The physical biology of time and tempo in embryonic pattern formation

A fundamental question in developmental biology is how the tempo of embryogenesis is regulated. Animals with similar body plans can develop at dramatically different speeds, ranging from hours to weeks. Likewise, embryos adjust their developmental pace to environmental conditions, resulting in sped-up development in warm and slowed-down development in cold conditions. However, the mechanisms governing the timing of these patterning processes remain elusive. One of the earliest developmental patterns in vertebrates is the formation of the germ layers, which is driven by diffusible morphogens whose distribution is critical for proper patterning. While we have gained insights into how diffusion and stability of these molecules regulate patterning in zebrafish under laboratory conditions, key questions remain. First, how do internal and external factors influence the time, tempo, and fidelity of pattern formation? Zebrafish and medaka fish differ profoundly in their developmental tempo, but the basis for these differences and their ability to adjust patterning according to temperature is unclear. Second, how do morphogen gradients adjust according to developmental speed? Classical theories predict distinct effects on key biophysical parameters governing gradient formation, but these predictions remain largely untested in vivo. I will present our recent findings addressing these questions using both laboratory strains and wild fish from Lake Konstanz.