Clocks and timers in developing embryos

Andy Oates

Some biological oscillators function throughout the life of an organism, for example the circadian clock, whereas others have a more restricted duration, particularly in embryogenesis. The “segmentation clock” is a multi-cellular patterning system of genetic oscillators thought to control the rhythmic and sequential formation of the vertebrate embryo's body segments. Individual oscillating cells are synchronized with their neighbors, forming a coherent wave pattern of gene expression. How these wave patterns arise and how they are regulated during embryogenesis is not clear. I will describe recent progress in understanding the behavior of individual cells from the zebrafish as they slow their oscillations and differentiate during segmentation, and discuss how this gives rise to the tissue-level wave patterns. Central to this understanding is the concept of a timer that regulates the duration of a clock.