Dynamics of zebrafish somitogenesis.

Vertebrate somitogenesis is a rhythmically repeated morphogenetic process. The dependence of somitogenesis dynamics on axial position and temperature has not been investigated systematically in any species. Here we use multiple embryo time-lapse imaging to precisely estimate somitogenesis period and somite length under various conditions in the zebrafish embryo. Somites form at a constant period along the trunk, but the period gradually increases in the tail. Somite length varies along the axis in a stereotypical manner, with tail somites decreasing in size. Therefore, our measurements prompt important modifications to the steady-state Clock and Wavefront model: somitogenesis period, somite length, and wavefront velocity all change with axial position. Finally, we show that somitogenesis period changes more than threefold across the standard developmental temperature range, whereas the axial somite length distribution is temperature invariant. This finding indicates that the temperature-induced change in somitogenesis period exactly compensates for altered axial growth.