Mechanisms driving vertebrate embryonic curvature.

Vertebrate embryos exhibit a characteristic dorsal-to-ventral curl during development. We hypothesize that this process is driven by a differential growth rate, in which the neural tube grows faster than the presomitic mesoderm, creating an inherent bending tendency. To formalize this hypothesis, we developed a "bimetallic strip on a thinning yolk" model. In this model, the magnitude of the differential growth rate determines the embryo's intrinsic curvature, while the underlying yolk acts as a physical constraint which limits curvature. The model predicts a critical yolk area threshold below which the constraint relaxes, allowing the embryo to achieve its inherent, growth-driven curvature. We tested this model via genetic perturbations in zebrafish which specifically alter differential growth rates between the neural tube and presomitic mesoderm. These experiments demonstrate that perturbation of neural tube or paraxial mesoderm growth decrease or increase body curvature, respectively. This analysis provides a quantitative framework for understanding how differential tissue growth and physical constraints shape the vertebrate embryos.