A putative structural transition underlies reliable formation of skeletal muscle.

Myocytes in developing zebrafish myotomes form an ordered chiral twist by position, with a rapid speed reduction once cells span a myotome segment.

• Why it matters: Organ structure becomes reliably defined despite dynamic boundary constraints, but the mechanisms linking early cell behavior to internal muscle organization are unclear.
• What they did: Using live imaging with morphological measures in developing zebrafish, they quantified myocyte twist and movement speed, then applied biophysical perturbations to test mechanical plasticity.
• The result: The findings support a proposed structural transition in the early myotome from fluid-like to solid-like behavior, implying a “frozen” material state that may help drive organ morphogenesis in dense tissues.

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