Peripheral thickening of the sarcomeres and pointed end elongation of the thin filaments are both promoted by SALS and its formin interaction partners.

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"The authors declare no competing financial interests."

"This project was supported by the Hungarian Science Foundation (OTKA) (K132782 to J.M.) and (FK138894 to S.S.). The project was also supported by The National Laboratory of Biotechnology through the Hungarian National Research, Development and Innovation Office—NKFIH (grant No. 2022-2.1.1-NL-2022-00008 to J.M.), and by the 2022-2.1.1-NL-2022-00012 and TKP2021-NVA-19 projects with the support provided by the Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund, financed under the 2022-2.1.1-NL and the TKP2021-NVA funding schemes (to E.M.).S.S. was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences and by the ÚNKP-22-5 New National Excellence Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund, while M.A.T was supported by the University of Pécs, Medical School (KA-2023-12). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript."