Formation control between leader and migratory follower tissues allows coordinated growth.

Coordinated growth of multiple tissues is fundamental to shaping our body, but the underlying mechanisms remain underexplored. In zebrafish embryos, midline tissues composed of the notochord, floorplate, and hypochord elongate synchronously with their lengths aligned. We show that floorplate and hypochord cells collectively migrate posteriorly along the nascent notochord extracellular matrix as it extends posteriorly, maintaining the tripartite configuration. Fibroblast growth factor-mediated migration in a spatially graded manner causes cell stretching, which triggers Yap-dependent proliferation and controls floorplate and hypochord growth. Supported by mathematical modeling, we further suggest that their growth is fine-tuned by mechanical tethering to the notochord via cadherin 2 at the posterior end. We propose that the notochord instructs and sustains the tripartite formation via leader-follower formation control, a strategy from engineering that spatially organizes multiple agents to coordinate the growth of the midline tissues.