Gastruloids reveal alternative morphogenetic routes for body-axis elongation with distinct cytoskeletal dependencies.

Substrate availability in mammalian gastruloids determines whether posterior body-axis elongation uses cell-cell forces or substrate-driven traction, with laminin requiring formin activity and focal adhesions.

• Why it matters: Cells can switch morphogenetic programs in different environments, but it is unclear what selects the force-generation strategy during posterior body-axis elongation.
• What they did: Gastruloids were grown free-floating or plated on laminin, then elongation was tested with formin inhibition and focal-adhesion/traction perturbations, alongside transcriptomic profiling.
• The result: On laminin, formin activity and focal adhesion-mediated traction are required, and formin inhibition blocks elongation without detectable transcriptional changes; laminin also biases posterior migratory fates while preserving similar Hox expression.

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