Abstract

Vertebrates are characterized by a left-right symmetric muscle and skeletal system that emerges from bilateral somites during embryonic development. Left-right symmetry is vital for adult mechanical movements and a loss of symmetry is associated with debilitating skeletal disorders such as scoliosis. Symmetry is often assumed to be a default state in somite formation, however, it remains unknown how robust somite shapes and sizes at the same position along the body axis emerge on the left and right sides of the embryo.

By imaging left-right somite formation in zebrafish embryos using light-sheet microscopy and by developing automated image analysis tools, we reveal that initial somite anteroposterior lengths and positions are imprecise and consequently many somite pairs form left-right asymmetrically in contrast to the textbook view. Strikingly, these imprecisions are not left unchecked and we find that lengths adjust within an hour after somite formation, thereby increasing morphological symmetry. We discover an error correction mechanism, where length adjustment is facilitated by somite surface tension, which we show by comparing in vivo experiments and in vitro single-somite explant cultures with a mechanical model. We propose that tissue surface tension provides a general mechanism to adjust shapes and ensure precision and symmetry of tissues in developing embryos.