UC Berkeley

Segmentation is a developmental program in animals that generates semi-repetitive structures along the body axis. In vertebrates, somites are formed sequentially from the mesoderm of the extending tailbud, eventually giving rise to structures such as axial muscles and vertebrae. Somites form with great regularity, every thirty minutes in zebrafish. The periodicity of somite formation is controlled by a set of oscillating genes known as the segmentation clock. To better understand the dynamics of the clock and its role in patterning somites, I have explored its behavior through an in vivo clock reporter, her1:her1-venus. I show that individual cells in the presomitic mesoderm express oscillating clock expression, consistent with predictions made by mathematical modeling and analysis in fixed embryos. I am able to rapidly track a large number of PSM cells using novel semi-automated cell tracking and fluorescence quantification programs. Through these methods, I find that the clock oscillations are coordinated through the Notch pathway, and a loss of Notch function causes slower and desynchonized clock oscillations. I also explore the interaction of mitosis and the segmentation clock, and find the two processes are connected. Finally, I investigate the slowing of the segmentation clock in real-time, and find that oscillations in the anterior PSM are about twice the periodicity of somitogenesis. This has interesting implications for the role of the segmentation clock in patterning somites, including the potential to polarize somites. By studying the segmentation clock in real-time, I am able to better investigate and understand the mechanisms driving somitogenesis.