Deconstructing body axis morphogenesis in zebrafish embryos using robot-assisted tissue micromanipulation

Microsurgical techniques, such as those used in the early 1900s by Mangold and Spemann, were not only foundational for experimental embryology, but are still in use today. Here, we build on these classic techniques by introducing a user-friendly robotic microsurgery platform that allows precise mechanical manipulation of soft tissues in zebrafish embryos. As a proof of principle, we investigated the contribution of different embryonic tissues to vertebrate anteroposterior (AP) axis elongation and segmentation. Using our platform, we reproducibly targeted precise regions of tail explants, and quantified the response in real-time by following notochord and presomitic mesoderm (PSM) morphogenesis and segmentation clock dynamics. We find an extension force generated through the posterior notochord, independent of notochord cell vacuolation, that is strong enough to buckle the structure. Our data suggest that this force generates a unidirectional notochord extension towards the tailbud because PSM tissue around the posterior notochord does not let it slide anteriorly. These results complement existing biomechanical models of axis elongation, revealing a critical coupling between the posterior notochord, the tailbud, and the PSM, and show that somite patterning is robust against structural perturbations.