and Translational Medicine

Non-muscle Actinopathy-associated Loss-of-function Variants of Actin Modulate the Reorganization Properties of the Actin Cytoskeleton

Name of the presenter

Dakos, Kira

Institute/workplace of the presenter

Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary

Authors

Kira Dakos¹, Éva Gráczer¹, Tamás Bozó¹, Katalin Pászty¹, Nataliya Di Donato², Miklós Kellermayer¹, Andrea Varga¹
1: Department of Biophysics and Radiation Biology, Semmelweis University, Budapest, Hungary
2: Department of Human Genetics, Hannover Medical School, Hannover, Germany

Text of the abstract

Introduction: Variants in the ACTB gene encoding for cytoplasmic β-actin result in a group of rare disorders called non-muscle actinopathies. The subgroup of affected patients with ACTB pLoF (predicted loss-of-function) mutations shows clinical symptoms, including intellectual disabilities, mild microcephaly and thrombocytopenia.
Aims: To uncover the cellular and molecular effects of a missense variant, G302A, and a four-amino-acid deletion, S338-I341del, in patient-derived fibroblast cells.
Methods: We used various microscopic techniques (confocal, super-resolution and atomic force) to visualize and assess the cellular properties of the actin cytoskeleton that could potentially change due to the mutations. We also challenged the cells with monolayer stretching and followed the mechanically-induced reorganization of the actin cytoskeleton via confocal microscopy and western blot.
Result: We found that neither of the mutations affected the organization of actin or the width of the actin-filament bundles, while the mutation G302A reduced the stiffness of the cells. The latter effect might be associated with the misorganization of tubulin in the mutant cells. Our monolayer stretching experiments revealed that the mutant cells behaved differently from wild-type cells. G302A mutant cells showed more dense actin filament bundles within the cells. At the same time, the extent of cofilin reorganization from the cell periphery was increased upon stretch, and this correlated with an increased cofilin phosphorylation. In the case of the deletion, the phosphorylation of myosin light chain, important in counteracting external force, was drastically reduced. We could partially rescue this fascinating effect by overexpressing the active form of the formin mDia. This may help devise an accessible treatment for patients.
Conclusion: Taken together, we found that two variants associated with ACTB pLoF disorder affect the reorganization of actin, which might be important for neuronal migration, necessary for creating a properly connected neural network.