During early development, embryos must somehow coordinate the growth of their different tissues to ensure that they reach the correct proportions. Here, Dillan Saunders, Carlos Camacho-Macorra and Benjamin Steventon demonstrate that tissue scaling occurs in post-gastrulation zebrafish embryos. Focusing on the growing zebrafish tail, they find that ablating the spinal cord progenitors that reside in the tailbud results not only in a shortened spinal cord, but also in a shortened paraxial mesoderm, suggesting that these two tissues are adjusting each other’s length to generate a well-proportioned body axis. Spinal cord and paraxial mesoderm progenitors are both derived from a population of neuro-mesodermal competent (NMC) cells, but the authors observe no significant changes to NMC cell division or migration in response to the ablation treatment, and ablation of mesoderm progenitors does not perturb tail length. Using genetic ablation, they remove spinal cord cells across the whole length of the zebrafish body, including in the regions anterior to the tailbud, and show that this recapitulates the effect of spinal cord progenitor ablation. Overall, this work demonstrates that multi-tissue interactions enable proportional body axis formation and suggests that the elongation of the spinal cord is a major driver of pre-somitic mesoderm elongation.
